# Maximum height difference between drone & ground

Good morning,

I am planning to fly a mission at a coastal area, the majority of which has small height differences, but there are also some hilly parts.

My question is in a single flight, what is the maximum height difference between the drone and the ground. For example, if the drone flies 50 m above ground, the maximum ground height that can capture is 50 m, 30 m or less.

Hello,

I am not sure if I understand the question.

The flying height will determine the GSD (Ground Sample Distance) which gives the scale of the flight. If the GSD is 5 cm, it means that each pixel on your images will be 5 cm on the ground.

The maximum distance between the drone and the ground will depend on the GSD you want to get.

There is also a GSD calculator here.

If you fly a hilly area with a constant flying height, the GSD will differ from one place to another.

I hope my answer helps you.

Regards.

Let me ask you something else first. According to the article https://support.pix4d.com/hc/en-us/articles/202558979 , the highest GSD must be smaller than twice the lowest GSD.

This condition must be true only for the independent flights (independent projects) or for the final merged project ?

Hello,

That article refers to the difference in GSD size in order for the software to be able to find Key Points and it refers to both individual or merged projects.

When the difference is larger, as the pixel size is too different, the software cannot extract automatic points and could not connect images within the same block.

In addition, If you have two different projects with a large GSD difference and you want to merge them, the software will not be able to find Key Points and the merge would fail. However, if you are able to measure GCPs in common, the merge could be done.

Regards.