[gdal-dev] How to convert a GIF (being a grid with value in channel B from RGB) to XYZ?

[Chaitanya kumar CH]

If the transformation is just shifting and scaling you can set the
GeoTransform element in the VRT file.
You can scale the pixel values using the Offset and Scale elements.

On Mon, Jul 25, 2011 at 5:24 PM, Stefan Keller <sfkeller at gmail.com> wrote:

> Hi Chaitanya kumar
>
> Many thanks for the hints. I kow VRT from OGR but was not sure if this
> works here too.
>
> What I'm still wondering is, how to accomplish the transformation.
> It's rather a coord. translation process not comparable to warping:
>
> > The GIF size (= grid size) is 400x400 pixel with a cell size of 1000m.
> > The following is known about the geolocation (Switzerland,
> > EPSG:21781/CH1903): xmin: 481000, ymin: 38000 and xmax: 881000, ymax:
> > 438000.
>
> So I'd like to do some shifting and scaling before XY-coordinates are
> output (Z coming from the Colortable).
>
> Yours, S.
>
>
> 2011/7/25 Chaitanya kumar CH <chaitanya.ch at gmail.com>:
> > Stefan,
> >
> > You can convert the integer codes to float values using a VRT file[1] for
> > each gif file.
> > Create a VRT file with the ColorTable element. Add the SimpleSource to
> point
> > to your gif and the SourceBand element as 3 to point to B band.
> >
> > Once you create a VRT file for the GIF, you can use it like any other
> raster
> > file. GDAL interprets the elements in it and applies the conversions
> > internally. Use it with gdal_translate or gdalwarp (if you want to warp
> it
> > to a new coordinate system) to create an ASCII Grid file.
> >
> > [1]: http://www.gdal.org/gdal_vrttut.html
> >
> > On Mon, Jul 25, 2011 at 12:39 AM, Stefan Keller <sfkeller at gmail.com>
> wrote:
> >>
> >> I have a raster/grid file transformation and conversion question:
> >>
> >> The input are hunddrets of GIF files which in fact are a grid about
> >> rainfall observations. The files have 8 BitsPerPixel (0..255). The B
> >> channel (integer value) from RGB obviously represents the
> >> precipitation intensity in [mm/h] according to a lookup table (0=>0,
> >> 1=>0.2, 2=>0.32, 3=>0.5, 4=>0.8, 5=1.3, 6=>2, 7=>5, 8=>8 9=>13 10=>20,
> >> 11=>32, 12=>50, 13=>50, 14=>80, 15=>130).
> >>
> >> The GIF size (= grid size) is 400x400 pixel with a cell size of 1000m.
> >> The following is known about the geolocation (Switzerland,
> >> EPSG:21781/CH1903): xmin: 481000, ymin: 38000 and xmax: 881000, ymax:
> >> 438000.
> >>
> >> The target format is ASCII Gridded (XYZ)? or Arc/Info ASCII Grid
> >> (AAIGrid), with e.g. the following on each line: "481000 38000 0.32",
> >> meaning the transformed coordinates x and y and the float value (as
> >> indicated above in the lookup table).
> >>
> >> I know OGR but I'm new to GDAL: How would you accomplish this task?
> >>
> >> Transforming with gdal_transform then converting with gdal_translate ?
> >> Or do I have to write something myself (perhaps based on gdal2xyz.py)?
> >>
> >> -S.
> >> _______________________________________________
> >> gdal-dev mailing list
> >> gdal-dev at lists.osgeo.org
> >> http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
> >
> >
> > --
> > Best regards,
> > Chaitanya kumar CH.
> >
> > +91-9494447584
> > 17.2416N 80.1426E
> >
>



-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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