Should I use DTM or DSM to LAS?

[aringot]

Salut Nico 👋

Two related questions:

1. In Austria we do not get LAS but DTM (Digital Terrain Model) and DSM (Digital Surface Model) files. I saw I can convert these to LAS, but it is not clear to me which one I should use or if it is possible to combine these. Any advice?

2. I saw that OCAD can generate some features (e.g. contour lines) from DTM alone and can do more (e.g. vegetation height) if we provide DSM files in addition to the DTM. Do you actually use DTM/DSM in the background and could allow providing these directly like OCAD does?

Thanks for providing this open source! 🙌

[NicoRio42]

Salut Alexis, nice to hear from you 😃

DTM and DSM are not sufficient to generate a full orienteering map. You would theoretically be able to get everything but the vegetation densities out of it :

• From the DTM you could get the contours and the cliffs.
• From the DSM you could detect the forest parts (where the DSM height is way above the DTM height I guess).
  => But for the vegetation densities (green shades) you will need the full LiDAR point cloud. The algorithme computes the densities of points between 0.5 and 3 meters to get this information.

I do use DTM during the Cassini generation process, but no DSM. And as for now it is not possible to provide your own DTM to Cassini.

As DTM and DSM are usually computed from LiDAR point clouds (.laz or .las files), are you sure there is no way to get these raw data from the Autrian providers?

Don't hesitate to say hi if you're in Grenoble 😃