Category: Analysis

Analysis, Database, PostGIS, PostgreSQL, SQL

What is the center line of a complex polygon? Routing Stream and Rivers

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

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Analysis, ArcGIS, Database, PostGIS, PostgreSQL, SQL

Proper (ab)use of a database, contour interpolation using #postgresql #postgis #arcgis

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

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Analysis, Database, PostGIS, PostgreSQL, SQL

What is the center line of a complex polygon? Routing as the solution

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

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Analysis, Database, Database Optimization, PostGIS, PostgreSQL, SQL

Cartography and USGS — Fake Building Footprints in PostGIS now with distance operator (part 2)

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)

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Analysis, Cartography, Database, PostGIS, PostgreSQL, SQL, Trail Curation, Trails

Going deeper into web cartography: future=past? (and Swiss cartographic genius)

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)

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Analysis, Cartography, Database, PostGIS, PostgreSQL, SQL

Cartography and USGS — Fake Building Footprints in PostGIS now with distance operator

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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Analysis, Cartography, Database, PostGIS, PostgreSQL, SQL

Cartography and USGS — Fake Building Footprints in PostGIS now with distance operator

Quick and fun post tonight.  Remember in USGS quads all the little building footprints that represented civilization?  We (me and my colleague John Stein) were contemplating how to pull off something similar with address points.  Here was our first attempt: It looks ok, but may be a little crude to be considered cartography (click on it to see it bigger– you’ll see those buildings don’t … Continue reading Cartography and USGS — Fake Building Footprints in PostGIS now with distance operator

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Analysis, Optics, Other, POV-Ray

Fast Calculation of Voronoi Polygons in PovRay

Yet further abuse to follow in the application of PovRay for spatial analyses– be forwarned… . Calculating Voronoi polygons is a useful tool for calculating the initial approximation of a medial axis. We densify the vertices on the polygon for which we want a medial axis, and then calculate Voronoi polygons on said vertices. I’ll confess– I’ve been using ArcGIS for this step. There. I … Continue reading Fast Calculation of Voronoi Polygons in PovRay

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