DTM Tutorial

[HMArnold]

I'm trying to learn how to export a DTM from aerial images

There is a forum post that references a tutorial, but the link goes to the main Photoscan page.

Is there such a tutorial?

Thanks

Hank

[stihl]

DEM/DTM without GCP's: http://www.agisoft.com/pdf/PS_1.2%20-Tutorial%20(BL)%20-%20Orthophoto,%20DEM%20(without%20GCPs).pdf

DEM/DTM with GCP's: http://www.agisoft.com/pdf/PS_1.2%20-Tutorial%20(BL)%20-%20Orthophoto,%20DEM%20(with%20GCPs).pdf

[HMArnold]

Thanks, but the term "DTM" never occurs in those files

Its probably my understanding of the file type

If someone is looking for a DTM, and expecting a file with an "ASC" extension, is a "DEM EXPORT TIFF/BIL/XYZ", then an "Arc/Info ASCII Grid (*.asc)" what I'm looking for?

[stihl]

DEM stands for Digital Elevation Model

DTM stands for Digital Terrain Model

The clear difference between the two is that a DEM is generated by connecting all the points in the Dense Point Cloud, whilst a DTM is generated by connecting only the ground points that are in the Dense Point Cloud by using an IDW (Inverse distance weighted) interpolation technique.
A DEM is made out of all the elevation points and a DTM consists of only the terrain points, hence their names.

Creating a DEM is done by generating a Dense Point Cloud and afterwards running the Build DEM option with default settings. Once a DEM is made you can export by going to File > Export DEM > Export TIFF/BIL/XYZ.
In this window you can set the desired resolution of the DEM and export it to an Elevation GeoTIFF (or ESRI ASCII if you prefer) file.

Creating a DTM is done by determining the ground points from non ground points (e.g. buildings/vegetation/cars/street poles). This is done by running the classify ground points option after you've generated a Dense Point Cloud.
Once this is completed you need to use the Build DEM option to generate a surface model, only you need to specify which points to interpolate.
In the Build DEM window you'll need to set the Select Point Classes set only to Ground. After this is completed you can export it the same way only you've ended up with a DTM instead of a DEM.

[HMArnold]

PHEWEE!

I wasn't even close

Thanks very much for your help

I'll study and try that