Calibrating Flights to Each Other (no GCP's in original flights)

Hello everyone! This is my first post here and I’m asking because I am stuck.

I’m an experienced drone pilot but have run into an issue exporting and creating a Digital Elevation Model on a site that we are trying to convert to both shapefiles for ArcGIS and AutoCADD and create engineering plans to design plugs to install in channelized ditches – essentially the same thing as damming a river on a much smaller scale. To engineer the size and dimensions of the plugs and accurately model hydrology, you need elevation and dimensions of the channel itself and the surrounding land’s elevation (floodplain and watershed). Makes sense right?

BACKGROUND: I flew several missions on the same property with a Mavic 2 Pro and no GCPs. Some mission polygons overlap and some do not. In exporting the DEM as shapefiles (ArcGIS) and AutoCADD, each mission has different +/- elevation data since the drone had a different take-off point for each mission and DD captures elevation data relative to the take-off location rather than sea level. Since -10 feet elevation on one mission may be the same absolute elevation as +35 feet elevation on another mission, our engineer using AutoCADD cannot calibrate each mission’s elevation data to the others and so we can’t get a single big-picture dataset to capture all the elevation data taken and make a DEM that has absolute accuracy.

SOLUTION?: I think I have a work-around, but I’m not sure if it will work. The idea is that adding in an elevation point or two (GCP’s) per mission in DD using the Calibration tool will give each mission absolute accuracy by calibrating it to the surface of the earth. If each mission has absolute accurate tied to the surface of the earth, then all the missions (datasets) will be calibrated to each other by means of each being calibrated to the earth’s surface. Will that work?

Welcome! For engineering hydrology they should be using GCP’s. DroneDeploy is supposed to automatically align maps but ours have not been working lately. It is a sticky situation because ours missions are split into 1/3rds of GPS, GPS/GCP and RTK and while they are close they’re are not close enough for grade critical work.

It sounds like they have plenty of relief (elevation change) but when you get to lower relief every 0.10ft counts and when your map’s relative accuracy is +/- 1m/300m drainage studies get very sketchy. If you can find a way to use GCP’s they don’t have to be perfect, just repeatable.

Thank you for the quick response! My question is if we can just add an elevation point to each of the already-flown missions in DD to calibrate the data rather than fly it again using GCPs.

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It does have a single point elevation calibration in Map Details but without GCP’s you are still going to have quite a bit of relative error. We need to get DD to look at the alignment tool. Can you see that section in the processing report.