[Qgis-user] Support for (wrong) GEOCOVER projection for S hemisphere in qgis

[Agustin Lobo]

No, what I was doing was different:
I was setting the project to 18S (not 18N) with OTF reprojection, the raster to 18N
and the vector layers got reprojected to 18S but the raster
was not displayed.
I was expecting the raster to be located in the S hemisphere because
the coordinates are negative. In TNTmips, as the coordinates are negative, even 
if the raster CRS is set
to 18N, the raster is displayed in the S hemisphere. Not sure if this
is what qgis should do, though, as we are dealing with wrongly annotated
raster layers: in UTM, S is S, not negative N.

On the other hand, I assumed that if you set the project to 18N, then the vector 
layers would projected to the N hemisphere.
But have tried defining the project as 18N as you say, used Coordinate capture 
to check lon,lat, and actually get correct lon,lat coordinates (in the S
hemisphere). The vector layers are reprojected to
18, no matter the S or N, the original latitude correctly defines the hemisphere.

So it works "your way", thanks!

Agus



Micha Silver wrote:
> Hi Agus:
> I am actually able to do just that. I also am using some Landsat 
> GEOCover images from below the equator, projected, as you say in UTM 39_N_.
> I load the raster, set the project CRS to that (UTM Northern) 
> projection, and enable OTF projection. Then I can overlay vector layers, 
> which are WGS84 Lon-Lat., and they are correctly located.
> 
> It's usually not very helpful to say "works for me" but...
> Anyway, HTH,
> Micha
> 
> 
> Agustin Lobo wrote:
>> The global set of Landsat images on GEOCOVER
>> https://zulu.ssc.nasa.gov/mrsid/mrsid.pl
>> is on UTM/WGS projection
>> but with the Southern hemisphere tiles as UTM zones in the N with
>> negative coordinates. For example, a tile that should be at 18S is
>> actually 18N with negative coordinates
>> ("Non-standard UTM definition: For the southern hemisphere, the 
>> GeoTiff files
>>   contain positive zone numbers with negative northing coordinates")
>> https://zulu.ssc.nasa.gov/mrsid/docs/GeoCover_circa_2000_Product_Description.pdf 
>>
>>
>> As we have some vector layers on geographic coordinates WGS84 and a 
>> Geocover tile for 18S,
>> I've set the project as 18S, enabled CRS reprojection on the fly, and set
>> the raster CRS to 18N. Unfortunately, QGIS does not display the 
>> raster, even
>> selecting zoom to layer extent. (Using Mimas).
>>
>> This is probably not a problem of QGIS, the Geocover projection is 
>> just wrong,
>> but would like to know if there could be a way to circumvent this 
>> problem to
>> be able to use GEOCOVER tiles of the S hemisphere within QGIS.
>> A way could be making a world file with the Georeferencer plugin, but 
>> perhaps
>> there is a more general way.
>>
>> Thanks
>>
>> Agus
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