# Vertical Accuracy in Topographic / DEM Mapping /. 3D

I’m wondering if anyone has determined what the approximate average vertical accuracy is for a DEM / Topographic Map.  I realize it would vary based on a lot of factors like:

1. Photo resolution and overlap

2. If and how many, and at what angle oblique photos were taken

3. Relative accuracy of the drone’s altitude measurement

4. Other?

Let’s take a “typical” situation, using a DJI Phantom 4 drone 70% sidelap/overlap, 5cm/pixel GSD, one set of nadir photos and then obliques at same overlap at 45 degree angle.

Anyone have even a clue if the vertical measurements on the dem would be say within 15cm.  I other words if point is identified as being 150cm off the ground, actual elevation of the point is +/- 15cm or between 135-165cm off the ground.

I’d recommend this article about accuracy from the knowledge base. A rule of thumb is that the accuracy of a point in Z is between 1 and 3 times the average Ground Sampling Distance (GSD) of the project. In your case ± 15cm seems alright.