PostGIS users, I have 1:24k hydrographic linework that I need process in several successive steps using a postgis workflow.
I'm stuck at step 2 of this overall workflow: 1) separate all linestrings into distinct Strahler Order groups (done) 2) split all linework into linestrings of 500 ft (while avoiding any linestring fragments smaller than 500 ft) 3) perform an elevation lookup to raster data to calculate the gradient of each 500 ft segment and.. 4) combine all adjacent linestrings which fall into similar gradient classes. For step 2 I'm investigating using ST_Segmentize() and/or ST_Line_substring(), but I'd really appreciate some help with how to best approach the problem. ST_Segmentize seems to only insert more nodes/points into already very high resolution linework (ie nodes already exist at intervals much more frequent than 500ft), thus extracting linestrings from the result of ST_Segmentize clearly isn't as simple as using MakeLine() between each segment. ST_Line_Substring works on percentages which is smart, but I have yet to wrap my mind around how to measure each individual line such that I can translate percentage distance along a linestring into equal distance intervals. Anyone have examples or guidance? Thanks, Dane _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
