|Job Type||Surveying a Historical Monument|
|Project Date||April 2014|
|Project Size||7 acres (170m x170m)|
|Camera||Nikon Coolpix S6500|
|Flight Altitude||75m (246ft) & 130m (426ft)|
|Accuracy||better than 2 centimeters (5-6 hundredths of a foot)|
|DatuSurvey™ Savings||1.5 days|
The required task was to survey and draft a 3D CAD plan, with a measurement accuracy of better than 2 centimeters (5-6 hundredths of a foot), of a pedestrian bridge.
Original Effort Estimate
The original effort estimate for the surveying project, using conventional surveying techniques, was two days. This appraisal was based on one day in the field, using a Total Station device from two different stations, and one day in the office to draft the detailed CAD plan of the bridge based on the Total Station measurements and the sketch done in the field.
DatuSurvey™ ( DatuGram™3D) Processing
The actual time to survey the bridge and prepare a 3D CAD model was less than six hours. The time spent in the field was 30 minutes: 10 minutes to photograph the foot bridge, and an additional 20 minutes to measure several control points on the bridge. The bridge was photographed with a regular Nikon Coolpix S6500 camera (15-megapixel resolution) with a 5-mm lens.
A total of 36 images of the bridge were captured from the perimeter of the bridge toward the center, with an image taken about every 10 meters (30 feet). To minimize foreground obstructions in the images and expedite fieldwork, the camera was mounted on a small quadcopter that flew
at an elevation of 35 to 45 meters (120 to 150 feet) above the ground. These images were combined with images taken at ground level.
A total of 20 points were measured using a prism-less Total Station device; 10 of these points were used as control points for the geo-referencing
of the images. The actual time in the office to geo-reference the images and draft the 3D CAD plan of the bridge directly on the images was about 5 hours.
A 3D CAD model of the bridge in DXF format was generated by drafting directly on the oblique images using DatuSurvey™ ( DatuGram™3D) . In addition to the DXF file, a list of all measured points in PNT format was generated. This included the point names, codes, descriptions, coordinates, and their measurement accuracy in all axes. In total, 135 new measurements were made from the images. The measurement accuracy of all points was better than 2 centimeters (5-6 hundredths of a foot) in both position and elevation.
The survey in the field using a regular camera mounted on an UAV proved to be rapid, effective, accurate and, furthermore, much safer, compared to surveying using conventional techniques. Overall, the surveyor saved significant field and office time – from one day to only half hour in the field, and from one day to only 5 hours in the office.