[Qgis-user] QGIS reprojection broken?

[Brent Wood]

Hi,

Apologies for an attachment to a list email, but I kept it small...


The attached  image shows some Antarctic data (grounding line & ice shelf extent) with a polygon overlayed. 
I created the polygon by editing a text (csv) file with lat/longs:
x,y
150,-60
150,-85
255,-85
255,-60

I opened it in QGIS (CRS=EPSG:4326) & created a new polygon shapefile layer (snapping to the points) to create a box defined by the same points.

Then I opened the Antacrctic layers (WFS from NSIDC http://nsidc.org/cgi-bin/atlas_south in EPSG:3031 - Antarctic Polar Stereographic)

 
I set the QGIS project CRS to a user defined one, same as EPSG:3031, but with +lon_0=180 instead of 0 which gives a 180 up map instead of 0 up.

The map is displayed as in the attached image - a strange box is drawn to the north of the box polygon, the eastern points & vertices do not appear - and if the layer is editable, they cannot be clicked on as nodes. 

If I swap the CRS to EPSG:3031, the inverted map renders the box better (no extra box outside it) but the points are still rendered in a different location to the polygon vertices - but they share the same coordinates.

I can usually work around 180 issues in QGIS by using longitudes in the 0-360 space, but it seems to me that there are some issues with QGIS working in a polar projection across 180.

Does anyone know if there is a way to solve this, or is this an inherent problem for now? In the short term I need to decide whether or not I can progress with QGIS in the cross 180 polar space, or will need to find another tool.

In the longer term, if this is an issue, I'd like to work with a developer to resolve it - and may be able to fund (some of?) the work required.


Thanks,

   Brent Wood
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