[Qgis-user] Reprojection issue QGis 1.8

[Lester Anderson]

I have not heard of debug mode, how is that activated?

I think the problem must lie with the edge limit being exactly at -180. I
have a GeoTiff raster from a much smaller area, in the same UTM zone, and
it went into a Geographic (lat/long) CRS and reprojected no problem.

Basically load the raster into the project, tell it what the native CRS and
then it's in there. I think a test, like you suggest, of clipping a bit of
the edge to see if that really is the cause of the issue. Probably also
worth checking vectors too, as that would help to siolate in the code where
the problem lay, if indeed it is a problem.

Most of the GeoTIff's I make have the projection information in the file
itself, and this works fine with reprojection etc.

I know that on the fly reprojection works fine with rasters in general as I
often load up global grids and switch from Geographic to Mollweide or Polar
etc and those have no problems. So the underlying code is fine from that
perspective. In the past, I have found that some "problems" can arise if
the longitude definition is different, i.e. 0-360 instead of -180/+180.

Cheers
Lester


On 1 September 2013 02:54, Alex Mandel <tech_dev at wildintellect.com> wrote:

> It has since 1.7
> http://linfiniti.com/2011/03/on-the-fly-raster-reprojection-comes-to-qgis/
>
> However stuff next to the edge of Lat/Lon coordinate systems is
> perpetually an issue in a lot of GIS software. Sometimes I cut off my
> stuff to only go to -179, sometimes I slice my stuff at the boundary
> into separate images. There are all sorts of possible workarounds.
> Generally I find actual reprojection is better than on-the-fly.
>
> I'm wondering if the data in question here has an incorrect projection
> definition or just needs a little shaved off the edge to behave right.
>
> Are you running in Debug mode by any chance? (Outputs more information
> on crashes) Willing to try it on the soon to be released version?
>
> Thanks,
> Alex
>
>
> On 08/31/2013 05:41 PM, Matt Boyd wrote:
> > Not really a solution, but, I didn't think that on the fly reprojection
> of
> > rasters was supported by qgis. I'd be really happy to be corrected
> though.
> >
> > Matt
> > On Aug 31, 2013 11:47 PM, "Lester Anderson" <arctica1963 at gmail.com>
> wrote:
> >
> >> Hello,
> >>
> >> I have a raster file (GeoTIFF and netCDF grid) of the Tonga region, so
> has
> >> the longitude/latitude limits like:
> >> -180 to -170; -26 to -12
> >>
> >> I used GMT to reproject the original Geographic grid from WGS84 to UTM
> >> Zone 1S (WGS84), and created a GeoTIFF of the data. Both files will load
> >> into a new project file no problem.
> >>
> >> However, if the project CRS is changed to say Geographic again (WGS84),
> >> QGIS will crash  with the following error message:
> >>
> >>
> >>
> >> The whole thing just hangs and the only way to quit, is to kill it via
> the
> >> Task Manager.
> >>
> >> If on-the-fly transform is set, then as long as the program knows what
> >> projection each layer is, be it vector or raster, then it should be
> able to
> >> transform it. When loading the raster in I ensured it had the correct
> >> spatial attribution, so that is not the problem.
> >>
> >> The same error occurs if I load the same raster (or grid) into a project
> >> in Geographic coordinates. Another GeoTIFF with the same projection (and
> >> from the same UTMzone) loads fine.
> >>
> >> Is there an issue transforming data close to 180 degrees?
> >>
> >> Any ideas?
> >>
> >> Cheers
> >> Lester
> >>
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> >
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