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There is an easier and more efficient way of doing this. Works for both PostGIS 2.1 and 2.0. Just use the ST_ValueCount function. http://postgis.net/docs/manual-2.1/RT_ST_ValueCount.html that will give you both the pixel value and number of pixels that have that value. So would be for your case SELECT DISTINCT (pvc).value FROM (SELECT ...
There are various forms of ST_Value and the one that will probably help you is the ST_Value(rast, band, x, y) one. Modifying one of the examples from the docs, you can dump all the values for each pixel using generate_series in the x and y direction, and then use group by (or distinct) on those to get the list of unique pixel values. SELECT count(b1val), ...
Let me respectfully disagree, but I don't think that the Hausdorff distance function is the appropriate way to snap a GPX track to a street network. Rather you should be looking into methods for map matching, e.g. Different approaches for map matching : links / ideas?
I guess you added in your classpath gt-epsg-postgres instead of gt-epsg-hsql? Delete gt-epsg-postgresql-11.0.jar from your classpath and add gt-epsg-hsql-11.0.jar into it. EDIT(Inspired by comments): For making the answer more understandable for others: GeoTools was set to store the EPSG projection database into PostgreSQL database. The default is to use a ...
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