Hi Nyall (and list) A small projecto with UTM and GEO layers can be downloaded from dropbox:
https://www.dropbox.com/s/c4cfb48r5326vrk/Cajamarca.zip?dl=0 Attribute table has the correct area in AreaKm2 field (and in these unities). "AreaOTFoff" is the area given by field calculator when "On The Fly transformation" is deactivated. "AreaOTF_on" is the area with it activated. So: when I have a GEO layer, I can't calculate correct area directly in that layer: I've to reproject to UTM and deactivate automatic transformation of SRCs, to use field calculator expecting correct values. OS : Ubuntu 16.04 QGIS : 2.16.3 SRC settings: by default (ellipsoide WGS84 for measures) Thank you for your interest Carlos Cerdán 2016-10-14 15:14 GMT-05:00 Nyall Dawson <[email protected]>: > On 15 Oct 2016 12:51 AM, "Carlos Cerdán" <[email protected]> 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? > > Hi Carlos, > > Can you please share your file? Cut it down to just a few polygons and let > me know what area you expect to see. Email direct to myself. > > Thanks! > > Nyall > > > > > Regards from Peru > > > > Carlos > > > > > > > > 2016-10-12 18:06 GMT-05:00 Nyall Dawson <[email protected]>: > >> > >> On 12 Oct 2016 11:56 PM, "Carlos Cerdán" <[email protected]> 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 <[email protected]>: > >> >> > >> >> 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/ > general_tools.html#measuring > >> >> > >> >> 2016-10-12 14:07 GMT+02:00 Nicolas Cadieux < > [email protected]>: > >> >>> > >> >>> 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- > calculating-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 > >> >>> [email protected] > >> >>> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user > >> >>> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user > >> >> > >> >> > >> >> > >> >> _______________________________________________ > >> >> Qgis-user mailing list > >> >> [email protected] > >> >> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user > >> >> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user > >> > > >> > > >> > > >> > _______________________________________________ > >> > Qgis-user mailing list > >> > [email protected] > >> > List info: http://lists.osgeo.org/mailman/listinfo/qgis-user > >> > Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user > > > > > >
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