Terrain model out of DSM

[George]

Hello guys,
did any one tried and succeded in creating DTM from DSM (DEM generated from Pscan)?
What were your ingridients?
George

[Kjellis85]

Can you specify a bit what you mean by terrain model? A Digital Terrain Model or Digital Elevation Model is exactly just that, a model of the terrain. All you need is a georeferenced model in photoscan and to export that as a DEM in your desired coordinate system.

[frank.stremke]

hi,
if i understand your question correctly then the answere is a clear maybe.
it can be done depending on the kind of vegetation and building infrasrtucture. you will have to create and export an dense point cloud as lidar data and then edit it for example with lidartools or even open source gis software (Grass)
frank

[photogrammetrix]

Hi

there are some moving-window filter for slope-based filtering of raster-dsm. Vosselman et. al have done great work on this for lidar data. In case of flat terrain this works quite well also for photogrammetrically derived point clouds and you can get rid of most surface objects. But there is one big problem: forested areas. when there are not enough 3D points on the ground, there DTM reconstruction will be very poor or at least totally wrong and cannot compete with lidar. Other options will be to directly concentrate on the point cloud itself. May you want to take a look at PCL (Point cloud library) There are some nice filters, but I am running into performance problems when dealing with massive pointclouds of several Mio of points, which are common when doing terrain reconstruction

Please report when you have found a nice way.

Cheers

[George]

Hi guys,
thanks all for the input.
Sure under DTM I mean bare earth i.e. just ground.
Yeah! Forest is the problem and actually this is a huge challenge to find points in a dense PC which are exactly on the ground level.
LAStools have a nice module, which thins lowest or highest points with a certain grid but this is not enough because PC itself is sometimes quite noisy, which means those lowest points may be absolutely wrong.
What about point cloud engines to process PC manually?
Regards, George