[postgis-users] Can we store physical locations using local coordinate system in postGIS?

[Paul Ramsey]

PostGIS does its conversions using PROJ4, and only transforms that can
be expressed in PROJ4 are magically supported. To convert between
local system (between a local UTM and Lambert, for example) the
coordinates actually go first from UTM to geographics, then from
geographics to Lambert. The upshot being, that the only way to do
local transforms using in-built PostGIS functionality is via
geographics, so your transforms from local to geographic have to exist
from the start, not "eventually".

Now, you could invent your own system, using a side table to store
affine transform matrix information and the ST_Affine function to
convert between local systems. And then a final set of Affine
relations to convert to a local UTM grid, which then gets you out to
geographics in the end. But that'll be your work, not something you'll
get form in-built functionality (except for the affines, those are
there)

Yours,

Paul

On Fri, Aug 16, 2013 at 2:09 AM, Harshal Vora <harshal at amideeptech.com> wrote:
> Hi,
>
> I am new to PostGIS. I have been going through the documents. I have until
> now understood that we can provide coordinates for any physical location but
> the coordinates should make sense in one of the coordinate systems available
> in the SRID table.
>
> We are working on a product where we would like to store floor plans of
> buildings into PostGIS. We want to use our own coordinate system (in feet or
> meters). Also we want to store a hierarchy of physical locations i.e.
> building contains floors, floors contains rooms etc. We want to provide
> local coordinate systems to each level in the hierarchy and also provide
> capability to convert from one coordinate system to another as we move up
> and down the hierarchy.
>
> Is it possible in PostGIS to store hierarchical relations? Is it possible to
> use local coordinate systems and provide info on how to convert from one
> coordinate system to another?
>
> Eventually we would like to convert local coordinate system to lat/lon
> coordinate system. We can provide rules to convert, but how do you store all
> this in PostGIS?
>
> Regards,
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