RES: [postgis-users] Support for Raster Data

[Vortex]

On Mon, 18 Apr 2005 10:57:24 -0300
"Gustavo Henrique Sberze Ribas" <gribas at cpqd.com.br> wrote:

> > Does PostGIS have support for Raster Data? If som how could I 
> > acheive that?
> 
>   What do you mean by support? You can't store your raster data in a geometry
> column if that's what you're asking. What you can do is store the raster as a 
> blob and use the geometry column to store its outline as a Polygon.

I'm new to the List and haven't read the original article
but i'm interested in this topic too.

I don't want to only store the data as blob but
would like to work with the data. For example
making a query to get height information of
a specific location out of the srtm rasterdata,
building a 3d plane polygon which is
aproximated to the average height level of
a small area, computing "line of sight"
or something like that. How can this be
achieved?

With the GDAL Library there comes a tool
called gdal_contour. I'm not familiar with this
but it looks like it would produce 2D contour
lines associated to a numeric height level.
I don't know if this is a feasible way to
get raster data into postgis. Especially with
really large amounts of Data (complete SRTM Data).

I suppose the produced lines are always
closed line paths? So i can get the height
level of a specific location by doing
a query to the bounding box of the contour
lines and find the maximum with a max()
aggregate function on the elevation
column? Using an index search this should
quite fast. But i'm new to all this
openGIS stuff and perhaps this idea
is completely braindead?
At least it sounds not very efficient and i
expect a much faster access from a direct
query on the raster data. But i haven't any
idea to do this or at least don't know how
to interface it to postgis.

Any suggestions?


Klaus

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