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

[Roland Hill]

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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