Change Altitude after download?

[LI Surveydrone]

I've been working with the Phantom 4 pro for several months and it's been great. The first model of a specific site worked out very well. A week later, I did a second flight. When I downloaded the photo's, the altitude reading was negative. When I created the model, the surface ended up being 200' below my GCP's.
Any suggestions?
Can I change the altitude of my photo's before processing them?
Thank you for your help

 

[Meta4]

I've been working with the Phantom 4 pro for several months and it's been great. The first model of a specific site worked out very well. A week later, I did a second flight. When I downloaded the photo's, the altitude reading was negative. When I created the model, the surface ended up being 200' below my GCP's.
Any suggestions?
Can I change the altitude of my photo's before processing them?

It's very common for the altitude data in the images to be inaccurate as it comes from GPS which is very unreliable for altitudes as this example shows:

I wouldn't think that changing the altitudes would be the way to go.
The idea is for the GCPs data to do the correcting.
After you add the GCP data, is your surface in the right place?

 

[LI Surveydrone]

It's very common for the altitude data in the images to be inaccurate as it comes from GPS which is very unreliable for altitudes as this example shows:
5-7'

I wouldn't think that changing the altitudes would be the way to go.
The idea is for the GCPs data to do the correcting.
After you add the GCP data, is your surface in the right place?

Thanks for getting back to me about this problem.
After I enter my GCP's, they're pretty close to the elevations of the cameras.
After conversion, the camera elevations averaged around EL:20 while the GCP's averaged EL:5-7'.
The surface was created around EL:-200'. The height of flight was set around 235' AGL.