A while back, I had the idea of creating a hash of geometry in order to create a unique constraint on geometry to avoid duplicate geometries in a PostGIS table. It works. It’s slow, but it works. I haven’t used it since. What I really wanted to do though was be able to detect if geometries were similar as well (not just detect identical geometries), … Continue reading PostgreSQL and Fuzzy Hashes– a natural combo?
In an earlier post, I was frustrated with the intersection of a polygon and line datasets coming out as a geometry collection instead of a simple line dataset as expected. Nicklas Avén was kind enough to point out that this is a natural consequence of the logic of an intersection, the definition of ST_Intersects is: Returns TRUE if the Geometries/Geography “spatially intersect” – (share any … Continue reading The PostGIS learning Curve: ST_Within and ST_Crosses
One thing I’ve learned in the last few years is that there is no theoretical reason why (properly indexed and summarized) data cannot be displayed at all scales as quickly as at any scale. This is the principle at work behind the extraordinary efficiencies of delivering data and imagery through a slippy map interface like Google, Bing, and OpenLayers as well as efficient thick client … Continue reading GeoServer and efficient delivery of raster data (image pyramid layer)
This will be a very quick post today. We wanted to use some historical USGS quads for analysis. We had a ready source, used ArcGIS to georeference them to a grid, but then wanted something approaching a seamless product. Enter gdal. First step, create an image to put the mosaic into: gdal_merge -o usgs_merge.tif -createonly input1.tif input2.tif … Then mosaic into that. Since we have … Continue reading Historical USGS Quads
The disk that held the personal geodatabases of our contour datasets died a while back, but not before I loaded the contours into PostGIS and started serving them up. Our new intern is working on putting together some shapefiles layer groups in ArcGIS for map production, and asked for a missing one… . I don’t have it, but in principle can always extract it from … Continue reading Geometry Collections and Small Headaches
As we move away from a simple stack of PostGIS/GeoServer/GeoWebCache/Openlayers to wrapping a MapFish print service into the stack, it’s time to think more seriously about optimizing and stabilizing GeoServer. In preparation for this step, I’ve been setting up a series of VMWare ESX-hosted Debian Linux VMs to function as the cluster of geospatial services. Fortunately for me, there’s plenty of great advice in Andre … Continue reading GeoServer Optimization
I promised pics from our labeled parcels: https://smathermather.wordpress.com/2011/02/01/parcel-annotations-in-geoserver-with-some-maplex-help/ https://smathermather.wordpress.com/2011/02/01/parcel-annotations-in-geoserver-with-some-maplex-help-cont-1/ Continue reading Parcel Annotations in GeoServer (with some Maplex help) (cont. 2)
smathermather: We have a guest blogger today– Ramon, a bright and hard-working intern I’ve had the pleasure of working with for over a year. If you’re looking for someone versed in Postgre/PostGIS/GeoServer/OpenLayers, Ramon’s been my rock as we’ve been building our internal system, doing everything from basic grunt work to esoteric trouble-shooting. I’m trying hard not to fall on my face now that he’s moved … Continue reading Parcel Annotations in GeoServer (with some Maplex help)
I typed that last one too quickly– too many typos, but my wife says I’m not supposed to revise blogs, but move on… . So, for clarity, let’s talk a little more about McNab indices. Field-derived McNab indices are a measure of average angle from the observer to the horizon (mesoscale landform index), or from the observer to another field person a set distance away, … Continue reading Landscape Position and McNab Indices (cont.)
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