I will build a GIS system based on polygons, not just points.
I wanted to use mongodb or postgis.
how do this in mongodb?
Query A – get the center of a polygon
Query B – distance between two polygons
Query C – list of polygons that are part of a third that I specify
Query D – near distance of the polygon
support SRID?
Best Answer
Currently MongoDB does not support these spatial operations - only Geospatial Indexing of 2d points is supported with some basic accompanying queries (near, within). If you need them you would need to develop support from scratch. Hopefully in the future this will be included.
However if you are interested in storing spatial data in a NoSQL database (instead of a standard relational database, such as PostGIS) you could try CouchDB with the geocouch extension. Geocouch uses GeoJSON to store geometry so polygons can be stored. However as far as I can see only boundnig box queries are supported so far - which you could use to narrow your search - with hopefully polygon and radius search, and srs support coming soon. (Also, a tutorial that I found from Todd Jackson gives a good run-through on getting started. And see this question on GIS SE.).