The Problem We have to filter out the roads and ditches without removing streams that cross roads or follow them closely. I’m going to use PostGIS to find the intersection of the streams lines data with a buffered roads polygon. If the intersected line is less than 50% of the length of the stream line, […] via Filtering Roads from Extracted Streams Data — GeoKota Continue reading Using PostGIS for Hydrologic Modeling (reblog)
A little more refinement to the SQL for building masking fill for hand-placed text on maps. Continue reading Cartographic tricks and tips– making text readable, PostGIS edition, take 3
I have a couple of posts number 1 and number 2 about masking for text. One more from the actual implementation: Continue reading Cartographic tricks and tips– making text readable, PostGIS edition part 2
Recall from previous post, http://wp.me/phWh4-qm I played a bit with using convex polygons and buffers to control noisy backgrounds behind text, ala: ——–> I was tired of doing this in the GUI in QGIS, so I wrote some simple code to do it in PostGIS. Continue reading Cartographic tricks and tips– making text readable, PostGIS edition
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)
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
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
For one of our applications, we need 8-point compass roses placed at each of our points, as well as a circle 40 meters in diameter as well as one 140 meters in diameter. We did a bit of work with this a while back in GeoServer using SLDs. Now we’d like to refine it, and implementing this in an SLD is beyond my skills. So, … Continue reading PostGIS for Dessert: Sketching shapes in #PostGIS– compass roses revisited
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