Case Study: Surveying Stockpiles, Phoenix, Arizona Date: October 2014 Location: Phoenix, Arizona
The Survey The required task was to survey several stockpiles in order to calculate their volume, with a measurement accuracy of better than 5 centimeters (15-16 hundredths of a foot).
Original Effort Estimate The original effort estimate to survey the stockpiles and calculate their volume using conventional surveying techniques was 2.5 days: 1.5 days in the field, using a Total Station or RTK device, and one day in the office to create CAD models of the stockpiles based on the Total Station/RTK measurements and subsequently calculate its volume. Fieldwork using conventional surveying techniques involved major occupational safety challenges due to the need to ascend the stockpiles carrying the Total Station/RTK device in order to measure specific points.
Actual Time Using DatGram™3D The actual time to survey and create an accurate 3D CAD models of the stockpiles totaled only 3 hours. Fieldwork totaled only 1 hour: 40 minutes to mark and measure several control points around the stockpile, and 20 minutes to photograph the stockpile. The stockpiles were photographed with a regular Sony ILCE6000 camera (24-megapixel resolution) equipped with a 16-mm wideangle lens. The camera was mounted on a small quadcopter and remotely controlled. A total of 25 images of the stockpiles were taken, from the perimeter of the stockpiles towards their center, from an elevation of about 35 meters (120 feet) above ground level. A total of 10 points were measured around the stockpiles using a prism-less Total Station device; six of these points were used as control points for the geo-referencing of the images. The actual time spent in the office to geo-reference and automatically create accurate 3D CAD models of the stockpile was only 2 hours.
Results Less than an hour was required for DataGram™3D to automatically generate 6,874 topographic points on the stockpiles and connect them into meshes. The measurement accuracy of all the points was better than 5 centimeters (15-16 hundredths of a foot) in both position and elevation. The mesh of topographic points was exported in a standard DXF format to CAD software to calculate the volume of the stockpiles. .
Lessons Learned The survey in the field using a regular camera mounted on a UAV proved to be rapid, effective, and accurate when compared to surveying using conventional techniques. Overall, the surveyor saved significant field and office time – cutting work time from1.5 days to 1 hour in the field and from 1 day to 2 hours in the office. Moreover, the field crew did not have to climb the stockpile, thus considerably reducing occupational hazards. Furthermore, the number of topographic points automatically generated by the software and the measurement accuracies significantly surpass the number of points and measurements accuracies that can be generated with total station/RTK on a stockpile.