DTM vs DEM – what does it mean?
If topography is the reason for aerial survey, vegetation and buildings can insert false readings into the data. Using Agisoft Metashape it is possible to classify and filter out the unwanted data.
The following video shows some of the stages involved to remove the trees from this particular dataset.
Stages of PhotogrammetryA short video showing some of the stages in photogrammetry processing.1) Sparse Cloud2) Dense Cloud showing point confidence3) Dense Cloud showing point classification4) Textured colour model5) Point classification Dense Cloud with trees turned off6) Textured mode lwith trees removedCreated by 3dmb.uk
The stages shown are:
- Sparse Cloud – the first completed process created during image alignment
- Wireframe Mesh showing the lumps created by the trees
- A dense cloud coloured to show point confidence
- A dense cloud showing point classification – the trees are shown in white
- A coloured mesh showing the quarry with trees
- A dense cloud with trees removed
- A coloured mesh showing the quarry with trees removed
This process can be used to create DTM (digital terrain model) as opposed to a DEM (digital elevation model). DTMs display the ground topography. The following images show DTM & DEM of the same area.