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Hi Everyone Sorry this is a long message. I've tried to give as much detail as possible to help with replies. I’m stuck and any assistance would be much appreciated! I’m processing Phantom 4 rtk data collected whilst connected to a d-RTK 2 DJI base station in Metashape Professional 1.6.2 and getting large z errors in one of my data sets and can’t work out why or how / if it can be solved. Ultimately I am going to export the DSM into ArcGIS to calculate volume of soil loss in the gulleys that are present across the bare earth fields using an ArcGIS toolbox. My normal workflow is to install a ground marker for the base station, survey its location with Trimble R10 with real-time corrections via VRS. The Trimble was set to survey in OSGB OSTN15. I look at coordinates of the point on the Trimble, after converting them to WGS84 lat long in decimal degrees (for the P4 rtk controller). Set up d-RTK 2 base station over the known point just surveyed. Put out markers and survey in their location with the Trimble R10 (still set as OSGB OSTN15). Start up P4 rtk and controller and base station, input the known coordinates into the controller, but first adding 1.802m to the z value to account for the base station DJI pole and save (using the settings button), fly with rtk on and connected to the base for corrections. Fly the pre-programmed flight path using 2D and/or 3D photogrammetry options. Add photos into Metashape including XMP data, align photos, use gradual selection to remove some of the noise in the data. Check box in camera calibration to enable rolling shutter compensation. Export coords of markers from Trimble in WGS84 lat long decimal degrees csv file. Import markers into Metashape, filter photos on each marker, one at a time and drag flag into centre to locate. Check reference settings coordinate system is WGS84 (EPSG::4326). Camera accuracy set at 0.03m. Marker accuracy set at 0.01m. All markers and cameras are left ticked for the following step. Optimise cameras using adaptive camera model fitting. This normally gives v good accuracy, e.g see the first attachment. But with the problem data set, collected on the same day as the one above, over bare earth fields, I’m getting much larger errors in the z field. See the 2nd attachment – errors in the x and y for the gcps about 2cm, but 35cm in the z. I flew this at 2 altitudes, one using the 2D option (nadir only) at a height of ~30m, the other over a smaller subsection of the field with gullies using the 3D option (oblique) at a height of ~25m. I’ve tried with both sets separately and one combined file as well (which has 2175 images). I get these errors with all options. If anyone has any suggestions on how I might be able to improve the z value, sources of such large error or whether this will be as good as it gets with this data set I would be very grateful. I’m just scratching my head why this data set is so poor with the z values when I can get good results at other sites with the same workflow. Many thanks in advance.
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