[GRASS-user] exporting single banded float raster to true color geotiff (i.e. 3 Byte bands with color interpretation)

GRASS GRASS user
1

Giovanni wrote:

The question is the object :)I have a Float raster which GRASS
displays with a certain color table (I haven't set it...
PS: what table is used by default?). What's the most effective
way to export the raster into a true color Geotiff (as a 3 Byte
bands with color interpretation) using a certain color table?

I believe that r.out.tiff will export using colors, not data.
Add the -t flag to get a world file & so make it a geotiff.

In GRASS 6.4 the d.out.file module is another option, set the
size= parameter to the number of rows and columns, and select
format=geotiff.

The default color table is "rainbow", see the r.colors help page
for details.

Hamish

2

Thanks Hamish, r.out.tiff did the work. I already had tried it but I failed because I dind’t set the region correctly.
Anyway, setting the -t flag writes the TFW but doesn’t make it a true GTiff, because r.out.tiff writes a Baseline tiff, without the GTiff tags. But that isn’t a problem of course, I can produce a GTiff with another step (eg gdal tools).

giovanni

2011/9/17 Hamish <hamish_b@yahoo.com>

Giovanni wrote:

The question is the object :)I have a Float raster which GRASS
displays with a certain color table (I haven’t set it…
PS: what table is used by default?). What’s the most effective
way to export the raster into a true color Geotiff (as a 3 Byte
bands with color interpretation) using a certain color table?

I believe that r.out.tiff will export using colors, not data.
Add the -t flag to get a world file & so make it a geotiff.

In GRASS 6.4 the d.out.file module is another option, set the
size= parameter to the number of rows and columns, and select
format=geotiff.

The default color table is “rainbow”, see the r.colors help page
for details.

Hamish

3

On Mon, Sep 19, 2011 at 11:15 AM, G. Allegri <giohappy@gmail.com> wrote:

Thanks Hamish, r.out.tiff did the work. I already had tried it but I failed
because I dind't set the region correctly.
Anyway, setting the -t flag writes the TFW but doesn't make it a *true*
GTiff, because r.out.tiff writes a Baseline tiff, without the GTiff tags.
But that isn't a problem of course, I can produce a GTiff with another step
(eg gdal tools).

You can export a true GTiff with color as cell values instead of
original cell values with

# extract RGB values
r.mapcalc "mymap.r = r#mymap; mymap.g = g#mymap; mymap.b = b#mymap"

# create RGB group
i.group group=mymap.rgb in=mymap.r,mymap.g,mymap.b

# export RGB group
r.out.gdal in=mymap.rgb out=mymap.tif -c

The -c flag to skip export of the colortable because the raster values
themselves hold the color info.

Markus M

giovanni

2011/9/17 Hamish <hamish_b@yahoo.com>

Giovanni wrote:
> The question is the object :)I have a Float raster which GRASS
> displays with a certain color table (I haven't set it...
> PS: what table is used by default?). What's the most effective
> way to export the raster into a true color Geotiff (as a 3 Byte
> bands with color interpretation) using a certain color table?

I believe that r.out.tiff will export using colors, not data.
Add the -t flag to get a world file & so make it a geotiff.

In GRASS 6.4 the d.out.file module is another option, set the
size= parameter to the number of rows and columns, and select
format=geotiff.

The default color table is "rainbow", see the r.colors help page
for details.

Hamish

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4

I Thanks Markus, I didn’t know I could export image groups directly from r.out.gdal. The GUI doesn’t list image groups from the available inputs… I will tell Martin.

giovanni

2011/9/19 Markus Metz <markus.metz.giswork@googlemail.com>

On Mon, Sep 19, 2011 at 11:15 AM, G. Allegri <giohappy@gmail.com> wrote:

Thanks Hamish, r.out.tiff did the work. I already had tried it but I failed
because I dind’t set the region correctly.
Anyway, setting the -t flag writes the TFW but doesn’t make it a true
GTiff, because r.out.tiff writes a Baseline tiff, without the GTiff tags.
But that isn’t a problem of course, I can produce a GTiff with another step
(eg gdal tools).

You can export a true GTiff with color as cell values instead of
original cell values with

extract RGB values

r.mapcalc “mymap.r = r#mymap; mymap.g = g#mymap; mymap.b = b#mymap”

create RGB group

i.group group=mymap.rgb in=mymap.r,mymap.g,mymap.b

export RGB group

r.out.gdal in=mymap.rgb out=mymap.tif -c

The -c flag to skip export of the colortable because the raster values
themselves hold the color info.

Markus M

giovanni

2011/9/17 Hamish <hamish_b@yahoo.com>

Giovanni wrote:

The question is the object :)I have a Float raster which GRASS
displays with a certain color table (I haven’t set it…
PS: what table is used by default?). What’s the most effective
way to export the raster into a true color Geotiff (as a 3 Byte
bands with color interpretation) using a certain color table?

I believe that r.out.tiff will export using colors, not data.
Add the -t flag to get a world file & so make it a geotiff.

In GRASS 6.4 the d.out.file module is another option, set the
size= parameter to the number of rows and columns, and select
format=geotiff.

The default color table is “rainbow”, see the r.colors help page
for details.

Hamish

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