DEM consistently approx 18 meters lower than it should be

[jargo]

Hi there

Excuse my not so scientific lingo, working with DEM's is rather new to me.

I have just completed my DEM of a 100 hectare coastal area. For the DEM I followed this guide:
 https://agisoft.freshdesk.com/support/solutions/articles/31000153696-aerial-data-processing-with-gcps-orthomosaic-dem-generation

However I was a bit unsure, so when correcting the GCP's in "Add markers" step 5, I manually adjusted ALL pictures with the GCP's in them. I'm not sure this is right.

After the creation of the DEM I noticed that the area was consistently about 18 meters too low, making all the area below sea level. Is there a way to fix this? Should I start over, and if so, how do I correct the mistake that made then wrong DEM?

Even though the DEM was wrong compared to the real world, the internal accuracy seemed fine, as I am able to do hydrological modelling in another software. Not all is doable though, since the terrain is 18 meters below sea level and right next to the ocean...

Regards, Jacob

[dpitman]

Hello Jacob,

That tutorial is missing a key step when it comes to non-rtk drone image sets.  Before optimization, you need to uncheck the cameras so that precision will be applied from the GCPs. 

ser SAV posted a nice concise summary of steps here:
https://www.agisoft.com/forum/index.php?topic=7851.0


Dave