[Qgis-user] Mesaure tool Problem

[Bernhard Ströbl]

Hi Martin,

I further looked into this problem. As I indicated before the measure 
tool is pure OpenLayers. Read the text underneath the example [1] for 
further explanation (the map is somehow not working in the example). 
Obviously QGIS desktop always uses "geodesic measures" whereas QWC never 
does. I filed a ticket [2].
BTW the problem comes from the GoogleMercator projection as the Mercator 
projection in general is known to only preserve angle while the area and 
length errors increase towards the poles.

Bernhard

[1] http://www.openlayers.org/dev/examples/measure.html
[2] http://hub.qgis.org/issues/8630

Am 19.09.2013 12:00, schrieb Martin Baloga:
> Hi, Bernard,
>
> No, in desktop I have 900913 the project CRS, when I measure any feature,
> the result is 90 m. (The same as in ArcMap with S-JTSK CRS). When I open the
> project with CRS set to 900913, I got 130 m.  for the same feature. When I
> open the WMS in ArcMap or any other GIS viewer I got again 90 m in 900913.
>
> The same, with the same values, happens when using 4326.
>
> Simply in QWC for some reason the measure is different. I would realy
> appreciate if the measures are correct. I am prepraring QWC for a
> municipality and the difference between parcel area in attribute and measure
> tool is quite confusing...
>
> S pozdravom / Best regards / Salutanta
> Ing. Arch. Martin Baloga, PhD.
> www.jazzarchitecture.sk
> +421 903 314 492
>
>
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> -----Original Message-----
> From: Bernhard Ströbl [mailto:bernhard.stroebl at jena.de]
> Sent: Thursday, September 19, 2013 11:28 AM
> To: qgis-user at lists.osgeo.org
> Cc: Martin Baloga
> Subject: Re: Mesaure tool Problem
>
> hi,
>
> so if you measure in QGIS desktop with project CRS set to 4326 you measure
> 90m and in QWC with CRS 4326 you measure 130m for the same feature?
> If I open a 4326-project in desktop my measure results are output in degrees
> (can I change that somehow?), so I cannot compare to the QWC output of the
> same project which is in metres. If you use a different projection in
> desktop then your measurements may - of course - be different.
> Measurement in QWC is handled using the OpenLayers' measure control [1]
>
> Bernhard
>
> [1]
> http://dev.openlayers.org/releases/OpenLayers-2.13.1/doc/apidocs/files/OpenL
> ayers/Control/Measure-js.html
>
> Am 19.09.2013 10:50, schrieb Martin Baloga:
>> Dear Bernard,
>>
>> e.g. by meauring length of cca 90 m in QGIS, the length measured in
>> web client is approx. 130 m. The size of the are is approx. Twice the
>> size. I guess maybe the units there are somewhere not properly set.
>> But in options.js and webinit.js are only m.
>>
>> If you are interrested, i can send you wms link and address of the
>> webclient. Thanx.
>>
>>
>> S pozdravom / Best regards / Salutanta Ing. Arch. Martin Baloga, PhD.
>>
>> Pred vytlačením tohto e-mailu myslite na životné prostredie.
>> Please consider your environmental responsibility before printing this
>> e-mail.
>> Mi petas vin pripensu pri via respondeco por la cxirkauxajxo antauxe
>> elpreso de tiu-cxi mesagxo.
>>
>>
>>
>>
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