[Qgis-user] Mesaure tool Problem

[Bernhard Ströbl]

we use our local projection all our data is in, currently EPSG:31468, 
next year ETRS89 (EPSG:25832). No need to reproject data and we do not 
need Google maps for anything. Both projections are ok for small scale 
mapping and measure errors are below measure accuracy (I guess :).
If you want to use Google map layers as background you need to use the 
GoolgeMercator projection, though, but be aware that the Google 
background layer is not included in the prints (because it is not part 
of the QGIS project on which the server generates the print).

Bernhard

Am 19.09.2013 15:08, schrieb Martin Baloga:
> Thank you, Bernard.
>
> What about your portal of City of Jena, do you use GoogleMercator? Are your
> distances measured in the geoportal right?
>
>
> S pozdravom / Best regards / Salutanta
> Ing. Arch. Martin Baloga, PhD.
> www.jazzarchitecture.sk
> +421 903 314 492
>
>
> 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.
>
>
> -----Original Message-----
> From: Bernhard Ströbl [mailto:bernhard.stroebl at jena.de]
> Sent: Thursday, September 19, 2013 2:52 PM
> To: Martin Baloga
> Cc: qgis-user at lists.osgeo.org
> Subject: Re: Mesaure tool Problem
>
> 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
>>
>>
>> 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.
>>
>>
>>
>> -----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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-- 
Bernhard Ströbl
Anwendungsbetreuer GIS

Kommunale Immobilien Jena
Am Anger 26
07743 Jena

Tel.: 03641 49- 5190
E-Mail: bernhard.stroebl at jena.de
Internet: www.kij.de


Kommunale Immobilien Jena
Eigenbetrieb der Stadt Jena
Werkleiter: Dr. Götz Blankenburg


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