[Qgis-developer] Snapping tolerance

Marco Hugentobler marco.hugentobler at sourcepole.ch
Mon Dec 15 00:07:50 PST 2014

Hi Denis

 >Regarding Marco’s use case, using the 50cm limit should be equivalent 
in map units, no?

The map units can be degrees and the layer units meters. Morover, the 
distortion is not equal in x- and y- direction. So converting the 50cm 
to degrees will be a different number depending where you are on the map 
and in which direction. The same holds for conversions between meter 
systems (e.g. google mercator <-> swiss grid). So the only more or less 
accurate thing is to use layer units.


On 14.12.2014 14:20, Rouzaud Denis wrote:
> Hi,
> I would say +1 for map units.
> Regarding Marco’s use case, using the 50cm limit should be equivalent 
> in map units, no?
> From my point of view, the settings of snapping are far too advanced 
> for 95% of the usage. Let’s not make them even more complicated, just 
> for a very specific use case.
> My 2 ct.
> Denis
>> On 13 Dec 2014, at 07:02, Martin Dobias <wonder.sk at gmail.com 
>> <mailto:wonder.sk at gmail.com>> wrote:
>> Hi
>> Recently I have been working on some snapping improvements (more 
>> about that later) and I have found one slightly surprising thing 
>> about the configuration of tolerances: if the tolerance unit is set 
>> to "map units", it actually means "layer units" - i.e. units in 
>> layer's CRS and not in project's CRS. Recently there was even a bug 
>> report filed for that: https://hub.qgis.org/issues/11634
>> I would like to change the behavior so that the "map units" in 
>> snapping config dialog would mean units in project's CRS. Would there 
>> be any objections?
>> Alternatively we could just rename "map units" to "layer units" to 
>> make it less surprising (and eventually add a third option to use 
>> project's units).
>> Cheers
>> Martin
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Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee

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