Indianapolis Lidar Project

Indianapolis Lidar Project

Indianapolis LiDAR (Light Detection and Ranging) Project

Contracting Agency: Marion County Information Services Agency, for IMAGIS

Geographic Coverage: Marion County, Indiana + 1-mile collar (~500 sq. mi.)

Time Period: March & April 2003.

Map Data: Coordinates are in Indiana State Plane East (NAD83, NAVD88), in International decimal feet.

Contractors: GRW, Inc. (Lexington, KY) and Laser Mapping Specialists, Inc. (Raymond, MS). GRW was the prime. LMSI flew the LiDAR mission and corrected the point cloud to ground control. GRW stripped the cloud to make the bare-earth model, and built the DEMs.

Flight Mission: The LiDAR flight was conducted by LMSI in a Cessna 337 push-pull twin-engine aircraft. Flight height was 2,700 feet AGL; flight speed was 150 Kts. Flight management was done with the ALTM-NAV System showing real-time navigation and swath coverage display.

Flights utilized airborne GPS and an Inertial Measurement Unit (IMU), a gyroscopic tracking device in the airplane. During each flight, simultaneous ground station GPS data was collected.

For the whole county plus a 1-mile collar, LMSI captured 136 flight lines, east-west, single-pass (50% sidelap), 1 point per square meter (on average), first and last returns plus intensity.

For 4 square miles of the downtown they also captured 16 flightlines at ~45 degrees offset from the east-west flights (also with 50% sidelap) at 1-meter spacing, first and last returns, plus intensity.

LiDAR Sensor: Optech ALTM 2033. This device collects 33,000 points per second in an oscillating (zigzag or saw tooth) pattern, perpendicular to the flight path.

Post Processing: Initial QC was done with the REALM Post-Flight Data Processing Software. The point cloud was adjusted to an analytic triangulation solution of 50 first-order ground control points. Final accuracy of each LiDAR point (root mean square error) is 6-inch vertical and 1-foot horizontal. This is sufficient for controlling orthophotos and calculating 2-foot contours meeting ASPRS Class 2 standards for 1"=100' scale maps.

To be useful for building a digital terrain model to control orthophotography and to calculate ground contours, the non-terrain features (trees, buildings, etc.) were removed from the full point cloud to form a bare-earth surface.

For the orthophotography surface, the bare-earth surface was regularized into a 25-foot grid DEM. For the 2-foot contour surface, the bare-earth surface was further manipulated into a 10-foot grid DEM, and breaklines were added at severe changes in terrain.