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

GRASS GRASS developer
,
1

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?

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?

  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.

  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?

  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.

  5. It is my understanding that GRASS data output directory is not related to GDAL/PROJ. This is native GRASS format and the GRASS engine displays the data on the panel using some inbuilt functions.

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

Regards,

Kavitesh Singh

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2

On Wed, Apr 8, 2009 at 1:52 PM, <kavitesh.singh@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

3

Hi Markus,

Thank you for prompt reply. I would like to further ask you few more questions, and sure you would overlook my ignorance.

My requirement is to make a strip down GIS tool using GRASS engine focusing on raster image for the time being and preferably on windows platform.

I would prefer to use the GRASS data format so that I am not bounded on any commercial file format for my application and also provide user the option to use GRASS or Quantum GIS.

Please highlight the following doubts:

  1. The grass would be providing me APIs where in I can take any raster image, geo-reference it and then store in GRASS’s native format. Can you please point out to the modules I would require just to perform this action?

  2. Once I have converted to the GRASS native format, I would like to display the image in visual form. Now you have pointed to several options available with the existing version. I wanted to know is the display eventually like a photo viewer especially when GRASS is layering the information one over another. Also would grass provide me some standardized output in terms of jpg, bmp etc which I can display in any application? Any pointers to the similar options available on windows platform?

  1. 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 geo-coded incl. metadata, this is respected. Otherwise it

is imported as XY map.

So if the information is geo-coded already, GRASS would not perform any additionally operation but will still convert and store in the native format. Correct?

Additionally, if I have to display a GDAL processed input, does GRASS let me do that? Or are there tools which will help me see and understand what exactly is the output. (I hope I am able to present my point)

It is my understanding, that OGR would be similar to GDAL with focus on the vector data, which is further converted to the GRASS native format for processing and viewing.

I have worked mostly on windows platform, hence there are lot of questions as GRASS is based on Linux and current winGrass version is using the cygwin. Though I was reading the full windows version would be out soon.

The architecture diagram was really helpful in getting the overall idea of where all libraries fit in.

Thanks a lot…

Regards,

Kavitesh Singh

-----Original Message-----
From: neteler.osgeo@gmail.com [mailto:neteler.osgeo@gmail.com] On Behalf Of Markus Neteler
Sent: Wednesday, April 08, 2009 06:52 PM
To: Kavitesh Singh
Cc: GRASS developers list
Subject: Re: [GRASS-dev] GDAL/Proj modules role in Grass

On Wed, Apr 8, 2009 at 1:52 PM, kavitesh.singh@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

  1. 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.

  1. 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/

  1. 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.

  1. 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

Please do not print this email unless it is absolutely necessary.

The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately and destroy all copies of this message and any attachments.

WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email.

www.wipro.com

4

hi Kavitesh,

On Wed, Apr 8, 2009 at 4:50 PM, <kavitesh.singh@wipro.com> wrote:

Hi Markus,

Thank you for prompt reply. I would like to further ask you few more
questions, and sure you would overlook my ignorance.

no problem - also others are invited to contribute of course :slight_smile:

My requirement is to make a strip down GIS tool using GRASS engine focusing
on raster image for the time being and preferably on windows platform.

Ok!
BTW: in case that you want a Web based solution, also consider WPS,
e.g. pyWPS:
http://pywps.wald.intevation.org/

Some working example also here:
http://pywps.ominiverdi.org/

I would prefer to use the GRASS data format so that I am not bounded on any
commercial file format for my application and also provide user the option
to use GRASS or Quantum GIS.

Perfect! (see also somewhat related
  http://blog.cleverelephant.ca/2009/04/esri-formats-back-to-future.html
)

BTW: Using the GDAL-GRASS plugin, you get the API to read and
write GRASS' raster and vector data to other formats.

r.in.gdal/r.out.gdal and v.in.gdal/v.out.gdal use GDAL to read/write
to other formats.
Also QGIS and other software packages make use of this interface.

Please highlight the following doubts:

1. The grass would be providing me APIs where in I can take any raster
image, geo-reference it and then store in GRASS’s native format. Can you
please point out to the modules I would require just to perform this action?

Perhaps you should consider the Python bindings if you like that language:
http://download.osgeo.org/grass/grass6_progman/
-> GRASS SWIG interface
      -> Python

It is not greatly documented but already used in the wxPython GUI:
gui/wxpython/

Relevant command (focusing on raster here): r.in.gdal

What do you really mean with geo-referencing? do you have scanned XY
data or so? Ideally your data come with metadata describing projection
and such. This is then respected by r.in.gdal and the imported map
written out to the GRASS native format,.

Option: just "register" the external map file as virtual map with r.external.
That's way faster of course.

2. Once I have converted to the GRASS native format, I would like to
display the image in visual form. Now you have pointed to several options
available with the existing version. I wanted to know is the display
eventually like a photo viewer especially when GRASS is layering the
information one over another.

Right, GRAS uses the layer concept.
Get transparency through g.pnmcomp.html

BTW: manual
http://grass.osgeo.org/grass64/manuals/html64_user/

Also would grass provide me some standardized
output in terms of jpg, bmp etc which I can display in any application? Any
pointers to the similar options available on windows platform?

No problem:
d.out.file
r.out.gdal

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.

About 30 formats or so are supported:
http://www.gdal.org/formats_list.html
(see "Creation" column)

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

So if the information is geo-coded already, GRASS would not perform any
additionally operation but will still convert and store in the native
format. Correct?

Right. Or see r.external for making an external map visible without really
importing it.

Or, use the GDAL-GRASS plugin and look at the map in native GRASS
format without exporting (faster of course).

Get the plugin from the GDAL site (or your preferred distribution)

Additionally, if I have to display a GDAL processed input, does GRASS let me
do that? Or are there tools which will help me see and understand what
exactly is the output. (I hope I am able to present my point)

Mhh, not entirely clear to me.

It is my understanding, that OGR would be similar to GDAL with focus on the
vector data, which is further converted to the GRASS native format for
processing and viewing.

Right.
"Small" difference: GRASS is using a topological vector format while
GDAL is non-topological. Both v.in.ogr (v.out.ogr) and the OGR-GRASS plugin
translate between these worlds.
E.g. also the ESRI SHAPE format is non-topological.

I have worked mostly on windows platform, hence there are lot of questions
as GRASS is based on Linux and current winGrass version is using the cygwin.
Though I was reading the full windows version would be out soon.

It's available since the other day, just download it here:

Stand-alone installer:
http://download.osgeo.org/grass/grass64/binary/mswindows/native/

OSGeo4W bundle:
http://trac.osgeo.org/osgeo4w/

The architecture diagram was really helpful in getting the overall idea of
where all libraries fit in.

Thanks a lot..

You are welcome.

best
Markus