Hey everyone,
I know this has likely been covered but hoping someone can point me in the right direction.
Im getting a massive error in vertical when shooting GCPs with the RS2+, I understand it could be something to do with ellipsoidal and geoid heights. Can anyone offer me some guidance on how to solve this issue the simplest way possible (if that exists 
)
Thanks
James
Hi James! Did you load the GEOID in project setup? If not just setup a new project, shoot in a point you already captured, adjust you points in Excel and then import them into the new project or just utilize them as you initially intended. If you no longer have access to the site you can apply a standard GEOID height offset but the larger the project the more you are going to be out of relativity across the board.
Hi Michael, I didnt load the GEOID in project set up unfortunately. Im in the UK, do you know which GEOID profile I would need? I have all my points so I am hoping I can just offset the verticals with a standard offset as you said Im just not sure how to do that or which way is the easiest.
Thanks
If the area you surveyed is fairly small, within 1-2 km, you can indeed apply a constant offset on every ellipsoidal height and keep the centimeter accuracy.
You can use the official coordinates transformer tool here on one central point of your survey and derive the offset from the results.
Use ETRS89 decimal degrees as input.
I could guess based on your location but I am sure someone on here is more familiar with your datums.
For the most part you are correct but it depends on the GEOID and the amount of relief on the site, but as you eluded to anything less than 50 acres or so is probably pretty safe with GNSS.
Thank you Florian, I am not a surveyor so this is a bit outside my area of expertise. Could advise me the coordinate system I am using is ETRS89 / Jersey Transverse Mercator - can you advise when inputing the coordinates I am getting an error message. Thanks
Thanks Michael, are you able to offer me some guidance on converting the ellipsoidal heights into geoid heights and which geoid profile would suit my location? Coordinate system used is ETRS89 / Jersey Transverse Mercator. Thanks
Where are you seeing the elevation difference? Is it in SFM software? What software are you using? Are your drone images geotagged with the drone’s WGS84 coordinates or is the drone using a local vertical datum?
So in the DTM I am seeing a large difference in elevation, I am using a pr4rtk but have disabled the image geotagging and am using only control points for georeferencing the scene. I am using Reality Capture but I need to download the correct datum to in Emlid Flow to offset the vertical errors in the points and I am unsure which datum to go off.
Hi James,
I also wanted to add a couple of words. Emlid Flow supports several geoid models for the UK. You can check them here. The exact geoid you need depends on your project and is usually specified in the technical task.
You can use the OS-Net service to convert the data for the points you have already collected. I see that Florian has shared the link to it. You’ll need to use the geographic coordinates of the collected points. If you have worked in ETRS89 / Jersey Transverse Mercator, they are in ETRS89.
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