Category: PostgreSQL

Analysis, Database, PostGIS, PostgreSQL, SQL

What is the center line of a complex polygon? (cont. again!)

I didn’t remember that I had 4 previous post on this topic, but I’ve gotten a little obsessed with this problem– how to (with relatively little computational cost) kind the centerline of complex polygons, so we can extract flow lines from streams, label long complex polygons, easily generate the centerline parcel boundary line for river bound parcels, etc..  FYI, here are my 4 previous posts … Continue reading What is the center line of a complex polygon? (cont. again!)

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

PostGIS Cartographic Effects– Cartoonify Nearly Coincident Lines

In my previous post, a long 24-hours ago, I proposed some automatic modification of line for cartographic reasons. I had some flaws in my code. The points were over-rotated by 45 degrees. Can you spot why? Tip: it’s a basic trigonometric mistake. Here’s the corrected code (though there may be a better way): An alternate approach is to only move those points that are too … Continue reading PostGIS Cartographic Effects– Cartoonify Nearly Coincident Lines

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

PostGIS Cartographic Effects– Cartoonify Nearly Coincident Lines

I’m still working on this query, but I thought I’d post what I’ve done so far. My intent is to produce scale-dependent exaggeration of the distances between quasi-parallel lines. The reason for this is so that lines such as street lines which are nearly coincident at a particular viewing scale can be spread from each other, much in the same way great cartography lies a … Continue reading PostGIS Cartographic Effects– Cartoonify Nearly Coincident Lines

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CartoDB, Database, Leaflet, PostGIS, PostgreSQL, SQL

CartoDB, Leaflet, and a little anti-generalization

CartoDB is one of two hosted (read: cloud) PostGIS database implementations.  It has a maps API, an SQL API, and is some fun to use.  The other hosted PostGIS implementation is SpacialDB which has a Restful API, but can also take SQL.  I just got my key for the free version of that, so hopefully I will be reviewing use of that in the future … Continue reading CartoDB, Leaflet, and a little anti-generalization

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Database, PostGIS, PostgreSQL

PostgreSQL dump for PostGIS upgrade

I’m working through the Hard Upgrade instructions for PostGIS 2.0SVN install instructions. No great surprises, but a succinct set of steps for trying out PostGIS 2.0 early. In our case, we needed to exclude larger (30GB) tables from the dump needed to do an upgrade– we’ll build those into the new database selectively. Looking to the pg_dump instructions, the dash “T” (-T) flag is what … Continue reading PostgreSQL dump for PostGIS upgrade

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