Scope: Topographic Scan of the east dam abutment including the E7 Joint.
Date: July 2002

Project Facts:
Field: 4 days, 2 person crew; 120 scans

Office: 4 days; 1 person

Deliverables:AutoCAD plan drawings with topographic contours at 1' intervals; AutoDesk LDD 3D points and surfaces accurate and repeatable within +/- ½ inch. Established 6-10 permanent targets to be used as surface registration upon repeat scans, Power Point presentation for internal illustration/demonstration, traditionally verified permanent targets both horizontal and vertical; all points to be shown in state plane coordinate system.

Benefits of 3D Laser Scanning

• Traditional survey crews were not required to repel off cliff faces to acquire data points on inaccessible areas
• A four fold increase in field productivity compared to traditional survey methods
• 25 times more points were collected over surfaces that were inaccessible with detail that simply could not have been acquired by traditional means
• Repeatable and comparable surfaces to verify movement with ½ an inch

Project Background:
The United States Bureau of Reclamation operates a dam safety program which includes extensive and varied monitoring tests. ArrowSCAN, Inc.(ASI) -Boise, Idaho has successfully completed 3D scans of a landslide area for the Pacific Northwest Region- Boise Office and was awarded the Deadwood Dam scanning and surveying project. The Deadwood Dam is located approximately 100 miles north of Boise, Idaho on the Deadwood River, a tributary of the Payette River and subsequently the Snake River. This arch style dam was built in 1930 for the purpose of providing irrigation storage and recreational facilities. It is 160 feet high and approximately 320 feet wide with a spillway elevation of 151 feet. Safety concerns exist on the east abutment of the Deadwood Dam and specifically a geological joint labeled E7. The dam safety group continues to monitor this area closely. One of many actions taken to increase dam safety was to acquire an accurate and detailed baseline topographic map. This data needed to be repeatable, accurate, and detailed enough to determine small movements and geological volume shifts or differences when compared to subsequent scans of the same area.

Workflow:
ArrowSCAN, Inc. made a pre-scan site visit to determine distances and develop a plan for target placement and utilization. This site visit included coordination with a Bureau geologist and engineer regarding permanent target placement outside of construction areas and other site work. ArrowSCAN, Inc. determined to use existing 2 inch diameter pipes drilled into the abutment and located in areas that were visible from various scanner locations. This process was aided by the use of an Impulse range finder to quickly tell the distances between estimated scanner and target locations. ArrowSCAN, Inc. planned to use 5 or 6 scanner locations with approximately 10 scans each.

ArrowSCAN, Inc. arrived a week later to commence work. The first task was to setup 11- 6 inch diameter hemispherical targets and 4- 6 inch planer targets. The first scanner location was on an access road to the valve house at the bottom of the dam. ArrowSCAN, Inc. then moved down the access road giving a significantly different angle to the abutment. The next day the scanner was setup on the top of the dam and scans were made of the same abutment from three different locations on the top of the dam. This work method allowed complete coverage of the entire embankment thus preventing any non-scanned or shadow areas (black holes). The completed scans were then registered or combined together using the hemispherical targets. The targets were registered between 0.002 feet and 0.020 feet of each other. The point separation was an average of 0.3 feet with a total of 640,000 points. This provided a detailed multiple scan for the deliverables requested.

A survey utilizing a Trimble 4700 GPS system was performed which acquired state plane coordinate information from Scott Mountain monuments approximately 15 miles away from the Deadwood Dam. The survey included the permanent points used in scanning plus three additional monuments set by the Bureau. The scanned points were then registered to the survey thus making the entire scan and permanent targets match the state plane coordinate system. As a vertical check a conventional level loop was performed.

ArrowSCAN, Inc. Deliverables:
The registered point clouds were reduced in quantity to 5493 points via mesh decimate and virtual surveyor commands. These points were then converted for use in AutoDesk LDD 2000 or Land Desktop3. The point data once in AutoDesk was used to generate surfaces and subsequently contours at 1 foot intervals. A topographic drawing was made of the E-7 Joint abutment and plotted using state plane coordinates and sea level elevations. The point clouds were also converted into surfaces and a Cyclone software "Viewer" was provided for raw Cyclone point and surface viewing by Bureau employees. Numerous digital photos were taken both from the built-in scanner camera and a separate digital camera. These photos as well as point cloud photos were provided as well as a sample Microsoft Power Point Presentation of the scanning project for internal presentations.