[GRASS-dev] GDAL/Proj modules role in Grass

[Markus Neteler]

On Wed, Apr 8, 2009 at 1:52 PM,  <kavitesh.singh at wipro.com> wrote:
> Hi All,
>
>
>
> I am beginner at learning GRASS and was trying to understand the overall
> architecture of GRASS using various libraries like GDAL/PROJ etc.
>
>
>
> I wanted to know how GDAL and PROJ library fit into GRASS for raster
> processing of maps?

These libraries are requirements for GRASS (see more below).

> I would like to verify my understanding of GDAL with my current reading for
> raster format like JPEG,BMP
>
> 1.    It is used for geo-referencing any raster image by providing the
> corner file data. Does the geo-referencing internally call PROJ library to
> reference according to any particular datum?

It depends:
- yes for r.proj and v.proj
- no for i.rectify

> 2.    The input to the GDAL can be any raster format like BMP, GeoTIFF,
> TIFF, PNG etc. What would be the output format GDAL produces after it
> manipulates the original raster image.

If the input is geocoded incl. metadata, this is respected. Otherwise it
is imported as XY map.

> 3.    Once the output is generated, is it available for processing in the
> memory or it produces some file which is later read by GRASS for
> visualization?

GRASS is storing its files in its internal format (except for r.external and
v.external). So, yes, files are produced.

I have just drawn the GRASS architecture:

http://trac.osgeo.org/grass/browser/grass-web/trunk/images
-      grass6_arch.odg
-      grass6_arch.png
-      grass7_arch.odg
-      grass7_arch.png

(please improve!)

See also here:
http://download.osgeo.org/grass/grass6_progman/

> 4.    I wanted to know how GRASS uses the geo-referenced raster image for
> display. Is it using some 3rd party library or has developed a display panel
> specific to GIS needs.

There is both in different implementations:
- built-in display system (X11 based)
- Tcl based display system
- wxPython based display system
- Cairo based display system
- PS based display system
- PNG based display system
- HTML based display system

All of them are drivers.

> 5.    It is my understanding that GRASS data output directory is not related
> to GDAL/PROJ.

Right. It is called GISBASE. See
http://grass.osgeo.org/grass64/manuals/html64_user/helptext.html

> This is native GRASS format and the GRASS engine displays the
> data on the panel using some inbuilt functions.

Right.

> Please excuse me, if the questions have been asked before also. I would
> appreciate any help in this regard.

Hope this helps,
Markus