I know this subject has been touched on in various threads on here, but I am still having trouble wrapping my mind around a workflow/solution.  I understand the P4RTK uses WGS84 EGM 96. I would like to get my DSM into a state plane coordinate system (which I can do) with the correct z value.(which I haven't been able to do) The difference is just a bit over 30m.  I know I must be missing something very simple, and I will probably feel silly after someone points me in the right direction, but it's how we learn I guess!

Anyway, a few other details:

I use Pix4D as software.

I use a nearby CORS station for corrections.

The XY values are pretty spot on.

I am not a surveyor (obviously)  

Thank you in advance!

Your drone data geotag Z vaules are in Height Above Ellispoid (HAE). You need to apply the Geoid height (Ellipsoid-Geoid separation), or whatever the difference is between the ellipsoid and your preferred vertical datum (if it is not orthometric) in Pix4D when you set the output coordinate system (under Advanced>Geoid Height Above the Ellipsoid).
You can get the Geoid Height for your study site from various online calculators (there is a UNAVCO one below). They will let you choose the Geoid model you wish to use (eg. GEOID 12B, GEOID 18, etc.). You may also be able to get the Geoid height for the CORS station which you could use if it is very nearby (the Geoid varies over space so if you want the best accuracy possible, use a Geoid height for the center of your study area. Unfortunately Pix4D only allows you to inpt a singe height. Some software will let you specify a raster file to better capture the Geoid height variability).



https://support.pix4d.com/hc/en- ... -Ellipsoid-Function

https://forum.dji.com/forum.php? ... =264115&pid=2733492

https://www.unavco.org/software/ ... ght-calculator.html

Can you check actual the RC battery voltage, in the Go app?

I agree with Patiam. In Agisoft Metashape you can put the geoid raster of your region, the software will automatically correct the altitude of the images. Otherwise you take out your raster in WGS84 EGM96 and you do the same manipulation in QGIS, it's free.

LV_Forestry Posted at 5-24 12:51
I agree with Patiam. In Agisoft Metashape you can put the geoid raster of your region, the software will automatically correct the altitude of the images. Otherwise you take out your raster in WGS84 EGM96 and you do the same manipulation in QGIS, it's free.

I've lost count of the number of posts on this forum with folks needing vertical coordinate systems explained...

patiam Posted at 6-4 07:42
I've lost count of the number of posts on this forum with folks needing vertical coordinate systems explained...

It's both simple and not easy to explain. If the interlocutor does not manage to orient himself well in space, it can quickly become long. The drawing you put in post #2 is perfect... If the person manages to admit that the earth is not perfectly round. If you have to deal with someone who believes the earth is flat, you're lost in advance.

You're right, it's a Sisyphean challenge. I think it's less a problem of folks being "flat earthers" than them just not having any concept about how vertical position is measured or reconciled, especially when GNSS works with a vertical datum that is so foreign to the layman. XY is much more intuitive for most people... Z not so much...

patiam Posted at 5-12 08:12
Your drone data geotag Z vaules are in Height Above Ellispoid (HAE). You need to apply the Geoid height (Ellipsoid-Geoid separation), or whatever the difference is between the ellipsoid and your preferred vertical datum (if it is not orthometric) in Pix4D when you set the output coordinate system (under Advanced>Geoid Height Above the Ellipsoid).
You can get the Geoid Height for your study site from various online calculators (there is a UNAVCO one below). They will let you choose the Geoid model you wish to use (eg. GEOID 12B, GEOID 18, etc.). You may also be able to get the Geoid height for the CORS station which you could use if it is very nearby (the Geoid varies over space so if you want the best accuracy possible, use a Geoid height for the center of your study area. Unfortunately Pix4D only allows you to inpt a singe height. Some software will let you specify a raster file to better capture the Geoid height variability).

Thanks for sharing, been using ODM -> QGIS, any suggestions on a workflow to get prover ELEV heights?

NAP3XD Posted at 9-3 13:55
Thanks for sharing, been using ODM -> QGIS, any suggestions on a workflow to get prover ELEV heights?

If you have the geoid in TIFF raster, in QGIS simply use raster calculator DSM-Geoid

LV_Forestry Posted at 9-4 05:17
If you have the geoid in TIFF raster, in QGIS simply use raster calculator DSM-Geoid

Thank for the response. I will check that out.

NAP3XD Posted at 9-4 17:14
Thank for the response. I will check that out.

Be sure that your geoid raster have the same coordinates system as your DEM before using the raster calculator