[Qgis-developer] Area calculation issues

[Neumann, Andreas]

Dear Nyall, 

Thank you so much for analyzing the issue and also thank you in advance
for porting the fix to 2.18! 

I opened the sample project with 2.14 and I can confirm that the area
values of both planimetric and ellipsoidic area calculations are very
close for all features. 

It is very much appreciated! 

Thanks, 

Andreas 

On 2017-02-03 01:36, Nyall Dawson wrote:

> On 1 February 2017 at 19:55, Neumann, Andreas <a.neumann at carto.net> wrote: 
> 
>> Hi Nyall,
>> 
>> Thanks for the explanations. I should have read the explanations of the help text more closely. It explains it all.
>> 
>> However, there still seem to be issues. Consider the following results below. First column is the result of $area, second column is area($geometry).
>> 
>> Sometimes the results are very close, in other cases the difference is massive. Like in the very first row. 32'087 vs 190'605'589 square meters. This can't be explained with ellipsoidical vs. planimetric. In this first row, the result of area($geometry) (planimetric) seems correct, while the ellipsoidical result ($area) is massively wrong.
>> 
>> How can this huge difference be explained?
> 
> Ok - I've looked into this. It's not an issue in 2.14 or 3.0, just 2.18.
> 
> It was most likely fixed by:
> https://github.com/qgis/QGIS/commit/abc0919 "Fix area calculation of
> compoundcurve rings if they contain a 2-vertex linestring"
> 
> Committed to 2.14 (with unit tests), I forward ported to 3.0, but it
> hasn't been applied to 2.18. I'll do this.
> 
> Nyall

  
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