Just wondering how to measure height of each spot after processing map or do any function to let us measure each spot height from sea level?
You might check these documents out on that on the FAQ page.
Am I right in saying that for example, if there was a wall height that you needed to measure from the map, you would use the measurement tool to draw a straight line at 90• across the wall, and then get the height measurement from the elevation profile? Keeping in mind that ground zero (0m) is the take-off location of the drone.
You use the calibration tool to set the elevation of the whole map according to a point that you know the exact elevation for. You can then use the location pin or the distance measurement to get elevations.
In the past when I have calibrated the map, I have recorded the “take-off” point as “0m” for the height. For the most accurate information, does it matter that the camera is actually 10-20mm off of the ground?
If I use a GCP as my “take-off” point, do I need to take into account the distance from the ground/surface to the centre of the camera, even though it is a few mm?
That should actually be measured from the GPS sensor which is at the top of the Drone. Wherever you take off from and the altitude that you’re flying at is 0. If you have a known Benchmark or something with an elevation on the map you can use the calibrate tool which is in the top header project information to adjust the entire map to that known point.
is there any video clip sample or youtube link can share to me?
No video, but maybe this will help. Once you calibrate the rest of your map elevations will be adjusted accordingly. Not as accurate as setting elevations with GCPs, but an easy way to get relatively close to real-world elevations.
The location marker annotation gives you coordinates and the spot elevation.
@Michael: Just an observation: A P4P does not use GPS to measure elevation. It uses its on-board barometer which is also near the top of the drone. The barometer is up to 10 times more accurate than non-RTK GPS for relative elevation measurements.
@waynecoomer : Once you create a map with DD the elevations are relative values. If you ask DD what the elevation of a spot is and then use the calibrate tool to set it to a new value, details like the position of the camera are irrelevant. All such offsets are already baked into the elevation reported in a DD elevation measurement. It would be double counting to put them in again. As you move away from your calibration point, then error will creep into your elevation measurements. To reduce the error you will need to use multiple GCP’s when you fly the mission. These can be used during the photogrammetry step to create the 3D model with much better 3D accuracy.
Hey guys, interesting information and thanks for the replies. Never too old to learn!