UAV PHOTOGRAMMETRY
DRONE MAPPING & 3D MODELING
We have invested in new UAV technology. It may look like a toy, but what can be done with these is truly amazing. We have the DJI Phantom 4 RTK which has a dual frequency GNSS receiver and a 20M camera. It is capable of capturing hundreds of high resolution aerial photographs in a single 30 minute flight. Those photographs are feed into digital photogrammetry software (Agisoft MetaShape) and processed into 3D models or high resolution aerial orthomosaics which can be very accurately georeferenced and be used seamlessly with existing field surveys.
APPLICATIONS
One of the most obvious applications for this technology is computing stock pile volumes in large gravel pits or construction sites. With proper procedures stock pile volumes and topography can be done almost as accurately as traditional surveying methods, in a fraction of the time, with the added benefit of high resolution photographs of the entire site. The old adage "a picture is worth a thousand words" has never been so true.
AERIAL PHOTOGRAPHS
Aerial photographs of large areas can be processed from hundreds of drone photos by modern digital photogrammetry using computer vision algorithms. These aerial photographs are stitched together and orthorectified to remove camera tilt and terrain relief and result in an image with a constant scale throughout.
Depending on desired relative or absolute accuracy of the resulting image a survey grade GPS receiver can be mounted to the drone, ground control targets can be placed, or the low accuracy drone GPS can be used. All of these methods will result in a beautiful high resolution image.
SAMPLES
This orthophoto was processed from 212 overlapping images flying at an altitude of 400 feet. Total area shown is about 100 acres. This was flown with the Phantom 4 Pro.
Camera Calibration Site
In order to produce accurate data the UAV camera must be calibrated with a large number of ground control targets. This is critical if using a drone equipped with a survey grade GPS receiver which is used to reduce or eliminate placing ground control. While relative elevations may still be reasonable, absolute elevations will suffer with a poor calibration.
This calibration site had 15 ground control targets accurately survey with a Trimble R10 and on site R8-4 base. The Phantom 4 RTK drone having a dual frequency GNSS was post processed against the same R8-4 base. The lever arm 3 dimensional yaw, roll, pitch corrections from the GNSS antenna to the camera nodal point were corrected with GeoAdjust (in house developed software).
All 239 camera coordinates and all 15 ground control coordinates were held with reasonable error estimates to produce the calibration. The report below shows how accurate drone photogrammetry can be.
Phantom 4 RTK Calibration Report
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Brownville Village
This site was flown with the Phantom 4 RTK using on site Trimble base station. The drone GNSS was post processed with an on site Trimble R8-4. Antenna to camera 3d rotations were applied with inhouse developed software. Three ground control check points were set for verification.
