Between the Poles

Initiative to develop open standards for AEC and geospatial interoperability

The effects of population growth, urbanization and climate change are motivating us to contemplate serious changes in how we build and maintain buildings and infrastructure. This change will require new tools. There are important industry drivers that suggest that AEC (architecture, engineering and construction) and geospatial interoperability is one of them. A specific challenge currently facing the AEC and geospatial industries is integrating building information models (BIM) and geospatial infrastructure models for full life-cycle project workflows. Autodesk and ESRI have announced a partnership to further the integration of AEC and geospatial models and data which is already showing tangible results, but in a proprietary environment. A recent paper by the Integrated Digital Built Environment (IDBE) joint working group working group, a collaborative effort by buildingSMART International (bSI) and the Open Geospatial Consortium (OGC) to further open standards for AEC/geospatial interoperability, has identified the conceptual and other incompatibilities between the geospatial and AEC modeling of built infrastructure and suggested a way forward toward addressing incompatibilities.

Clashing tectonic plates

The BIM+geospatial problem is the latest symptom of a broader problem. I began working in the utility and telecom sector in 1993, specifically in developing software for records management (called network documentation outside of North America), and at that time the magnitude of the AEC+geospatial cultural mismatch problem was just beginning to be appreciated by utilities and telecoms. The Between The Poles blog is nearly 15 years old and one of the persistent themes from the very beginning in 2006 was the challenge of integrating CAD and GIS data in a common workflow (some examples; 2006, 2007, 2008 ). In utilities and telecoms planners tend to use GIS tools, engineers and designers CAD tools, construction folks in the field paper CAD drawings, and asset managers GIS integrated with their FM tools. Fashioning AEC and geospatial data into an efficient data flow from planning through design and construction to operations and maintenance continues to be a challenge.

There are parallels between what happened in the 1990s in unsuccessfully addressing CAD+GIS interoperability and the current challenge of BIM+geospatial interoperability. But there are also important differences which provide grounds for optimism that the availability of open standards for both BIM and geospatial, a vibrant open source geospatial community, and a new willingness on the part of major software players in the BIM and geospatial industries will make it possible to successfully address the latest interoperability challenge facing the AEC (architecture, engineering and construction) and geospatial industries.

Building information modeling (BIM) has been applied to design-build construction projects for many years. A growing number of countries are mandating BIM for public projects. While the UK government has said that "...we know that the largest prize for BIM lies in the operational stages of the project life-cycle", until recently there has not been hard data to support this conjecture. Similarly there has been only anecdotal support for an integrated BIM and geospatial approach for design, build, operate and maintain projects. Now we are beginning to see data from real world projects that offer evidence for the benefits of an integrated BIM+geospatial full lifecycle approach for construction projects.

Research in the Netherlands at the Delft University of Technology delved into interoperable digital building and infrastructure model standards developed to serve the AEC (architecture, engineering and construction) and geospatial sectors. Specifically, the research was focused on translating the geometry and topology of 3D digital BIM models represented in buildingSMART's Industry Foundation Classes (IFC) standard into 3D forms compatible with the Open Geospatial Consortium's CityGML standard. The researchers found is that there is more than one way to transform a BIM model to CityGML. While it was possible to transform most BIM models, it is not possible to convert all BIM models to CityGML.  The findings of this research has reemphasized the challenge of integrating AEC and geospatial data, the first major industrial symptom of which appeared over 25 years ago in the form of 2D integration of CAD and GIS.

Comparison of IFC, CityGML, and LandInfra

The IDBE working group is a joint collaboration between buildingSMART and the OGC.  Among the first products of IDBE is a paper Built environment data standards and their integration: an analysis of IFC, CityGML and LandInfra that described the incompatibilities and similarities among three open standards used in the AEC and geospatial worlds.

The three standards are IFC (Industry Foundation Classes), developed by bSI, is used predominantly for exchange of rich, fine-scale building and infrastructure data in the AEC industry, CityGML, an OGC standard, for capturing large scale urban data including buildings and transportation infrastructure originally for simulations, and LandInfra, jointly developed by bSI and OGC, for modelling land and civil engineering infrastructure facilities and designed as a successor to LandXML.

An important difference among the standards is how real-world objects are conceptualized.  IFC represents a building as an aggregation of building elements such as walls, doors, and windows, CityGML represents internal building volumes as rooms, and LandInfra represents buildings as features of a facility with only an outer shape and footprint.

Another important difference is coordinate systems. IFC uses a rectilinear coordinate system to represent structures in engineering precision over relatively small, flat surfaces.  CityGML and LandInfra model structures that need to take into account the Earth's curvature and therefore use an appropriate geographic projection system.

The standards use different geometric representations of objects.  CAD and BIM design tools use splines, nurbs, spirals and many other parametrized forms.  Geospatial applications generally use points and multi-point lines and polygons.

Topological relationships are also handled differently. In CityGML, topologies such as containment or spatial adjacency are represented implicitly in the boundaries between different geometric objects.  IFC defines objects and their geometries and separately and explicitly identifies topological relationships between them.

Level of Detail and Level of Development (LOD) are handled differently.  CityGML uses LOD to progressively define more detailed representations of a structure. For example, for a house; LOD 0 is a building footprint; LOD1, a 3D volume; LOD 2 includes a 3D roof geometry, LOD 3, windows and doors, and LOD 4 detailed structures and furniture. Levels of Development in BIM refer to levels of progress through a construction project and does not correspond to LODs in CityGML. There is no concept of LOD in LandInfra.

Conclusion

The consequence of these differences among the standards is that software interoperability and data integration are difficult.  Three approaches to resolving this interoperability challenge have been proposed.

• Schema mapping: This approach attempts to map each object in one standard to be mapped onto its nearest match in another standard.  The TU Delft research described earlier investigated this approach and concluded that unambiguous mappings between CityGM and IFC was not possible in all cases.
  
• Federation: Another approach is to support multiple schemas in one representation.  For example, a Revit BIM model can be displayed in a geospatial environment.This limits the generality of some operations such as spatial search, spatial analytics, and CAD and BIM operations.
  
• Link referencing: A third approach is a linked federation using embedding links in the primary model to components from instances of secondary schemas. The feasibility of such an approach was confirmed in OGC Testbed 4 (2007), in which web services were used for 'merging' CAD, GIS and BIM data.

Next steps

The IDBE has made several recommendations for moving forward to resolve the latest AEC/geospatial interoperability challenge in an open, standards-based way.

• Identify and prioritize uses cases.
• Compile a shared vocabulary and a shared resource for identifying synonyms across different domains.  An example of the latter is the CB-NL developed in the Netherland for mapping synonyms across the construction life-cycle.
• Develop a best practice document for coordinate systems for 3D georeferencing.
• Devise a system of common unique identifiers (Oids) for real-world, physical objects that remain
  constant and unique.
• Collaborative approach for harmonizing conceptual models.
  

I would add that owners of buildings and infrastructure, recognizing that an important benefit of open interoperability standards is increased competition among software vendors, should consider ways that open standards are incorporated into their procurement requirements.  Government procurement was a major driver that motivated virtually all BIM tool vendors to incorporate IFC support into their products.

Augmented reality enables simplified design workflows

Engineering design is typically done on a desktop computer, using CAD or BIM software. Models are viewed in 3D or 2D on a monitor. Increasingly they can be viewed in mixed reality.  At a SPAR3D conference three companies in the construction sector, Gensler (a collaborative design firm), McCarthy (a commercial construction firm), and Martin Brothers Construction (a heavy civil construction firm), demonstrated how they were using mixed reality on real-world projects.  For example, Martin Brothers demonstrated building a bathroom pod with Hololens. The bathroom pod was designed using a standard design application such as Revit or Sketchup, then projected onto the reality of a shop floor were it was constructed using the full-scale virtual reality projection of the design into the shop. The next step is bidirectional between the mixed reality environment and the authoring design tool. This makes it possible for changes made in the mixed reality environment to be visible in Revit or Sketchup where they can be incorporated into the design. It is also possible to reverse this process where design changes made in Revit or Sketchup are simultaneously visible in the mixed reality environment.

Stéphane Côté of Bentley has taken this one step further and suggested that the design and visualization process should really be a continuum involving design, markup, and visualization.  To enable this to happen Stéphane's team developed a simple set of drawing tools along with features that enhance drafting accuracy, such as angle, length and element snapping.  But most innovative was the ability to snap to real world objects in augmented reality.  This is illustrated in a video by designing an extension to a table.  To do this the designer simply snaps to the table in augmented reality and then designs the extension seeing exactly what it looks like including accurate measurements such as lengths and angles.

As a real world example, when an engineer needs to design a bypass system between two existing pipes, normally he/she would have to take measurements of the pipes or scan them using a laser scanner. These measurements would then be imported into a CAD application where they would be used as the basis for the design.  It might even be necessary to iterate this process once or twice to ensure the accuracy of the design.  With an augmented reality design tool such as that created by Stéphane's team the design could be done on-site, avoiding the initial measurement step and being able to see immediately if the design fits accurately between the existing pipes.

Cost of underground utility damage represents a major drag on national economies

Underground utility damage is expensive. Several jurisdictions have attempted to estimate the cost of underground utility damage for individual incidents and for entire national economies. Costs can be broken down into direct costs and indirect costs. Direct costs include the costs of sending a crew to repair the damaged pipe or cable. Indirect costs include many factors that are often hard to quantify such as traffic disruption, injuries and fatalities among workers and the public, and the lost custom that local businesses experience. An important conclusion from the research into the cost of underground utility damage is that it represents a major drag on national economies, $50 to $100 billion annually in the U.S., £ billions in the U.K., and € 1 billion in the Netherlands.

UK

About 4 million excavations are carried out on the UK road network each year to install or repair buried utility pipes and cables.  Research at the University of Birmingham on 3348 incidents of damage to underground utilities determined the direct costs of utility damage during construction.

 

Facility	Avg cost per strike in 2016
Electricity	£ 970
Gas	£485
Telecom	£400
Fibre-optic	£2800
Water	£300-980

 

The researchers found that the true costs associated with utility strikes is much higher than this. Direct costs include the costs of sending a crew to assess and repair the damaged pipe or cable. Indirect costs include the impact of traffic disruption as a result of the strike, any injuries and other impacts on the health of the workers directly involved and the public in the immediate neighbourhood, and the lost custom that businesses experienced as a result of the traffic disruption. The research revealed that the true cost is about 29 times the direct cost. This is a startling result which indicates that the cost to society of underground utility strikes is much, much larger than is generally believed.

US

The CGA compiles information on the direct cost of damage to underground infrastructure for different types of underground infrastructure.

 

Facility	Avg cost per damage 2016
Natural gas	$5,914.00
Telecom	$3,022.00
Electric	$4,905.00
Cable TV	$2,190.00
Water	$3,003.00
Sewer	$5,163.00
Liquid pipeline	$7,711.00
Steam	$1,800.00
Average	$4,021.00

 

At an average cost of $4000 per hit, the CGA estimates that the direct cost to the U.S. Economy is about $1.5 billion (or roughly double this if the number of incidents annually is actually closer to 800,000). The CGA emphasizes that this is a conservative minimum estimate and does not include indirect and social costs.

Scott Landes, of Infrastructure Resources LLC, has compiled a comprehensive list of the direct, indirect and societal cost of damage to underground infrastructure.

 

Items that may or may not be collected

• External collection costs/agency commissions

• Barricades/traffic control

• Permits (city/county/state/provincial) to install replacement cables/pipelines

• Legal fees and litigation costs

• Exposing the damage for repair

• Materials used in repair

• Restoration of the area

• Actual cost of internal labour

• Heavy equipment used

• Generator/power equipment

• Food, lodging, and travel expense

• Emergency mobilization (contractor/locator)

Time

• Damage investigation, on-site and follow-up

• Internal staff collection efforts

• Out of service complaints

• Insurance resolution discussions

• Overtime for unexpected increases in workload

• Employee time/travel for depositions/trial

Overlooked/difficult to track

• Lost customers

• Customer loss of use (refunds/credits)

• Resolution of customer complaints

• Engineering/reengineering due to damage

• Establishing outage bridge to coordinate services interruption

• Support staff (3-20) for outage bridge

• Workload delays

• Future failure points (damage may weaken system and lead to future failure unattributed to 3rd party)

• Damage data capture and submission (software and/or manual)

• Emergency on call ticket notifications

• Facility owner records updates

• Reporting requirements (FAA, 911, PHMSA)

Soft costs

• Loss of brand confidence

• Negative public feedback

• Difficulty maintaining customer relationships, especially large businesses, with inconsistent services

Societal costs

• Loss of 911/emergency services

• Business closing

• Employee downtime

• Road closures/traffic delays

This is a very interesting list because it provides a perspective on the comprehensive impact on society of disruptions to utilities and telecom resulting from underground damage during construction.

If the ratio of total to direct cost determined by the researchers at the University of Birmingham is applicable to the US, it would mean that the total estimated impact of unknown or poorly located underground infrastructure on the U.S. economy is between $50 billion and $100 billion annually.

Netherlands

Network operators are required to report all incidents of damage to their infrastructure including location, cause and other information. Based on this and other information Kadaster publishes an annual report with statistics on underground utility damage. This information can be used to estimate direct costs of damage to underground infrastructure.

 

Damage to underground utilities in 2018
Annual excavation damage	41,169
Direct costs from damage	€ 34,500,000
Average repair cost per excavation damage	€ 838

 

If the estimated direct cost is multiplied by 29X from UK research to estimate the total cost, underground utility damage costs the Dutch economy about € 1 billion annually.

 

An important conclusion from the research into the cost of underground utility damage is that it represents a major drag on national economies, $50 to $100 billion annually in the U.S., £ billions in the U.K., and € 1 billion in the Netherlands.

 

Acoustic location works where EM and GPR techniques don't for locating underground infrastructure

There have been significant advances in technologies for detecting underground infrastructure including inertial locating, novel radar technologies applied to ground penetrating radar (GPR), and software for post processing GPR signals to produce tomographic images. Each has its limitations. Inertial locating is restricted to known pipelines.  Electromagnetic detection (EM) is restricted to conducting cables and pipes and low conductivity soil conditions. GPR can't distinguish between different types of utilities and its effectiveness is also limited under high conductivity soil conditions. Recently there is evidence that acoustic surveying may provide a technology that complements existing techniques; unlike EM and GPR methods it can detect non-metallic objects and is not affected by type of surface, soil type or moisture content.

Cartacoustics, LLC, has developed an acoustic surveying technique that uses specially crafted audible sound wave packets to locate and trace buried utilities. Sound waves are crafted into recognizable patterns and sent into the ground using special speakers. Ultra sensitive geophones then listen for reflected sound waves with the crafted patterns. Post-processing determines the time of the flight of the waves to estimate the depth of the objects that reflected the sound waves. Because of the frequencies used, the ability to detect underground objects is not affected by the type of surface (asphalt, concrete, dirt, or sod), the type of soil such as clay and the moisture content of the soils, all of which reduce the effectiveness of GPR. Acoustic locating has been successfully used in saturated soils, rocky and sandy soils, and in high-clay content soils.  It has also been applied successfully with four inches of snow on the ground and immediately after a hard rain.  In many soils GPR may be only able to detect objects a few meters down.  Acoustic location is effective 30 feet or 10 meters down. The survey is non-invasive and non-destructive.

Acoustic surveying involves sampling at a number of points in the field area and then interpolating between the survey points to detect man-made structures such as cables or pipelines and their approximate locations. In addition to manufacturing the acoustic field collection hardware, Cartacoustics has also created several deliverable map products to present placement of the detected underground structures. ASTmap!™ contains a series of products that summarize the data collected in an acoustic underground survey at various levels of fidelity. A 2D map product called a DIGsafe! map highlights areas where underground structures have been located and areas that are free from acoustic returns. These areas show where it is safe to dig and where caution is required. Two additional ASTmap! products provide more detailed information on depth of cover to detected structures and can be provided in various CAD formats.  For a typical day-long collection, the processing and analysis takes a day or two. This means that results are generally available within a week of the survey for review.

To validate the technology Cartacoustics has surveyed a number of sites across the country.  In the first such surveys they chose sites with manholes, fire hydrants, water valves and gas metering stations that are obvious indicators of subsurface structures.  Acoustic surveys were conducted along the streets and right-of-ways containing these features. The acoustic returns revealed the features in the correct locations and depths as expected from nearby manholes. 

Brown and Caldwell (BC) recently employed Cartacoustics’ technology to survey a half-acre portion of Metro Vancouver’s Annacis island Wastewater Treatment Plant (AIWWTP) in Vancouver, British Columbia. In the past, mapping underground infrastructure would have employed traditional techniques such as EMI, GPR and excavation. At this site, the soil conditions render GPR and EMI techniques ineffective, and excavation would have been required.

To acquire the needed subsurface data, an acoustic survey was conducted on a rectangular grid with 3-meter spacing between points. At each point the time of flight and horizontal location was recorded. Collected data are post-processed and detected objects were correlated from the recorded information of all surveyed points to reveal objects extending across multiple adjacent survey points and objects that were uncorrelated across adjacent points. The result of the post-processing is a 3D model of underground objects. Comparing the 3D model against the plant’s engineering drawings and Building Information Model (BIM) showed very strong correlation between expected infrastructure and the acoustic results. While the correlation was strong, the results also offered a couple of surprises – one pipe that did not follow the expected track according to the engineering drawings and several areas of uncorrelated data. This latter is suspected to represent “debris fields”; the area surveyed is in the oldest part of the plant and the “debris fields” are likely construction waste that was buried during early construction of the facility.

Many in the subsurface utilities location industry rely on a multi-sensor approach including electromagnetic detection, ground penetrating radar and other technologies.  The acoustic survey results acquired to date suggest that this acoustic-based technology has the potential to add an important complementary technique to the typical underground locating quiver of EM and GPR.

Hybrid GIS and survey system tackles low quality underground utility location information

At the fourth Digital Underground Connect (DUConnect) session, Rob Martindale, Utility Program Manager at the Colorado Department of Transportation (CDOT) provided an overview of a remarkable initiative by the State of Colorado to address the challenge of improving the quality of information about the location of underground utilities, specifically as-builts.

According to the Federal Highway Administration (FHWA) underground utilities are a major cause of highway construction schedule and budget overruns. In addition to construction delays, damage to underground utilities during construction makes every construction project a potential disaster site with risks to workers and the public.  All states and most provinces in North America have legislation creating one call centres that connect network operators to excavators for locate services.  However, statistics collected by the Common Ground Alliance have not shown a reduction in underground utility damage in recent years.  In 2017 as the result of a gas explosion Colorado began a comprehensive approach involving legislation, technology and regulation to address the challenge of incomplete, inaccurate and out-of-date information about underground utilities. 

In 2017 there was an explosion at a home in Firestone, Colorado that resulted in two deaths and a serious injury. Prevously in 2014 the Pipeline and Hazardous Materials Safety Administration (PHMSA) had found that the Colorado one-call system had serious deficiencies. Most importantly it found that the current legislation did not assign an agency to enforce the legislation. In 2018 the Colorado legislature revised its one-call legislation. The latest legislation differs from the one call legislation in other states and provinces for two important reasons

1. It explicitly mandates subsurface utility engineering (SUE) during engineering design for public civil engineering projects to determine the 2D location of underground utilities to ASCE 38 quality level B by a licensed professional engineer. (ASCE quality level B requires the application of remote sensing detection technologies such as electromagnetic detection and ground penetrating radar.)
2. It has provisions to ensure that owner/operators provide complete, accurate and current "as-constructed" electronic drawings recording the location of their underground facilities with penalties if they are not compliant.
   

Inspection by CDOT did not support utility supplied as-built

At the DUConnect session Rob outlined how the new legislation is being implemented and how it works in practice. For decades one of the challenges facing utilities has been how to integrate survey data, engineering design (as-designed), typically CAD files, and what is actually constructed (as-constructed), which may or may not be recorded as red lines on paper construction documents, into utility GISs.  The result has been that the data in utility GISs is incomplete, inaccurate, and out-of-date.  For the past few decades there has been little motivation for network operators to improve the quality of their information about the location of underground facilities.  The new legislation provides for on-site construction oversight to ensure that complete and accurate "as-constructed" documents in electronic form are submitted at the completion of construction.

For collecting and maintaining location information about underground utilities CDOT has adopted a hybrid approach that incorporates elements of survey and GIS technology and practices.  This approach enables data from disparate sources including surveys, GIS, design files, construction documents, subsurface utility engineering reports, and utility relocations into a shared database managed by a server application (Transparent Earth) that is accessible in the field from a handheld app (Pointman). An advantage of this approach is that it is not only a GIS but enables the capture of survey grade location information. 

Data collection during utility relocation projects

For new and relocated underground utilities it enables all location information to be captured at survey level including the metadata typically recorded in a surveyor's field book such as when the survey was conducted, who conducted it, the equipment used, and so on.

In the CDOT system all location information has pedigree or metadata associated with it. The system was developed by a private developer Prostar Geocorp.  The system is natively built to be open source using GeoServer and seamlessly integrates with other modern technologies such as Bentley and ESRI and legacy systems of record such as GE Smallworld.  It uses standard map services such as Google Maps, Bing, and OpenStreetMap for base mapping as well as LiDAR and drone imagery when higher levels of precision are required. The ProStar system leverages Open Geospatial Consortium (OGC) standards including Web Mapping Services (WMS) and Web Feature Services (WFS) and supports quality standards such as ASCE 38-02 and the imminent ASCE 38-20. It offers permissions-based security to protect the data. The Prostar system integrates with Colorado 811 in real-time, making it possible to display the location of all open tickets and their status on a PC or mobile device such as a tablet or smart phone.

Pointman handheld app

The primary goal of the system is to provide easy-to-use access to high quality location data at low cost and to fit into the existing engineering and construction practices or network operators to minimize the learning curve and avoid adding to costs.  Pointman is free and offers an affordable handheld solution for small contractors.  The Transparent Earth server application is available to network operators, large construction contractors and engineering consulting firms, and government agencies such as CDOT.  It enables all stakeholders in a construction project to share data about underground infrastructure.

Another advantage of the system is that it enables survey-grade information to be captured by survey technicians as well as GIS professionals with some additional training in survey technologies.

Pointman can be paired with a number of devices including RTK for survey grade location determination and GPR and EMI underground scanning devices to provide a record of SUE locating. Furthermore, relocations of existing utility infrastructure can be captured with the Pointman handheld app during construction.

The new legislation differs from previous legislation by explicitly making the State of Colorado, through its agency CDOT, responsible for regulating infrastructure installed in the the public right-of-way.  In practice every network operator that plans to install network facilities in the public ROW, is required to apply to CDOT for a permit.  One of the requirements of the permit is that for all newly installed facilities network operators must ensure that the the new facilities are locatable, either by marker balls and tracer wire and by an accurate survey.  Furthermore, within 45 days of the completion of construction the network operator is required to provide "as-constructed" plans in PDF format to CDOT. The as-constructed document must comply with the ASCE standards 38-02, which specifies quality levels A through D, and 38-20, which specifies seven accuracy levels ranging from Level 1 ( XY ± 50 mm, Z ± 25 mm ) to Level 7 (indeterminate).  

As-built data submitted to CDOT (red line) and CDOT quality control survey (blue line)

The real teeth behind the permit system is that it mandates CDOT to conduct quality control as part of construction oversight.  Specifically it requires third party inspectors registered with CDOT and paid for by the network operator to conduct construction oversight to ensure that the "as-constructed" PDFs submitted to CDOT accurately reflect what was actually installed in the ground.  Various measures including denial of further construction permits and civil penalties can be levied against non-compliant network operators.

In summary this is a ground-breaking initiative involving legislation, regulation and new technology to address one of the chief causes of highway construction delays and cost overruns. CDOT's solution is now getting the attention from other state DOTs as well as several Federal agencies.  For example, Utah DOT has followed CDOT and has implemented the ProStar Solution.

The role of surveyors in locating and mapping underground utilities

Accurately mapping underground utility and telecom network assets represents a growing opportunity for professional surveyors. In order to ensure continuing improvement in the accuracy of location information about underground utilities, some international jurisdictions are requiring that new or modified underground infrastructure be surveyed by a registered surveyor. Technical advances are making it easier for surveyors to conduct underground surveys. For construction projects owners, engineers and contractors are increasingly recognizing that surveyors who can offer a combined above- and below-ground survey are able to add significantly more value than the traditional above-ground-only survey.

Technical advances enable surveyors to conduct underground surveys

Utility locating involves remote-sensing and safe excavation technologies for identifying, detecting, and labelling underground utility infrastructure including telecommunication, storm and sanitary sewers, water, electricity distribution, natural gas, cable television, fiber optics, heating and others. Underground locate practitioners use all the information that is available to them including as-builts (however unreliable), site surveys, remote sensing tools such as electromagnetic induction, ground penetrating radar, and other techniques, and potholing. Industry standard tools are electromagnetic induction and detection (EMI), which can only detect metallic objects and has limited vertical accuracy and ground penetrating radar (GPR) which can detect nonmetallic objects and provide 3D location, but is not reliable with certain soil types. Until recently interpreting GPR scans has required a trained geotechnologist, which has limited the adoption of GPR by surveyors and other potential users. Furthermore, most EMI and GPR devices are intended to operate at a walking pace making them dangerous and inefficient for large scale surveys. Recently there has been accelerating innovation in advancing technology for detecting underground infrastructure by startups and by established firms such as Leica Geosystems and Bentley. Recent advancements to the remote sensing technologies commercially available for detecting underground infrastructure are enhancements in GPR and the development of inertial locating and acoustic surveying.

Traditional output from a GPR scanner showing hyperbolas reflected from underground utilities

A major inhibitor to broader use of ground penetrating radar for detecting the location of underground utilities is the difficulty in interpreting radar scans. non-geotechnical professionals including surveyors found it a challenge to interpret GPR scans consisting of images with hyperbolas showing the reflections of RF waves from underground objects. GPR remained the preserve of highly trained geotechnical and other underground engineering professionals. In 2019 Leica Geosystems released the DSX ground penetrating radar system that is the first to address this gap in a compact, portable system. As a result of the growing interest among the surveying community to expand their professional offerings to include above- and below-ground surveys, Leica Geosystems is focusing on simplicity with its latest GPR devices and software.

Output from the DSX with DXplore software showing tomographic image of detected underground utilities

A key feature of the DSX GPR device and DXplore software is analytics to interpret the GPR scans and visualize underground infrastructure in the form of tomographic images, rather than radar hyperbolas. For accurate locating the DSX supports seamless integration of positioning sensors (GNSS antennas) and is the first device to be integrated into machine control workflow through avoidance zones based on an underground utility map generated by the DSX. In a semi-outamted process software processes captured GPR images are used to idenitfy the location of underground cables and pipe. The resulting 3D model can be exported as a 2D or 3D vector file in a CAD compatible file format.

This may not be useful for experienced GPR practitioners. Geotechnical experts are trained to work with B-scan/radargram data representation and interpretation. But for surveyors and others who don't have GPR experience and recognize that underground surveying represents a significant business opportunity, this represents a way to incorporate underground surveys underground into their practice.

Requiring a survey crew to be on-hand throughout an excavation to survey exposed utilities can be cost prohibitive. A research project by Costain and Bentley found accurately surveyed contral points enabled photogrammetry using a consumer grade smartphone can generate a 3D model of comparable accuracy to a traditional survey and is much more cost efficient. It was shown that a simple workflow is adequate to capture enough information with a smartphone to accurately determine the location of underground utilities.

1. Mark ground control points (GCPs) around the area. They have to be visible in the pictures taken with the smartphone.
2. Take pictures from varying angles and heights around the exposed utilities with a smartphone.
3. Survey the GCPs with a total station, at least three are needed to accurately determine the location of the 3D model created from the pictures.
4. Upload the photos taken with the smartphone and process them and GCPs together to create a georeferenced 3D model of the exposed utilities.

This process has been found to result in a 3D model of comparable accuracy to traditional survey and after the control points have been surveyed it is something that anybody can do. Typically it involves taking 40-60 pictures with an ordinary smartphone. After uploading the pictures, processing them with Bentley's ContextCapture software to create the georeferenced 3D model, the resulting 3D model can be made available to others on the construction project using an online web link that allows the 3D model to be displayed along with existing 2D utility as-builts.

To visualize the location of underground infrastructure in 3D mixed reality applications are available from many companies. A recent example that is dedicated to construction is Trimble’s SiteVision. It not only enables visualizing above and below-ground infrastructure, but also allows accurate measurement of positions and distances between objects.

Capturing accurate locations for new and modified underground infrastructure

In order to ensure continuing improvement in the accuraty of location information about underground utilities, some international jurisdictions require that new or modified underground infrastructure be surveyed by a registered surveyor.

Canada

A Professional Surveyors Canada report recommends requiring that all new underground infrastructure be surveyed and mapped in 3D with high precision and reliability and sharing basic information on the type, location and depth of underground infrastructure in a standardized form through a common, accessible system. It is also recommended that all underground infrastructure surveyed should be in a common format that can update a master map/GIS data set. 

Singapore

In Singapore the standard guidelines for new installations of underground infrastructures specify that new underground assets should be surveyed by a registered surveyor using total station, RTK or laser scanning devices. There are special provisions for using inertial locating for assets installed by trenchless digging.

In August 2017 the Singapore Land Authority (SLA) released a standard and specifications for the procedure and practice of utility surveying in Singapore. The Standard and Specifications for Utility Survey in Singapore has progressively been included in contractual agreements for all newly built utilities by utility regulatory authorities. The standard is for open trench cases only. It covers the surveying technologies to be employed, the data to be captured, and specifies that a qualified professional (a Registered Surveyor at the Land Surveyors Board of Singapore) is required.

The standard specifies the data that should be captured for new underground utilities including telecommunication, sewerage, water supply, electric power, gas, and drainage. It specifies that after installing utilities and prior to filling the trenches an as-built survey should be performed by a registered surveyor to capture the location of the utilities with horizontal accuracy of ±100mm and vertical accuracy of ±100mm. It specifies that the survey equipment to be used should be a total station, GNSS Real Time Kinematic (RTK), or 3D Laser Scanning.

This standard is not mandated by the Singapore Government but is intended to provide a baseline to be incorporated in construction contracts. Since 85% of land is owned by the Singapore government, if a major government agency such as the Urban Redevelopment Authority (URA) routinely incorporated this standard in its contracts as part of standard procurement practice, it would effectively become a de facto mandate.

In addition to location, the standard also defines the attribute information to be captured. For example, for an electric power cable, the standard specifies that x,y,z should be surveyed at 20 meter intervals for a straight line cable and more frequently for a curving cable. In addition, height, width, number of columns, number of rows, number of ducts, number of cables and quality level should also be captured. The quality standard used in Singapore is; 1) ±100mm, 2) ±300mm, 3) ±500mm, 4) Unknown accuracy and 5) Trenchless method. In Singapore most underground utility work is open trench, although there is some trenchless which requires gyro surveying.

The standard does not specify format or what is to be done with the as-built information. Currently in Singapore there is nothing in place to require sharing of information about the underground like Netherland's BRO or the British National Underground Asset Registry (NUAR) project. But there is a Digital Underground project underway to create an ecosystem for a digital twin of the underground as part of the Mapping Singapore in 3D project. The digital underground project was initiated by the Singapore Land Authority with the support of the Urban Redevelopment Authority. The standard for underground utility surveying would create a basic data model for sharing information about underground utilities.

France

In France, contractors are required to survey all new and changed underground structures. These surveys must satisfy certain conditions. Location coordinates of structures in an open trench must be surveyed by a certified surveyor. If remote detection technology such as GPR is employed, the firm performing this work is not required to be certified, but a certified surveyor must be involved in georeferencing the data. Whatever the method of measurement used , direct or remote, the accuracy of the locations of new or changed structures reported by the contractor must be accuracy class A, in other words 40 cm or better. For each structure the data recorded must include the name of the project manager of the site, the name of the company that provided the location information, the name of the certified surveyor responsible for determining the location of each structure, the maximum measurement uncertainty (for x, y, and z ), and in the case of remote detection such as GPR or EMI, the type of measurement technology used.

Bern

Bern, Switzerland has instituted regulations to ensure that accurate data is captured for new construction projects involving underground infrastructure. For example, there is a 24 hour rule that requires a contractor to notify the city survey department 24 hours before closing a trench. For large projects city surveyors periodically verify surveys of underground works.

Calgary, Alberta

The City of Calgary has legislated a by-law that is designed to share information about underground utilities and improve the quality of this information. The by-law requires all network operators with underground infrastructure under public rights-of-way to submit to the city electronic as-builts showing the location of newly installed network equipment. The bylaw requires that each network operator submit digital as-built drawings to the City within 60 calendar days following completion of installation of its equipment on a public right-of-way. The as-builts are required to comply with two key provisions

• The equipment is less than 35 centimeters horizontally and vertically from the centre line approved in the utility alignment permit
• It adheres to the CSA S250 quality standard.

Furthermore, the City reserves the right to carry out on-site inspections to verify submitted as-builts the cost of which is shared between the network operator and the City.

Conclusion

In order to ensure continuing improvement in the accuraty of location information about underground utilities, international jurisdictions are requiring that new or modified underground infrastructure be surveyed by a registered surveyor. Technical advances are making it easier for surveyors to conduct underground surveys. For construction projects owners, engineers, and contractors are increasingly recognizing that surveyors who can offer a combined above- and below-ground survey are able to add significantly more value than the traditional above-ground-only survey. Surveyors who offer combined above and below ground surveys are finding that a combined offering increases their profit margins.