Just discovered ST_Node, a function in PostGIS just for noding geometries. I used to use ST_Union for this, a potentially memory intensive operation. Now I can use ST_Node. For usage, see the PostGIS docs (requires 2.0 and GEOS 3.3.2 for bug free use). Back to coding. That is all. Continue reading Using ST_Node in PostGIS (where once I used ST_Union)
Sadly, I cannot post the code for this one, but will post the images– playing with tesselation in PostGIS today: Continue reading Tesselation of Hexagons in PostGIS
The series and one additional example: Continue reading What is the center line of a complex polygon? Routing Stream and Rivers Part Two
Continuing my posts on the centerline of a complex polygon (you can work your way backward from here), here’s it’s application to a riverine system (legend: light blue river, black centerline derived from routing through the skeleton of voronoi polygons from a densified stream bank set + the skipped skeleton bits in pink– read through the series if you if you don’t grok that explaination): Continue reading What is the center line of a complex polygon? Routing Stream and Rivers
Anyone who has been following along at home knows I don’t think much like a DBA. Sometimes that’s good; mostly it’s probably bad. In this post, I hope it will be interesting. The problem of the day is how to take engineering contours derived from breaklines, a lidar point cloud, and all the lot, and do a good job interpolating that to a DEM. This … Continue reading Proper (ab)use of a database, contour interpolation using #postgresql #postgis #arcgis
I’ve had a series of posts (including this one) on finding the center line of a complex polygon– especially with an interest in finding the center line of streams and river bodies. We have to give credit to my colleague Tom Kraft for solving the polygon centerline problem. Tom struck upon the very elegant solution– derive the medial axis, and then use a few end … Continue reading What is the center line of a complex polygon? Routing as the solution
Just pretty pictures today. Continue reading Cartographically Pleasing Vegetation Boundaries– with PovRay, PostGIS, and LiDAR
In a previous couple of posts (this one, and this one), we dealt with point rotations, first with bounding box searches, and then with nominal use of operators. First we create a function to do our angle calculations, then use select to loop through all the records and do the calculations. Within our function, first we find our first (in this case) five nearest streets … Continue reading Cartography and USGS — Fake Building Footprints in PostGIS now with distance operator (part 2)
My favorite cartography book is Eduard Imhof’s Cartographic Relief Presentation. A few years back I picked this book up (translated to English) from ESRI press for $75 if memory serves me. Now it can be gotten for much cheaper. Imhof spends a lot of time on feature simplification and separation, a problem which keeps me up at night. For example, if you have a lot … Continue reading Going deeper into web cartography: future=past? (and Swiss cartographic genius)
In a previous post (I feel like I say that a lot), I wrote about rotating address points to match nearby roads in replicate the effect of USGS quads that represented small buildings with little squares that followed the nearby road alignment. The function was effective: but deadly slow when applied to all 500,000 address points. And so we iterate. First, I’ll show you our … Continue reading Cartography and USGS — Fake Building Footprints in PostGIS now with distance operator
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