Author: smathermather

My primary interest is in understanding ecological processes in a synoptic fashion. This has led me down a long study with Geographic Information Systems and Remote Sensing as they relate to ecology and biological processes.
Database, Database Optimization, PostGIS, SQL

Further optimization of the PostGIS LiDAR Vegetation Height Query

There’s much to be said for knowing your data in order to best optimize the analysis of it.  Beyond all other bits of cleverness, having a functional understanding of your problem is the first step toward conceiving an intelligent and efficient solution. One thing that I didn’t do two posts ago was to spend any time deciding how far out the search for nearby points … Continue reading Further optimization of the PostGIS LiDAR Vegetation Height Query

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Database, Database Optimization, PostGIS, SQL

Trigger Speeeeed, or triggers and data maintenance in PostGIS

I have completed 4 out of 6 of my triggers for maintaining boundary data in PostGIS.  This is a follow-up to this post.  If you haven’t read my PostGIS trigger post, follow this link and come back.  I’ll wait.  Go on. Back?  OK.  So I’ve implemented my property boundary triggers.  I need about 6-7 different versions of our boundary for cartographic reasons– some which are … Continue reading Trigger Speeeeed, or triggers and data maintenance in PostGIS

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Database, Database Optimization, PostGIS, SQL

PostGIS and LiDAR, the saga completes?

I have to thank this post for the code that follows http://postgis.refractions.net/pipermail/postgis-users/2009-June/023660.html: I’ve been putting at this nearest neighbor for points problem for a few months now, never dedicating enough time to think in through, nor expending enough energy to be really great at SQL, let alone how it can be applied in spatial operations with an OGC compliant database like PostGIS.  But here’s my … Continue reading PostGIS and LiDAR, the saga completes?

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Database, Database Optimization, PostGIS, SQL

Optimizing PostGIS Geometry Functions– Mmm. Donut.

Well, how can I PostGIS without referring back to BostonGIS.  One day I’ll know… .  But first, the Simpsons:  “Mmm… … Donut.” A while back I read Regina Obe’s BostonGIS post on “Map Dicing,” essentially using a grid to dice up an existing dataset to a small granularity in order to take full advantage of spatial indexing, etc..  The post really intrigued me, and is … Continue reading Optimizing PostGIS Geometry Functions– Mmm. Donut.

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Database, Database Optimization, PostGIS, SQL

Contour data and table management in PostGIS

My contour dataset is almost ready to go live.  Just a few more tweaks.  I was manipulating it in the public schema.  I really want it in my base map schema “base”. Want to change schemas on a table in Postgre? No problem: ALTER TABLE public.cuy_contours_2_clip SET SCHEMA base; Rename a table? No problem: ALTER TABLE base.cuy_contours_2_clip RENAME TO base.cuy_contours_2; Save space by not storing … Continue reading Contour data and table management in PostGIS

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Database, Database Optimization, PostGIS, SQL

PostGIS and LiDAR– oops!

I won’t offer much prelude.  Read this post, and this post first… . Inadvertently I demonstrated the value of spatial indices, i.e. I meant to use them and didn’t.  In attempting to sort my tables by their spatial index I got the following errors: ALTER TABLE lidar_ground CLUSTER ON lidar_ground_the_geom_idx; ERROR:  “lidar_ground_the_geom_idx” is not an index for table “lidar_ground” ALTER TABLE lidar_veg CLUSTER ON lidar_veg_the_geom_idx; … Continue reading PostGIS and LiDAR– oops!

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Database, Database Optimization, PostGIS, SQL

Rethinking PostGIS Analyses– Remembering to CLUSTER

Something’s been nagging at me as far as the level of optimization (or lack there-of) that I did to my database before my other posts of using PostGIS to analyze LiDAR data (e.g. this post).  It seemed my results were remarkably slow, but I couldn’t put my finger on why that was problematic. Then, as I was testing a smaller lidar dataset in order to … Continue reading Rethinking PostGIS Analyses– Remembering to CLUSTER

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Database, Database Optimization, PostGIS, SQL

PostGIS and LiDAR, the saga continues

I ran these tests a while back, but I’m just getting to post them now.  These were run on a late model MacBook Pro, with a 2.4GHz Intel Core 2 Duo, with a couple of gigs of RAM on PostgreSQL.  In Postgre, if I run SELECT version(); I get: PostgreSQL 8.4.1 on i386-apple-darwin10.0.0, compiled by GCC i686-apple-darwin10-gcc-4.0.1 (GCC) 4.0.1 (Apple Inc. build 5493), 64-bit My … Continue reading PostGIS and LiDAR, the saga continues

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GDAL

Mapping places unknown– free global datasets and FOSS GIS are a great combo

I wanted to put together a quick and dirty map of a biological reserve in Ecuador, sort of a laptop exploration of a place quite distant.  At first, I thought I’d use Shuttle Radar Topography Misssion data to get the elevation information.  Then I discovered the ASTER Global DEM which is 30m resolution for the whole world.  Wow.  Cool cool data. (I used the Japanese … Continue reading Mapping places unknown– free global datasets and FOSS GIS are a great combo

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