Dear Grass Users, I am having trouble with interpolating a canopy height model using v.surf.rst and some lidar data. The lidar point density ranges from 5 - 8 points per meter squared. I know I can import the data using r.in.xyz but I would prefer to use an interpolation technique as opposed to a spatial average. I chose r.surf.xyz based on the paper written by Helena Mitasova, Lubos Mitas, and Russell S. Harmon. While the applications differ the use of a large data set with many points means dealing with the same issues. I ran the algorithm using default values and the result was a smooth moon-like surface not really approximating a plantation forest canopy (see link 2)
v.surf.rst input=areaone_4...@wesley layer=1 zcolumn=dbl_3 elev=Area1_4_def tension=40. segmax=40 npmin=300 dmin=0.050000 dmax=0.250000 zmult=1.0 Given that I am working with very dense data with a high number of points I then ran the algorithm with a smaller tension value (roughly 2.5) with an incrase in the maximum number of points per segment (decrese computation time) and I find that the interpolation is blocky in nature. (see link 3) v.surf.rst input=areaone_4...@wesley layer=1 zcolumn=dbl_3 elev=Area1_4_def6 tension=2.5 smooth=0.0001 segmax=100 npmin=300 dmin=0.050000 dmax=0.250000 zmult=1.0 Is the blockiness related to the increase in the maximum number of points in a segment i.e. segmax value? I have also been looking at using R to do the interpolation using gstat or automap. Does anyone on the list have any advice with regards to methods to use for the interpolation of lidar canopy returns, with a view to creating a 3-D model of the canopy. The website spatial-analyst (http://spatial-analyst.net) suggests the use of regression-kriging but I don't have any ancillary data besides height and intensity. I have uploaded pics of the study area and interpolation results to flickr (everyone should have access to these) Link 1 http://www.flickr.com/photos/35273...@n07/3271646498/ Link 2 http://www.flickr.com/photos/35273...@n07/3270854029/ Link 3 http://www.flickr.com/photos/35273...@n07/3270904761/ Many thanks for taking the time to read my post and for your valuable contributions Wesley (I am using Grass 6.3.0 on Ubuntu Hardy Heron) Wesley Roberts MSc. Researcher: Earth Observation (Ecosystems) Natural Resources and the Environment CSIR Tel: +27 (21) 888-2490 Fax: +27 (21) 888-2693 "To know the road ahead, ask those coming back." - Chinese proverb -- This message is subject to the CSIR's copyright terms and conditions, e-mail legal notice, and implemented Open Document Format (ODF) standard. The full disclaimer details can be found at http://www.csir.co.za/disclaimer.html. This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. MailScanner thanks Transtec Computers for their support. _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
