Category: SQL

Code Sprint, Conferences, Database, PostGIS, PostgreSQL, SQL

Boston Code Sprint

I hung out this week at the Boston Code Sprint http://wiki.osgeo.org/wiki/Boston_Code_Sprint_2013, which is a “C-Tribe” code sprint for improving things like PostGIS, MapServer, and other GeoFOSS projects written in C. See Paul Ramsey’s posts on PostGIS and MapServer for more on what everyone was working on. Being my first time at a code sprint, it’s been very interesting, and it’s a very warm and inviting … Continue reading Boston Code Sprint

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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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