Nyall, in 2.14.6 I get incorrect areas in a layer with CRS 3857 but not with a layer CRS 26910(UTM 10N).
With the UTM layer I get different areas with OTR on and off, but the difference is small and I assume it is just due to the different ellipsoids. When calculating area in the field calculator with a layer whose CRS is 3857 I get the correct area in these cases: 1) OTR is turned off or 2)ellipsiod is set to None/planimetric. If the default ellipsoid for the project CRS is kept I get incorrect area values with 2 different project CRS': 3857 and 26910(UTM 10N). the difference in values is large and variable, for instance: correct vs incorrect 20243 sqm vs 612695 sqm 1333 sqm vs 721 sqm Andrew On Fri, Oct 14, 2016 at 7:51 AM, Carlos Cerdán <sig.up...@gmail.com> wrote: > Hi Nyall > > I'm afraid that 2.16 has still this issue. I've loaded an UTM-17 south > layer (my zone) and a Lat-long layer and: > > 1. SRC was seted in UTM > > 2. In UTM layer, if OTF SRC transformation is active, I get different area > than if it's deactivated. Correct value is the last one. > > 3. In Lat-long layer, if OTF SRC transformation is active, calculated area > is same as the wrong value of first layer. I can't get the correct value in > this layer, so I have to reproject into a new one and do step 2 (with OTF > deactivated). > > What about a general option to set the prefered SRC to calculate areas and > lengths with OTF active? > > Regards from Peru > > Carlos > > > > 2016-10-12 18:06 GMT-05:00 Nyall Dawson <nyall.daw...@gmail.com>: > >> On 12 Oct 2016 11:56 PM, "Carlos Cerdán" <sig.up...@gmail.com> wrote: >> > >> > AFAIK, It also is needed to turn off "on the fly SRC transformation" to >> get correct area values.... Or QGIS has fixed this point? >> >> Everything should be fixed in recent versions, and I very (VERY) much >> want to know if any issues are still encountered. >> >> Calculating area/length is a core task for a GIS and we need to make sure >> it's rock solid. (Which it should be since 2.16!) >> >> Nyall >> >> >> > >> > If you can't get correct area values, check out about it.... >> > >> > >> > 2016-10-12 7:40 GMT-05:00 DelazJ <del...@gmail.com>: >> >> >> >> Hi, >> >> To complete Nicolas answer, you should check what are the measurements >> options set in Project --> Project Properties --> General tab. >> >> See also http://docs.qgis.org/2.14/en/docs/user_manual/introduction/g >> eneral_tools.html#measuring >> >> >> >> 2016-10-12 14:07 GMT+02:00 Nicolas Cadieux < >> nicolas.cadi...@archeotec.ca>: >> >>> >> >>> Hi, >> >>> You may be calculating square degrees and not metres. It can depend >> on the crs depending on the tools you are using. >> >>> Nicolas >> >>> >> >>> Le 11 oct. 2016 à 08:54, Martina Schäfer [via OSGeo.org] <[hidden >> email]> a écrit : >> >>> >> >>>> I experienced some confusion with calculation of area using the >> field calculator in QGIS version 2.16.3. Since I'm using MapInfo >> Professional as well, I mainly use tab-files that I can open in both >> programmes, but occasionally I save as shapefile since this used to be the >> default in QGIS. >> >>>> >> >>>> When comparing files, I coincidently realized that there was a >> mismatch in calculated area for the shapefile and the tab-file for exactly >> the same polygons! I used the field calculator in the attribute table in >> both cases, but for the shapefile the resulting areas were almost doubled >> in area compared to the tab-file. Any idea why this is happening? >> >>>> >> >>>> I also realized similar differences when calculating area in a file >> where projection has been converted from SWEREF99TM (a Swedish national >> projection) to WGS84. There differences occurred in both the tab and >> shapefile compared to the area calculated for the same tab-file in MapInfo. >> Again I find this very confusing! >> >>>> >> >>>> I need to rely on the area-calculations thus I really hope someone >> here can explain to me what is happening! >> >>>> >> >>>> Thanks in advance, >> >>>> Martina >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> ________________________________ >> >>>> If you reply to this email, your message will be added to the >> discussion below: >> >>>> http://osgeo-org.1560.x6.nabble.com/inconsistenty-when-calcu >> lating-area-depending-on-file-type-or-projection-tp5290228.html >> >>>> To start a new topic under Quantum GIS - User, email [hidden email] >> >>>> To unsubscribe from Quantum GIS - User, click here. >> >>>> NAML >> >>> >> >>> >> >>> ________________________________ >> >>> View this message in context: Re: inconsistenty when calculating area >> depending on file type or projection? >> >>> Sent from the Quantum GIS - User mailing list archive at Nabble.com. >> >>> >> >>> _______________________________________________ >> >>> Qgis-user mailing list >> >>> Qgis-user@lists.osgeo.org >> >>> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user >> >>> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user >> >> >> >> >> >> >> >> _______________________________________________ >> >> Qgis-user mailing list >> >> Qgis-user@lists.osgeo.org >> >> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user >> >> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user >> > >> > >> > >> > _______________________________________________ >> > Qgis-user mailing list >> > Qgis-user@lists.osgeo.org >> > List info: http://lists.osgeo.org/mailman/listinfo/qgis-user >> > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user >> > > > _______________________________________________ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: http://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user >
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