[postgis-users] General Question on Raster within PostGIS

[Roger Bedell]

Hisaji,
 
Thank you for your reply. The reason I am asking, is that I think a
general purpose raster implementation for PostGIS would be useful. I put
together a similar scheme for our SylvanMaps OCX product long ago (1996
or so), which works well, and is very simple. The difference between
mine and yours are that the image is actually held in the database in a
BLOB field. (Actually, large images are split into tiles), and no affine
transform is specified. 
 
The consumer of the image data would request just those tiles needed.
The consumer (or hopefully PostGIS) would be responsible for
projecting/tiling/resampling/resizing the image for display or analysis.
 
Additionally, several tables can be used, each with successively lower
resolution images (resampled), so that if a consumer requested a large
area, she would not be inundated with thousands of tiles.
 
If the blobs were simply JPEG2000 tiles, the compression would approach
MrSID compression numbers.
 
Advantages of this approach:
 
1)       Really huge images can all be stored in the database.
2)       The database could handle all the mundane details of
projection, retiling, resizing etc.
3)       Compression using JPEG2K is public domain, and quite good.
4)       No need to have thousands of GeoTIFF or GeoJPEG, or MrSID files
hanging around.
 
Questions:
1)       I'm not sure what the affine transform is used for?
2)       Is there a BLOB field in PostGIS?
 
Roger
 
Roger Bedell, President, Sylvan Ascent Inc.
roger at sylvanmaps.com
www.sylvanmaps.com
www.topodepot.com
505-758-7712
 
-----Original Message-----
From: postgis-users-admin at postgis.refractions.net
[mailto:postgis-users-admin at postgis.refractions.net] On Behalf Of Hisaji
ONO
Sent: Thursday, May 09, 2002 8:51 AM
To: postgis-users at postgis.refractions.net
Subject: Re: [postgis-users] General Question on Raster within PostGIS
 
>Hi Everyone, 
>
>I'm new to this list, so please excuse this if it has already been
answered.
>
>How are people storing raster images (satellite, aerial photos etc)
within PostGIS?
 
Hello.

 Currently, PostGIS doesn't support dealing with images. So, I used
PostGIS's Geometry Type as a refrence or retrieval for exaternal aerila
photo in the following manner for outputing SVG instances by PHP.


             Table "airphoto"
 Attribute |       Type        
-----------+-------------------+
 geoid     | integer           |
 geo_value | geometry          |
 urlname   | character varying |
 ox        | double precision  |
 oy        | double precision  |
 width     | double precision  |
 height    | double precision  |
 a         | double precision  |
 b         | double precision  |
 c         | double precision  |
 d         | double precision  |
 e         | double precision  |
 f         | double precision  |

 where "geo_value" is polygons which is extent of images, "urlname" is
URL  of images,  "ox" and "oy" are origin coordinate in pixel, "width"
and "height" are literally images' ones in pixel, "a" - "f" are
parameters of affine tranformation for images deriving from world files

 I show followin' examples.

 geoid |                                        geo_value
                  |    urlname    | ox | oy | width | height |  a  | b |
c |  d  |   e    |   f
-------+----------------------------------------------------------------
--------
------------------+---------------+----+----+-------+--------+-----+---+
---+------+--------+--------
     0 | SRID=-1;POLYGON((-13000 -33750,-13000 -33000,-12000
-33000,-12000 -3375
0,-13000 -33750)) | 9ld1622_o.jpg |  0 |  0 |  5000 |   3750 | 0.2 | 0 |
0 | -0.
2 | -13000 | -33000
     1 | SRID=-1;POLYGON((-13000 -34500,-13000 -33750,-12000
-33750,-12000 -3450
0,-13000 -34500)) | 9ld1624_o.jpg |  0 |  0 |  5000 |   3750 | 0.2 | 0 |
0 | -0.
2 | -13000 | -33750

 I hope this will help you.
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