Re: [GRASS-dev] v.proj: line densification added for reprojection error minimization

2014-12-14 Thread Helmut Kudrnovsky 
>The result (see screenshot, maybe an extreme example but yet helpful
>to show the improvement) shows how nicely the projection is performed
>now (green color is new output).
>Please benchmark this with other GIS... 

attached, done with a GIS from redmont


 



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Helmut
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Re: [GRASS-dev] v.proj: line densification added for reprojection error minimization

2014-12-14 Thread Helmut Kudrnovsky 
Helmut Kudrnovsky wrote
>>The result (see screenshot, maybe an extreme example but yet helpful
>>to show the improvement) shows how nicely the projection is performed
>>now (green color is new output).
>>Please benchmark this with other GIS... 
> 
> attached, done with a GIS from redmont

to be fair, there is a tool there for densifying lines and polygons; applied
this first, vector reprojecting also works correctly there.


 



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Re: [GRASS-dev] v.proj: line densification added for reprojection error minimization

2014-12-14 Thread Markus Neteler 
On Sun, Dec 14, 2014 at 6:14 PM, Helmut Kudrnovsky  wrote:
> Helmut Kudrnovsky wrote
>>>The result (see screenshot, maybe an extreme example but yet helpful
>>>to show the improvement) shows how nicely the projection is performed
>>>now (green color is new output).

BTW; now posted also here:
http://courses.neteler.org/grass-gis-7-vector-data-reprojection-automated-vertex-densification/


>>>Please benchmark this with other GIS...
>>
>> attached, done with a GIS from redmont
>
> to be fair, there is a tool there for densifying lines and polygons; applied
> this first, vector reprojecting also works correctly there.
>
> 

Good - but is that the default or requires extra tricks/knowledge?

And how about QGIS? Because ogr2ogr delivers only the trapezoid with
default settings.

Markus
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Re: [GRASS-dev] v.proj: line densification added for reprojection error minimization

2014-12-14 Thread Helmut Kudrnovsky 
>>

>
>Good - but is that the default or requires extra tricks/knowledge? 

2 steps with 2 different tools are needed: (1) densify polygon line, (2)
reproject to new SRS; and of course the knowledge that large polygons may
need some densifying.



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Re: [GRASS-dev] v.proj: line densification added for reprojection error minimization

2014-12-14 Thread Helmut Kudrnovsky 
> And how about QGIS?

the same, 2 steps are needed: (1) densify data, (2) reproject vector



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Re: [GRASS-dev] v.proj: line densification added for reprojection error minimization

2014-12-14 Thread Markus Metz 
On Sun, Dec 14, 2014 at 7:34 PM, Helmut Kudrnovsky  wrote:
>> And how about QGIS?
>
> the same, 2 steps are needed: (1) densify data, (2) reproject vector

for non-topological polygons, 3 steps are needed:
1) densify
2) snap
3) reproject

snapping is needed to avoid small overlapping areas and small gaps
between polygons. For topological areas composed of boundaries, this
is not an issue.

Markus M
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