[GRASS5] Re: An internal db for GRASS

[Eric G . Miller]

On Sat, Feb 10, 2001 at 12:23:35PM -0800, Rich Shepard wrote:
> On Sat, 10 Feb 2001, Roger S. Miller wrote:
> 
> > Forgive my ignorance, but...
> 
> Roger,
> 
>   Welcome to my club! :-)
> 
> > Postgres handles geometric data -- points, circles, polylines, polygons
> > and so on -- and includes functions to determine if a point is in an
> > area, two lines intersect and others (but no sort of raster
> > functionality).  How different is that from handling spacial data
> > structures?  Are those structures something that for some reason
> > couldn't be addressed as a user-defined type?
> 
>   I know it does. When I brought this up months ago, I was told by those who
> I assume know much better than I, that it was not suitable for an arc-node
> format such as GRASS.
> 
>   Thinking about this just now, it occurs to me that we'd use points and
> arcs as graphic types. The problem is that postgres does not handle
> topology. What it would take to handle topology within postgres, GRASS or a
> separate (but tightly integrated) program is beyond my knowledge.
> 
>   Looking at ARC/Info export data, I see that vectors have attributes such
> as LPOLY, RPOLY and so on. Is this computationally too difficult to store in
> a postgres database along with each spatial arc or point? I don't know.
> 
>   Sure, raster data is handled well internally and we don't want/need to
> mess with that. But, multi-attribute sites data and vector data are a
> different story.

In theory, you could use postgresql to store *all* data.  I think the
only way it could work is to mostly *not* use the built-in geometric types 
and have some "middleware" for all I/O.  It would take a considerable
amount of effort to come up with a workable base schema (you'd need
extra catalog tables) and the "middleware" would have to have a lot of
smarts built in.  I have a conception of how to do this, but it is not
trivial.

-- 
Eric G. Miller <egm2 at jps.net>

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