[postgis-users] Creating touching depth areas from gridded data

Hemant Bist hemantbist at gmail.com
Wed Feb 3 10:34:41 PST 2016

I have gridded data for ocean/lake(that gives depth of water at equidistant
intervals) and I am trying to extract polygon and multipolygons that
represent different water depth range.
example of gridded data set is  here
<http://www.gebco.net/data_and_products/gridded_bathymetry_data/> , and the
polygons  I am trying to create are ST_Multipolygon approximation of
different color areas in this image

I tried the simple approach of st_union grid rectangles with
st_snap_to_grid as mentioned here
The problem is that the resulting polygons have zig-zag edges. If I do
st_simplify or smoothening (grass v.generalize) I am left with polygons
that are not touching anymore (there is a gap between polygons that were
touching earlier).

Is there something in Postgis/Some other open source tool that I can use to
avoid this problem: get smooth polygons that touch each other. I will
appreciate any pointers.
There was some reference that "topology" may be able to help, but I am
unable to find a tutorial/example that would load the data in postgis and
extract smooth polygons.

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