[postgis-users] Raster Support...

[Alan]

Hi all,
New guy, first post - not much PostGIS experience but a lot of interest and
a lot of Arc(insertModuleNameHere) experience.

Raster is not just a format - it is, in effect, a GEOMETRY TYPE that models
"chunks" of a surface very effectively and efficiently.

What's "data-basey" about it? In a word: "indexing". Why should I have to
load a 3GB file into my GDI just to query a couple of hundred pixels
surrounding a particular vector? (If my base heights com from a DEM or TIN
or, (insert name of significant deity) forbid, a point cloud, and I have
building footprints with roof elevations I don't want to load the whole
raster to get a Building Height-Above-Ground.

What if all I wanted was just to access a "value" at one particular
location? What if I didn't want to "see" the raster, just use its "data"?

Also, I work in the Emergency Services / Homeland Security area and pictures
(as well as all kinds of other rasters) are a BIG TIME requirement so
management and relationships to other features becomes critical.

The other thing I've realised over the years that every vector becomes a
raster before we can see it (either on the screen or on paper). Since GIS
has (at least) two parts - Analysis & Visualisation - getting control of the
raster can only be a good thing. 

Cheers
AlanK


-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Saturday, 26 August 2006 6:06 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Raster Support...


Indeed, that was exactly my intent.  To get some answers!  I  
personally have had one use-case recently, which is similar to  
Stephen Marshall's point (1), moving some vector information into  
raster space, doing some analysis which is best done in raster space,  
then pulling results back into vector space.

There is nothing particularly "database"y about the use case (we  
utilize the features of the database itself hardly at all), but  
having the rasters in the database avoids an unpleasant bunch of  
scripting to dump data out to GRASS, run the analysis, stuff the  
results back in.  The database becomes an analysis integration  
environment.  There are lots of good arguments around that using a  
scripting environment like Python would be a better integration  
architecture though.

I still haven't found any raster use cases that actually leverage the  
unique aspects of the database environment (high speed random access  
to tuples, transactional integrity, complex data models).

Paul

On 25-Aug-06, at 12:58 PM, Stephen Woodbridge wrote:

> Jeff Hoffmann wrote:
>> Paul Ramsey wrote:
>>> To repeat:  once you get your rasters in the database, what are  
>>> you  going to do with them?
>
> Jeff,
>
> I think there are two ways to look at this statement. One is it  
> might be a dismissal, but I think the one that Paul is asking for  
> is What are your use cases, so he can collect them as you suggest.  
> It has been REALLY hard to get anyone to come forward with there  
> specific needs in this area, beside just asking for the feature.
>
> -Steve
>
>> I used to have that same question the same time anybody the topic  
>> got brought up.  I think that, if you try, you can come up with  
>> some ways raster data might be useful integrated into the database  
>> (even if it's not the best or only way of doing something).   
>> Perhaps too many people think of raster data as essentially  
>> photographic and not as a giant array of geo-referenced data  
>> points and they just dismiss it out of hand.  If you're just  
>> storing a bunch of photos in your database, I agree with the  
>> sentiment that it just makes your life difficult.  If, on the  
>> other hand, you have a DEM (for example) where the data points are  
>> elevation, you could query it to find the elevation at a point.   
>> Or take it a step further and add a Z coordinate to all that 2-D  
>> vector data in case you ever want to visualize it in 3-D.
>> I guess the first thing I'd do if I were that interested in adding  
>> raster support is collect a bunch of possible use cases and  
>> categorize them to figure out what sort of functionality people  
>> would be interested in seeing.  I think it'd be interesting to see  
>> what people would use it for & maybe would inspire some interest  
>> in the wider community.
>
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