Hello,
I am using the AHN3 5m dsm and dtm data for my thesis. I am trying to obtain the obstacle/ clutter heights (i.e DSM-DTM = obstacle height).
I was trying to find the height of the building at location 52.002301, 4.373623 ( Aula building at TU Delft). The DSM value obtained is -3.8039999 and DTM is -4.5539999 giving me an obstacle height of 0.75m, which is not possible.
The heights obtained is too small in a lot of such cases.
Any help will be appreciated!
Thanks
The DTM has NULL values where obstacles are, so subtracting is not possible.
I attached a profile image where you can see that the DSM value should be around 13-15 metres.
You could try filling in the gaps of the DTM. Then you’ve got a dataset that you can subtract from the DSM. There are several techniques to, each with their own pro’s and cons. I’ve had pretty good results with the interpolation tools of scipy.
Here is an example of an original surface model:
And here the same area after subtracting the filled in terrain model
Raw values are now the approximate height of the objects in relation to the surrounding ground level. The street level itself has a value of 0.
Thank you for the reply.
So the DTM values are supposed to be NULL where there are obstacles present (building, trees etc ), but due to some noise the values are not NULL , but should also not be considered ground heights. This makes it confusing to even use the DTM data, as you are never sure if the DTM value should refer to a NULL value, or noise or the actual height.
Is there a way to obtain clutter heights from DTM and DSM in any other way? I am new to this and some information about this would be helpful.
Thank you for the reply!
So if I understood correctly, you advice me to fill in the no data values with values from adjacent cell values heights using interpolation techniques.
But the DTM values also contain noise values in cells that are supposed to show NULL value due to the presence of objects. So how do you classify a cell to have a NULL value, or noise or the correct height data?
@Alkemade How did you obtain the heights in the profile image? Is that the value directly obtained from DSM data ? 
I didn’t really notice that in the past. But I was working with the AHN2 which due to the lower fidelity may have had less noise than the AHN3. Does the DTM near your point of interest look particularly noisy?
The profile can be made in the AHN viewer, compute a profile with the “AHN ruw” layer.
