PostGIS interpolation / triangulation options

Question

I'm looking for an open source workflow to automate DEM construction. We have a series of sites that fall within a LIDAR dataset. We want to create site specific DEM's for each site, and we're looking to automate the process.

So far, we have automated:

• data loading into PostGIS (LIDAR and site points)
• creation of site boundaries (combination of st_buffer and st_envelope)

Now we're looking for options to interpolate the data subsets at each site and export them to Surfer7 grid files.

Currently, we're querying the data in the PostGIS database using QuantumGIS, exporting to csv files, then manually importing and gridding the data in Surfer7. Hopefully we can automate this as well.

So for this use case, we'd like to triangulate our lidar data to a DEM. Other potential cases we can think of involve different interpolation methods - so if there are options for inverse distance and kriging - we're interested!

This is very much a learning exercise for us - we're working in baby steps!

Answer 1

You could do this automation with SAGA, in Windows or in Linux. SAGA can handle big point data sets, imported in SAGA format as pointcloud format (spc). Then you have functions for interpolation or triangulation, and also export to Surfer. The automation is performed by using SAGA command tool.

Answer 2

If you have the original LIDAR data in .las/laz, you might use lastools, http://www.cs.unc.edu/~isenburg/lastools/ to deal with big LiDAR data. There's a las2tin and las2dem that look like they'd work directly, but I haven't used them. I have used the below to assemble a set of .laz files into a raster DEM within GRASS:

cat *.laz |~/Downloads/SRC/lastools/bin/las2txt -stdin  -parse xyztc -header pound -otxt |invproj -v -f %.9f +init=epsg:2284 |sed -e 's// /' | r.in.xyz input=- output=lidarJunk method=min type=FCELL x=1 y=2 z=3 fs=\    zscale=1.0 percent=100 --overwrite  
# the sed and fs=\ bits are for dealing with reformatting spaces and tabs between invproj and r.in.xyz

Lastools would automate well, and look like they could clip the data for a DEM or TIN to bounds of your choice.

Answer 3

Fusion/LDV - U.S.'s Forest Service free software for LiDAR processing and visualization. It comes with manual and tutorial with available ".las" data for training.

1- To set bounds on your data use the following program command:
ClipData (manual's page 35) or PolyClipData, if you have the shape files (manual's page 110);

2- To filter laser ground returns from your entire cloud use;
GroundFilter (page 88) If there is no vegetation; cellsize = 2 meters; otherwise, set cellsize. = 8 m. It will help to avoid labeling error (to assume as ground a non ground return).

3- To create DEM's use;
GridSurfaceCreate (page 82). It will assign for the pixel the average of z values ground returns which remained after previous step.

4- Convert DEMs to ASCII format;
DTM2ASCII (page 56)

hint: the software runs in DOS, so I suggest you to install a text editor (e.g. notepad++) to help you write the above (1,2,3 and 4 steps) program commands before running them (run each one at a time). If you'll use notepad++ save your file as ".bat" and whenever you are ready to go, press "F5" browse your ".bat" file and run it.