[gradsusr] Generating image overlay for Open Street Map / Mercator Projection

[Angelo Bertozzi]

hi
I've a method for producing map overlay with Grads in mercator projection,
but is not so straightforward

i'm starting from rotated lat-lon or lambert conformal preprojected data in
grib files
1) remove pdef directives in ctl files and sobstitute the "linear"
progression in xdef and ydef with "levels" directive with the list of
latitudes (ydef) and longitudes (xdef) of any single grid nodes
This steps in my case is producing a huge .ctl files (the grib ctl files
describing a 1600x2000 grid); a perl text-manipulation script is doing this
work
2) plot a tiff image with "set gxout kml",
3) converting and rescaling with imagemagick the *tiff image in PNG




2012/6/5 Jonas Kaufmann <me at j0nes.de>

> Hello,
>
> do you have an idea how to use 'set gxout geotiff' to generate
> displayable PNG images for use on a map software? Or do you have any
> other hints how Mercator projection in GrADS works?
>
> Thank you for your help!
>
> Jonas
>
> On Fri, Jun 1, 2012 at 10:55 AM, Jonas Kaufmann <me at j0nes.de> wrote:
> > Hello,
> >
> > thank you for your answer! Too bad there is no support for Mercator
> > projection available (yet).
> >
> > I just had a look at the GeoTIFF output, but I did not succeed in
> > creating a PNG (or whatever) file that I could overlay on OSM or
> > Google Maps. The tif file gets created, but it is looking almost
> > completely black when viewing with an image viewer (but I think this
> > is expected behaviour?). I have tried to convert it to PNG using the
> > GDAL tools with gdal_translate, but I only get grayscale noise images.
> >
> > Can someone explain the correct workflow to go from 'set gxout
> > geotiff' to a displayable PNG image?
> >
> > Thank you for your help!
> >
> >
> > Jonas
> >
> >
> > On Thu, May 31, 2012 at 5:05 PM, Chris Slocum
> > <cslocum at atmos.colostate.edu> wrote:
> >> Hi Jonas,
> >>
> >> I too have been looking for a Mercator projection to
> >> use with something like Open Street Map. To date,
> >> I do not think there is a public extension for a Mercator
> >> projection but the idea has been bounced around.
> >>
> >> I know that Weather Underground had someone
> >> develop the projection for their WunderMap so it
> >> is possible to do.
> >>
> >> In the interim, you could look at the GeoTIFF option.
> >>
> >> -Chris
> >>
> >>
> >>
> >> On Thu, May 31, 2012 at 6:46 AM, Jonas Kaufmann <me at j0nes.de> wrote:
> >>>
> >>> Hello,
> >>>
> >>> I am trying to generate an image with GrADS that should cover the
> >>> whole world. The image should be based on an forecast from the GFS
> >>> model. I want to use this image as a layer on top of Open Street Map.
> >>>
> >>> I can already create an image without borders, labels etc that I can
> >>> put on my map. However it seems that the projection still is wrong,
> >>> e.g. the continent borders drawn by GrADS do not match the borders on
> >>> the map. I think this might be related to the map projection used, in
> >>> OSM this should be Mercator projection which is not available in
> >>> GrADS. The complete script can be found at the bottom of the mail.
> >>>
> >>> Is there a way to make the forecast map fit on OSM?
> >>>
> >>>
> >>> Thank you for your help!
> >>>
> >>>
> >>> Jonas
> >>>
> >>>
> >>> -------
> >>>
> >>> 'open gfs'
> >>>
> >>> 'set gxout shaded'
> >>> 'set parea 0 11 0 8.5'
> >>> 'set mpdraw off'
> >>> 'set frame off'
> >>> 'set xlab off'
> >>> 'set ylab off'
> >>> 'set mproj latlon'
> >>> 'set grads off'
> >>>
> >>> 'set mpdset hires'
> >>> 'set map 1 1 1'
> >>>
> >>> 'set lon -180 180'
> >>> 'set lat -90 90'
> >>>
> >>> 'd mag(ugrd10m, vgrd10m)'
> >>>
> >>> 'printim world.png x512 y512'
> >>> 'quit'
> >>> _______________________________________________
> >>> gradsusr mailing list
> >>> gradsusr at gradsusr.org
> >>> http://gradsusr.org/mailman/listinfo/gradsusr
> >>
> >>
> >>
> >> _______________________________________________
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> >>
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*Bertozzi Angelo*
Meteorologist - HPCC admin & research
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