[postgis-devel] [WKT Raster] Regular blocking in gdal2wktraster.py

[Pierre Racine]

Frank,

Type 4 is different than 1 and 2 in that:

-each image meets the regular contraints
-each image is stored as one separate table

This is the traditional GeoRaster way of storing images (e.g. landsat)
in a database.

Types 1 and 2 correspond better to the notion of a coverage (much like a
vector coverage):

-in type 1 the global extent is not necessarily rectangular (although we
could have an option to "force" it to be rectangular by adding
nodatavalue or empty tiles but this is from my point of view an
overcomplicated artefact)

-for both types, the source is composed of many raster files that most
be retiled and stored into the same db table

-another characteristic (which I did not mention) is that tiles might
not be all of the same size. I could, for example, have many 6030pixels
by 6030pixels images as source and want to store them as as many (3600
tiles of 100pixels x 100pixels and the rest as 60 30pixels x 100pixels
tiles,  60 100x30 tiles and one 30x30 tile).

As a GIS analyst working and doing analysis with raster coverage
(constructed by myself or downloaded), I meet types 1 and 2 much more
often than type 4. I want to be able to import case 1 and 2 in the
database without having to reconstruct a big raster using other tools.
Moreover it might be impossible to build rasters big enough to cover
very large extent (like Canada).

I understand that this goes beyond the traditional way we see rasters
and that this implies datastructure most applications are not prepared
to support yet but I think this is a great improvement over our
traditional usage of stricly rectangular rasters. It's with that in mind
that I designed WKT Raster.

If an application threats each rows of a raster table as a single raster
(as I have always try to sell WKT Raster "a tile is a raster and a
raster is a tile, there is no distinction") then the application should
not see any difference. As for a vector layer. I understand however that
applications prefers to load big rectangular complete tiled rasters but
this is very limitative and not very practical from an analytical point
of view.

My classical example is storing the SRTM coverage of Canada. It is not
and I don't want it to be rectangular, the (downloaded) source is
composed of many files and I can't build a single raster from it because
it's too big. I want to be able to import it's many files, retiled to
smallers tiles in a single table in a single loading command. With this
I would be very happy (and I guess many of our users) and I could begin
to do nice vector/raster analysis :-)

Pierre


>-----Original Message-----
>From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-
>bounces at postgis.refractions.net] On Behalf Of Frank Warmerdam
>Sent: 25 mars 2009 12:38
>To: PostGIS Development Discussion
>Subject: Re: [postgis-devel] [WKT Raster] Regular blocking in
gdal2wktraster.py
>
>2009/3/20 Pierre Racine <Pierre.Racine at sbf.ulaval.ca>:
>> Mateusz,
>>
>> As an image is worth a thousand word, I updated the PowerPoint to
better express the different
>raster datasets possibilities. Instead of the three categories
("continuous tiled coverage",
>> "vector-like discrete coverage" and "image warehouse") I created
five:
>>
>> 1 - As an incomplete non-overlapping tiled coverage
>> 2 - As a complete tiled non-overlapping tiled coverage
>> 3 - As a layer of vector like discrete raster objects
>> 4 - As a "big raster" (or a series of)
>> 5 - As an image warehouse
>
>Pierre,
>
>I would like to encourage treating cases 1 and 2 as the same thing.
>It was never my intention that the regular blocking would require a
>complete set of tiles.   Missing tiles would just be treated as the
>nodata value, or zero if there is no nodata value.
>
>I will attempt to update the RASTER_COLUMNS document to reflect
>this.
>
>I'm also still failing to grasp how 4 (big raster) is distinct from
>the 1/2 case.
>
>Best regards,
>--
>---------------------------------------+-------------------------------
-------
>I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
>light and sound - activate the windows | http://pobox.com/~warmerdam
>and watch the world go round - Rush    | Geospatial Programmer for Rent
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