Thursday, January 30, 2014

LiDAR Surface Models Graphic

I don't think this has enough cartoons to qualify as an infographic, but I hope it helps to illustrate the workflow used to create some common LiDAR raster surface model products from a point cloud.

Digital Elevation Model (DEM) - ground surface topography
Digital Surface Model (DEM) - elevation of all features including the ground, building, trees, etc.
Normalized Digital Surface Model (nDSM) - height of features relative to the ground.


Martin Isenburg said...

Subtracting rasters is one way to create an nDSM (or CHM). We prefer to normalize the points and then directly interpolate the normalized LiDAR points. This allows us to create pit-free nDSMs (or CHMs) that are especially useful for better post processing in forestry applications. See RIEGL's feature for links to poster and abstract (with LAStools script).

Jarlath O'Neil-Dunne said...

Thanks for the post Martin. We have done it the other way around. first produced the nDSM, then fused it with imagery to extract tree canopy. Once we have the tree canopy then we filled in the holes in the nDSM for the tree canopy areas only to create a CHM. The approach works well in heterogeneous environments where you don't want to fill in areas such as utility lines and buildings, but the cognitive processing is heavy on the RAM, which is why my last workstation cost me $22,000!

Martin Isenburg said...

Interesting. Had not thought about heterogeneous environments before. Wonder how to create such a workflow with points. Maybe filter out powerlines, then lascolor.exe the LiDAR points to color filter those that correspond to the canopy. Then create the set of partial CHMs (that are stacked on top of the standard CHM to generate the pit-free CHM) only from those points identified as being in the canopy?

dnewcomb said...

From the standpoint of a bird, how much difference does a perch from a power line or roof make to perch in a tree branch? Just because the structures are not trees does not mean they are not used. I would not be so quick to ditch the non-tree points.

Jarlath O'Neil-Dunne said...

In our case we don't ditch non-tree points, but knowing what is a tree and not a tree is very important both in terms of wildlife and urban heat island.