Lidar for i 15 design

Project Report Evaluate Use of the Asset Management LiDAR Point Cloud for Design Grade Survey Project S-I15-8(151)349 Pin 10491 Farr West to Brigham City MP 349.74—MP 362.02 Rod Terry Project Manager, UDOT Region 1

Jefferson L. Searle, PLS Project Manager Meridian Engineering, Inc.

Project Report | S-I15-8(151)349 | 2700 North (Farr West) to 1100 South Brigham City) | June 7, 2014

Asset Management Point Cloud for Design Grade Survey in time to set targets before the project area was scanned.

After the successful use of the asset management point The I-15 project did not have these targets available for cloud on a 6.7 mile stretch of I-80 between Silvercreek and calibration. To adjust the point cloud, objects identifiable Wanship, the use of the point cloud data was in the mobile scans were surveyed by Meridian field crews as calibration points. Working contemplated on several other with an un-controlled or targetdesign projects. less point cloud would prove to The testing of the point cloud be the first major obstacle that data on the stretch of I-15 was overcome during the course Not Surveyed between Farr West and Brigham of the project.

City, in Box Elder County, Utah

Project Introduction

This obstacle was overcome early on for the southern 2.2 miles of asphalt-paved roadway. Both northbound and southbound sections were registered using striping as registration targets.

The next challenge identified by the team was the restriping that took place on the remaining ten miles for each travel direction.

This challenge was overcome by doing small registration scans with a survey grade terrestrial scanner. However only the southbound ten miles were free of the third obstacle, which was eventually identified as an anomalous exporting of the northbound data. Overcoming this challenge was difficult but has led to improvements that will enhance future projects utilizing this data.

was agreed to by the project team and notice to proceed with surveying activities was granted July 30, 2013.

Several differences between the I-80 and I-15 project areas and environment have added to the breadth and quality of the point cloud testing. The physical environment of I-15 is made up of long straight stretches of extremely high volume traffic, with little vertical relief in the terrain, running north and south, just east of the Great Salt Lake.

This is in contrast to the comparatively moderate traffic volumes in the mountain canyon environment of I-80. The I-15 project is longer at 12.28 miles between Farr West and Brigham City (mile post reference 349.74 to 362.02). The highway is also paved primarily with concrete, only the southern 2.2 miles are paved with asphalt. Compared to I-80 which is an asphalt roadway.

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I-15 Project Overview

There are two interchanges included in the survey area at SRNot Surveyed 126 (2000 West), and SR-315 The biggest difference between Project Overview Map showing supplemental survey (750 North). There are three the two projects, relevant to the areas and structures surveyed. additional sets of bridge use of the point cloud for design, is the control used to calibrate or adjust the point cloud to structures at 8700 South, 7800 South, 2950 South, four the project coordinate system. On the I-80 project the roadway culverts at 8300 South, approximately 1000 potential for using the cloud was understood up front and North, 3550 South, and Davis Street, in addition to a canal

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Project Report | S-I15-8(151)349 | 2700 North (Farr West) to 1100 South Brigham City) | June 7, 2014

Asset Management Point Cloud for Design Grade Survey culvert. The survey area also included the port of entry and was the dowel bar project. Later after inspection of the a northbound rest area. photo log images collected at scan time (now easily The design concept is for additional lanes to be accessible on UDOT’s webpage through Roadview constructed in the current median both northbound and Explorer) the construction project was verified to have southbound, bridge rehabilitation, and structural changes been completed just prior to the mobile scanning effort. required by the added lanes.

A combination of survey methods were used to collect the project design data.

The pavement survey was to be accomplished using the calibrated asset management mobile LiDAR point cloud.

The bridge surveys were planned to be collected by survey grade terrestrial LiDAR scans (using a Leica C10 scanner).

The median survey was collected primarily by GPS. The outside slopes north of SR-315, ramps, cross streets, minor structures, and the rest area were also surveyed by GPS or total station. The port of entry was a combination of GPS surveys and terrestrial scanning. Scans were of the pedestrian tunnel and entrance areas.

The surveying tasks were broken up into three survey areas. Supplemental Above: Asset management data collection image (MP 356.5). Below: Field inspection Survey Area 1, the southern 7.3 miles image taken during project. Note the dowel bar stitching in both and the striping change. of the project, encompassed a median survey only. Traffic control barrels are visible just off the shoulder in Supplemental Survey Area 2 included a median survey as the scans at the south end of the project area. The striping well as outside shoulders with western frontage road areas however had not been completed prior to mobile for 2.4 miles. The remaining 2.4 miles of Supplemental scanning.

Survey Area 3 was a median and outside shoulder survey The mobile scanning in the project area for the but was limited to areas between the right of way fencing. northbound direction began in North Salt Lake on June 27, 2012. Scanning for that day continued north to the Idaho Timing of Scan, Survey, and other projects state line. Scanning south from the state line to Perry. The During early planning conversations with region staff a collection effort continued south on July 1, 2012 back to construction project that had occurred a few years prior North Salt Lake. Mobile scanning on the ramps was was discussed. During that project dowel bars were placed completed in September of 2012. to stitch together the concrete panels making up the road The control survey began at the beginning of August, 2013. surface. The resulting grouted stitches are visible Terrestrial scans of the bridges were performed in throughout the project area. This project was completed September, 2013, concurrent with the supplemental just before mobile scanning. The striping for this section surveys. Supplemental surveys were required in the was also redone. Originally there was no reason to suspect vegetated areas, specifically the median along the entire that the striping was not completed prior to scanning, as project length, as well as the shoulders north of SR-315.

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Project Report | S-I15-8(151)349 | 2700 North (Farr West) to 1100 South Brigham City) | June 7, 2014

Asset Management Point Cloud for Design Grade Survey The supplemental scans needed due to the restriping issue were performed in November. Additional supplemental surveying to finalize surveying activities (due to an issue discovered during the QC of the northbound scan data) was completed in February of 2014.

I-15 Point Cloud Calibration Early on, the skip lines down the center of both northbound and southbound paved surfaces were identified as potential primary control points. Inspection of the point cloud identified particular skip marks whose corners were clearly visible in the scans. These identified marks were then communicated to the survey crews who shot the specified corners (and a few of its neighbors to be careful). Both the identification of stripes in the point cloud and the surveying of them in the field was a rather painstaking process. The description for control point 168 in the southbound direction was the “SE Corner of the 25th Single White Skip just after Slower Traffic Keep Right Sign on the right side of the RD�. This gives a sense of the effort involved in proper identification

Registration scan at MP 356.5 with terrestrial scanner

of the potential control points. The coordinates of the points were then used to adjust the point cloud, or rather to attempt to adjust the cloud.

During the calibration process a report is generated showing the magnitude of adjustment needed to calibrate the cloud in x, y, z, and GPS time. These adjustment values normally change from point to point. However, the

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magnitudes of points near each other are usually quite similar, and change in a trending pattern. Essentially these values highlight the errors inherent to GPS, the gradual shifting of the GPS constellation, undulations in the geoid model, and the quality of the differential corrections (in this case the AGRC base station network or Virtual

Bridge feature extraction from multi-setup terrestrial scans

Reference System).

The adjustment values from this calibration effort did not present a gradual change or trend from point to point, but was uncharacteristically variable from one position to the next. These variations did not represent major changes or inaccuracies, perhaps those represented by choosing the wrong corner of a stripe in the field or in the cloud. A careful inspection of points surveyed and as extracted made it clear this was not the case.

A special field visit looking critically at the striping, together with an inspection of images collected at scan time found the answer. Perhaps it seems obvious in retrospect, but roadway striping was redone on the concrete portions of the roadway in between the time of the mobile scan and the field survey. With this knowledge it was possible to discover in the field a few locations where the old striping was visible, placed only a few inches from the new stripe. Being very close to the original location, but not the same stripe yielded the noisy, out of tolerance, calibration result.

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Project Report | S-I15-8(151)349 | 2700 North (Farr West) to 1100 South Brigham City) | June 7, 2014

Asset Management Point Cloud for Design Grade Survey In fact, striping on a few ramps and cross streets was also redone, but changes were substantial enough that it was obvious that changes had occurred. Alternate control was then sought for and collected during the field survey.

Rather than hunt or sift through the cloud looking for alternative features to use as control, twenty areas were selected that contained large signs, lampposts, or other features were scanned in the project coordinate system with a survey grade terrestrial scanner. These smaller one or two setup scans together with the six large, multiple setup terrestrial scans of the bridges and other structures were then used to identify features common with the mobile point cloud. These features were used register the terrestrial and mobile clouds together.

anomaly was then field verified, both to extent and to which data set was out of synch, by additional survey observations.

This effect and its causes were debated and analyzed by all parties involved.

UDOT preconstruction, asset management, the project team, Meridian Engineering, Virtual Geomatics, and Mandli Communications.

Understanding if and how something like this could take place is critical to the future use of the asset management data for design.

After significant discussion, and internal analysis of the problem brought forth to Mandli, it was determined that the issue was related to distortion in the projection used during the export of the LAS points. The distortion results from projecting a LiDAR data point a significant distance I-15 Point Cloud Processing away from the origin of the route in question. In this case In the southern 2.2 miles of the project, areas paved with the distance from the route origin was over 350 miles. A asphalt, the restriping did not take place. As a result the new tool for exporting the points was already in striping and other features in the point cloud could be extracted to the existing topo, or survey file.

After sufficient and accurate data was collected to calibrate the remainder of the mobile point cloud, extraction of the required survey features was possible for the remaining part of the project.

After the extraction of the survey features from the point Illustration of anomaly in the northbound asset management scans with inset showing transmission tower just west of the project area. cloud all combined datasets were quality checked prior to development at Mandli and is now in use that modifies the delivery of the final base mapping.

The mobile scans and extracted features were compared origin of the route mentioned above to the location of to direct survey observations, the static/terrestrial scans, each scan at export time. Using the new method, and the mobile scan data from the opposite direction. regardless of the route length, the distance from the origin During this process an anomaly was discovered with the is contained to a very small portion of the route. This northbound mobile scans. The data appeared to be scaled projection issue relates only to the extraction of LAS data, in a cross sectional view to the extent that the road not to the asset management data that was the focus of surface appeared approximately one foot narrower (thirty- the Mandli contract. The asset management data utilized a seven feet wide) than reality (thirty-eight feet wide). This method similar to the localized origin method.

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Project Report | S-I15-8(151)349 | 2700 North (Farr West) to 1100 South Brigham City) | June 7, 2014

Asset Management Point Cloud for Design Grade Survey It is important to recognize that the export of LAS data for use in design or for other uses was incidental to the original scope of asset management contract. Mandli has been helpful where UDOT has attempted and now successfully used this data for two design projects, but never planned for this data to be used in this way.

Certification of the data accuracy is the responsibility of the survey and mapping professionals responsible for the calibration and verification of the data.

Tracking down the source of the anomaly and the reasons it occurred took a few weeks too long for the schedule of the design project. Additional supplemental survey on the northbound section was performed to complete the base mapping within schedule, before the newly exported data was available for calibration and extraction.

allows for needed flexibility in the survey schedules and costs to deal with unexpected issues.

The survey consultant or team needs to have a proactive attitude to problem solving to resolve challenges that have not yet been encountered. For example, it would have been detrimental to the project and UDOT’s relationships with its mapping consultants if the team would have tried to place blame concerning the obstacles overcome during this project. Instead a good dialog prevailed and the project was able to move forward with the necessary data.

A constructive dialog was key in determining what happened, why it happened, and what could be done about it.

Lessons learned With the second generation of asset management scans wrapping up, it will be possible to quantify how many changes occur to the system. This will impact when a project may benefit the most from utilizing the scan data for design.

A field inspection of the roadway in comparison to the collected images (Roadview Explorer) is recommended to verify where changes to the roadway have occurred. These changes could be the result of regular maintenance activities, construction projects, accidents or other circumstances and may not be known to the project team.

Changes to the roadway for a project with registration targets may require supplemental survey in areas of change. Changes to a project without targets could impede the registration process.

Having targets painted before scanning takes place is clearly the ideal method. Calibration of scan data without targets clearly is possible, however, it requires more effort from the surveying team. The identification of features useful for scan calibration and the effort involved in communicating the location of these features to the field crews should not be underestimated.

Early projects should plan for some flexibility in their survey schedules and costs to deal with the unexpected.

Consider using an RPLOQ rather than direct select if estimated costs are close to the contract dollar limits. This

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