I am trying to determine mile markers along Texas highways. My starting point is the ShapeFile TxDOT Roadways 2010 at http://www.tnris.state.tx.us/datadownload/download.jsp. I've used shp2pgsql to get it into a PostGIS 1.52-enabled Postgres 9.01 database.
I naively thought I could just figure out the number of miles per unit of latitude and then traverse each roadway, one mile at a time, using * ST_Line_Interpolate_Point*. However, predictably, the more "longitudinal" a route, the more error it shows when I compare my calculated mile markers to what Google Maps shows. Again, this is because I was using a consistent ratio of degrees to miles, so any route E-W component introduces errors. So here's the question--does PostGIS allow any way to traverse a route a set distance at a time? Specifically, is there a way I can traverse a route a mile at a time and then record the points at the end of each mile? I reviewed the functions available at http://postgis.refractions.net/documentation/manual-1.5/reference.html and am not seeing anything clear. In case it matters, the SHP's PRJ file says NAD83. Aren Cambre
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