Now that I have a RELAX NG Compact schema of GPX, it’s time to figure out how to get my data in to PostGIS. so I can do geospatial queries. I installed PostGIS on my Ubuntu box with these instructions. If I recall correctly, the latest version didn’t work but the previous release did.
GPX makes a great GPS data interchange format, particularly because you can convert just about anything to GPX with GPSBabel. I’m not aware of anything that can convert straight from GPX to PostGIS, but it is a relatively straightforward two-part process.
The first order of business is converting our GPX file to an ESRI Shapefile. This is easiest done by using gpx2shp, a utility written in C that is also available in Ubuntu. Once gpx2shp is installed, run it on your GPX file:
Once we have a shape file, we can use a utility included with PostGIS to import the shapefile in to postgres. The program is called
shp2pgsql, and can be used as such:
shp2pgsql -a shapefile.shp tablename. I tend to prefer the
-a option which appends data to the table (as long as it’s the same basic type of the existing data). shp2pgsql generates SQL that you can then pipe in to psql as such:
shp2pgsql -a shapefile.shp tablename | psql databasename.
Once the data is in Postgres (don’t forget to spatially-enable your database, you can query it in ways that I’m still figuring out. A basic query like this will return a list of lat/lon pairs that corresponds to my GPS track:
select asText(the_geom) from tablename;. I’m llooking forward to wrapping my head around enough jargon to do bounding box selects, finding things nearby a specific point, etc.
The examples in the PostGIS documentation seem pretty good, I just haven’t figured out how to apply it to the data I have. I feel like mastering GIS jargon is one of the biggest hurdles to understanding PostGIS better. Well, that and a masters degree in GIS wouldn’t hurt.