Re: [Qgis-user] reposting q on reprojection problem in QGIS > 2.0

[Peter Aldhous]

Dear Andre,

Thanks for your reply. I was optimistic that this would work, but sadly
it does not. I've tried creating various polygons, and running either
clip or difference. Even if I cut the world shapefile 5 degrees away
from 180E/W, I'm still getting the bizarre trapezoid behavior on
reprojection to Robinson in QGIS.

ogr3ogr in the command line works fine, and there I don't need to clip,
the reprojection works and the shapefile loads perfectly in QGIS. So
this is fine for my purposes, but it does seem that something has gone
awry with reprojection in the latest version of QGIS for the Mac. Which
will be a shame when I come to teach it.

Best wishes,

Peter




Peter Aldhous, PhD
Science journalist
Contributor, MATTER 
phone: 415 800 3471
cell: 415 503 7323
email: pe...@peteraldhous.com 
web: www.peteraldhous.com 
twitter: @paldhous 
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Re: [Qgis-user] reposting q on reprojection problem in QGIS > 2.0

[Andre Joost]

Am 01.07.2014 14:48, schrieb Peter Aldhous:


Hi all,

Apologies for reviving this thread (below), but does anyone have a
solution other than using a different data format? I ask because I will
be do some teaching using QGIS and want to work with shapefiles for that.

This is a problem that's emerged for me only with recent versions of
QGIS, so something must have changed to cause the behavior. Might it be
at the level of GDAL?



A simple solution is to cut the data at 180°E/W.
I described  a detailed workflow for QGIS or GDAL here:


http://gis.stackexchange.com/questions/102009/convert-shapefiles-from-wgs84-to-miller-projection

HTH,
André Joost

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[Qgis-user] reposting q on reprojection problem in QGIS > 2.0

[Peter Aldhous]

Hi all,

Apologies for reviving this thread (below), but does anyone have a
solution other than using a different data format? I ask because I will
be do some teaching using QGIS and want to work with shapefiles for that.

This is a problem that's emerged for me only with recent versions of
QGIS, so something must have changed to cause the behavior. Might it be
at the level of GDAL?

Best wishes,

Peter




-- 
Peter Aldhous, PhD
Science journalist
Contributor, MATTER 
phone: 415 800 3471
cell: 415 503 7323
email: pe...@peteraldhous.com 
web: www.peteraldhous.com 
twitter: @paldhous 

I can verify this same behavior on Win7 with QGIS 2.4 64b. I think it 
has to do with the shapes crossing the 180^(o) line. If you zoom in to 
a smaller area that includes only countries in one hemisphere, the 
borders look OK. Also, it's not only Robinson and Mollweide: any 
global projection will show strange trapezoids (even "Google" mercator)
I also see that if you use the *spatialite database file* from 
naturalearthdata.org this problem disappears. You can switch to other 
world projections with no problem.

On 29/06/2014 16:59, Peter Aldhous wrote:

> I don't think the image came through, but the problem is that every 
> polygon ends up as a trapezoid, so I end up with a collection of 
> overlapping trapezoids
>
> Peter Aldhous, PhD
> Science journalist
> Contributor, MATTER 
> phone: 415 800 3471
> cell: 415 503 7323
> email: pe...@peteraldhous.com 
> web: www.peteraldhous.com 
> twitter: @paldhous 
>
> On 6/29/14, 6:54 AM, Peter Aldhous wrote:
>> Hi all,
>>
>> I'm using the KyngChaos install of QGIS on the Mac (Mavericks and 
>> Lion, on different machines), and I've been having problems with  
>> projections including Robinson and Mollweide from QGIS 2.2 onwards.
>>
>> Everything was fine in QGIS 2.0, but in 2.2 and 2.4, re-projecting a 
>> world Natural Earth shapefile to a Robinson projection, for example, 
>> gives this:
>>
>>   Any idea what might be going on, and how to fix it?
>>
>> Thanks,
>>
>>
>> -- 
>> Peter Aldhous, PhD
>> Science journalist
>> Contributor, MATTER 
>> phone: 415 800 3471
>> cell: 415 503 7323
>> email: pe...@peteraldhous.com 
>> web: www.peteraldhous.com 
>> twitter: @paldhous 
>>

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