Tag: Technical

GDAL

gdal_warp, cutlines, and cwhere– simple tip for use on Linux

Mini GDAL tip of the day: gdalwarp, especially in combination with gdal_merge, is a powerful tool for doing all sorts on nice aggregation (read: mosaic’ing) of spatial raster data.  Unfortunately, at least with a google search, there’s very little to be found on demonstrating the use of queries in conjunction with cutlines, probably because in general these queries are not difficult to figure out. In … Continue reading gdal_warp, cutlines, and cwhere– simple tip for use on Linux

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Analysis, Ecology, Landscape Position, Other, POV-Ray

Landscape Position: Conclusion? (part 2)

From earlier post: “I’ve managed to pilot most of a fast high resolution landscape position workflow with PovRay as my magic tool. The final steps I hope to pipe through PostGIS Raster. In the meantime a screenshot and description: blues are riparian, raw ocre, etc upland categories, grey is mostly flat lake plain and mid slopes, all derived from just a high res DEM input … Continue reading Landscape Position: Conclusion? (part 2)

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Database, GeoServer

Leaflet, GeoServer, and Open Source Software Ramblings

I posted this post about an apparent problem in rendering of GeoJSON in Leaflet, and now it’s fixed a week later.  Why gush now, when for a few years developers on the GeoServer board have been fixing bugs I’ve found (often by the next day)?  Well for one, I very rarely find bugs in GeoServer– I just think I do, document everything, send it on, … Continue reading Leaflet, GeoServer, and Open Source Software Ramblings

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Analysis, GDAL, Image Processing

gdal_calc.py– Raster Calculator using Numby Functions

gdal_calc is a python script that makes it easy to do band math and logical operations with gdal/numby. This ranges from basic arithemtic operations to logical functions. And while gdal_calc.py has been around since 2008, it is but is a recent and revelatory discovery for me. I had just today resigned myself to properly learning python so as to use the gdal bindings. But, my … Continue reading gdal_calc.py– Raster Calculator using Numby Functions

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Analysis, Ecology, Landscape Position, Other, POV-Ray

Landscape Position: Conclusion?

I’ve managed to pilot most of a fast high resolution landscape position workflow with PovRay as my magic tool. The final steps I hope to pipe through PostGIS Raster. In the meantime a screenshot and description: blues are riparian, raw ocre, etc upland categories, grey is mostly flat lake plain and mid slopes, all derived from just a high res DEM input (no hydro lines … Continue reading Landscape Position: Conclusion?

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GeoServer

Complex Symbolization in GeoServer or Compass Rose Mania– the GeoServer Version

At my place of employment, we have a vegetation survey program with enough potential plots to serve 50 years of data collection. The points are laid out in a Generalized Random Tessellation Stratified (GRTS) to maximize the statistical power of the analyses we do with them. Read more about GRTS. I dare you. Actually, it’s not so bad if you understand Quad-Trees and the like– … Continue reading Complex Symbolization in GeoServer or Compass Rose Mania– the GeoServer Version

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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, SQL

PostGIS 2.0SVN and Raster

Got PostGIS 2.0 installed on a Debian machine, with Raster enabled, and put my first image in thanks to the directions in PostGIS In Action. Here’s the auto-generated SQL in pgAdmin: CREATE TABLE ldi_10ft ( rid serial NOT NULL, rast raster, CONSTRAINT ldi_10ft_pkey PRIMARY KEY ( rid ), CONSTRAINT enforce_srid_rast CHECK (st_srid( rast ) = 3734) ) WITH ( OIDS=FALSE ); CREATE INDEX ldi_10ft_rast_gis_idx ON … Continue reading PostGIS 2.0SVN and Raster

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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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Analysis, GeoServer, PostGIS

What is the center line of a complex polygon? (cont. 3)

Just a quick post on this one, this time. I haven’t implemented an approximation of Bálint Miklós‘ Scale Axis Transform in PostGIS yet, and I don’t think I’ll dare try in GeoTools for GeoServer just yet, but I thought I’d give a preview of the sensitivity of the medial axis calculations in “bumpy” streams with the following image: As you can see, the problem isn’t … Continue reading What is the center line of a complex polygon? (cont. 3)

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