CASE STUDY: Surveying a Gravel Stockpile, Sau Paolo, Brazil

Date: May 2015
Location: Sau Paolo, Brazil
Customer: Grupo Serveng

Original Effort Estimate
The original effort estimate to survey the gravel stockpile and calculate its volume using conventional surveying techniques was one day: half a day in the field of a crew of two people, using a Total Station or RTK device, and half a day in the office to create a CAD model of the stockpile, 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 stockpile carrying the Total Station/RTK device in order to measure specific points.

Actual Required Time Using DatGram™3D
The actual time to survey, create an accurate 3D CAD model of the gravel stockpile, and calculate its accurate volume totaled at only 1.5 hours. Fieldwork involved only 1 hour: 40 minutes to mark and measure several control points around the gravel stockpile, and 20 minutes to photograph the gravel stockpile. The gravel stockpile was photographed with a Sony NEX-7 camera (24-megapixel resolution) equipped with a 16-mm wide-angle lens. The camera was mounted on a small quadcopter and remotely controlled. A total of 28 images were taken around the gravel stockpile, from the perimeter of the stockpile towards its center, from an elevation of about 35 meters (120 feet) above ground level. A total of 9 points were measured around the stockpile using a Total Station device; 8 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 the images, automatically create an accurate 3D CAD model of the gravel stockpile, and accurately calculate its volume was only 30 minutes.

Results
Only 5 minutes were required for DatuGram™3D to automatically generate more than 4,900 topographic points on the gravel stockpile and connect them into a mesh. The measurement accuracy of all the points was better than 2 centimeters (6 hundredths of a foot) in both position and elevation. The volume of the gravel stockpile was calculated through DatuGram™3D.  

In order to test the accuracy of the volumetric analysis, the gravel stockpile was also surveyed in a conventional method using Total Station (number of points measured was 206). The discrepancy between the volumetric analysis done by the conventional method and the volumetric analysis done from the images was merely 0.32%.

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 from 1/2 day to 1 hour in the field and from 1/2 day to 1/2 hour 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 measurement accuracies that can be generated with a total station/RTK on a stockpile.

Note: Setting fixed control points around the stockpile site can eliminate the need to measure again control points when the site is revisited, thus reducing the fieldwork to only.

For More information please visit http://www.datumate.com/

To purchase the software please visit http://www.neigps.com/product/datugram-3d-license/