Hey, I'm using the drone for mapping and capturing images, and I checked in a 3rd party app that the altitude is not so correct.

Can I find in DJI Go app or flight record the altitude of the terrain? At least when it started fly?

Altitude will never precise.  Just in the ballpark

i like daftlogic.

https://www.daftlogic.com/projec ... ance-calculator.htm

Yeah, not so precise, but works.

In DJI GO, it shows the relative altitude, and the take-off point is 0.

The flight log contains the ultrasonic sensor height, only works up to around 10m but if you want to know the accurate height of each photo, you can take the photo, note the barometric height, then drop down until the ultrasonic sensors see the ground, subtract the new barometric height from the original and add on the ultrasonic sensor height.   That should give you a photo height above ground level accurate to maybe 1 meter without having to land.   If you have landing protection turned on then it is very quick to drop down to near ground level without hitting the ground.

Altitude information is saved in the Exif info that is part of each image you capture.
The mapping software uses this information and with photogrammetry correects altitude for the whole map you create.