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

[Agustin Lobo]

Thanks Roland,
I agree that a solution like this is the best: put the
data in the correct projection.

Agus


Roland Hill wrote:
> I have had the same problem with southern hemisphere Landsat being
> registered as northern hemisphere with negative northings. The best
> solution I found was to reproject the image. You can use GDAL with
> something like
> 
> gdalwarp -t_srs '+proj=utm +zone=34 +south +datum=WGS84' -srcnodata 0
> -dstnodata 0 -multi -of GTiff -co COMPRESS=LZW -co TFW=true -co
> INTERLEAVE=BAND $1 Z34S_$1
> 
> where $1 is the name of the original file (the output file has Z34S_
> prepended). I just put this into a script file and call it from the
> command line, or from another script if you have a list of images to
> convert.
> 
> Regards,
> 
> Roland
> 
> 
> Micha Silver wrote:
>> Agustin Lobo wrote:
>>
>>> 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.
>> Since QGIS doesn't deal with on-the-fly reprojection of rasters, we 
>> know that you have to set the project CRS to whatever projection the 
>> raster is in. In this case, since the Landsat are (wrongly) set to UTM 
>> N, I guess you have to stay with that in order for vectors to be 
>> properly registered.
>> Cheers,
>> Micha
>>> 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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