[Qgis-user] Scale seems strange in

Brad Nesom gisbradokla at live.com
Wed Nov 2 08:00:17 PDT 2011


I am thinking rather than that it is just the fact that when you use
degrees, moving in the map would give you a different scale.
Because every time you move north or south you have changed the length of
the x distance.
If you pan left and right (very carefully) do you see the scale not change?



On Wed, Nov 2, 2011 at 9:02 AM, James Stott <James.Stott at npaconsult.co.uk>wrote:

> Could this just be a windows thing then? I tried an older version of
> qgis-dev (1.8.0-78) on a different windows machine in the office and there
> are no problems. Metres should be the default setting for 27700 shouldn't
> it not degrees?
>
>
> James Stott BSc (Hons) MSc | Senior Professional
> Nicholas Pearson Associates | 30 Brock Street | Bath | BA1 2LN
> T: 01225 445548 | M: -
> http://www.npaconsult.co.uk/
>
> -----Original Message-----
> From: Saber Razmjooei [mailto:razmjooeis at faunalia.co.uk]
> Sent: 02 November 2011 10:48
> To: James Stott
> Cc: qgis-user at lists.osgeo.org
> Subject: RE: [Qgis-user] Scale seems strange in
>
> James
>
> I am using QGIS-Trunk under ubuntu 10.04. The canvas projection is set
> to 27700 and Layer unit to metre.
>
> The scale seems to be fine and not affected by panning.
>
> Cheers
> Saber
>
> On Wed, 2011-11-02 at 10:43 +0000, James Stott wrote:
> > An update:
> >
> >
> >
> > This is also happening on a colleague’s machine. I have reverted back
> > to the previous OSGeo4W nightly and that doesn’t fix the problem.
> > Uninstalling and reinstalling doesn’t work.
> >
> >
> >
> > In 1.7, if I open up this certain dataset of viewpoint locations, it
> > opens with a scale of 1:53478. In 1.8 if I load the dataset it opens
> > at a scale of 1:5325654358. If I use the pan tool and just click on
> > the map the scale changes to 1:631588609, then 1:2918610855, then
> > 1:2934133484 and so on. Distance measures seem unaffected. It seems to
> > be being caused by the units of the project being set to degrees. I
> > have saved a project and the units are set to degrees. If I open an
> > old project up it opens at the correct scale. In my old project files
> > it is set to metres. (see examples below). It seems I have to make
> > sure Enable on the fly projection is unticked in the project
> > properties, and then manually set the Layer units to metres in the
> > general tab.
> >
> >
> >
> > I was also having problems a while ago with exporting to MapInfo but I
> > have just tried this and it works. See links below for details. It is
> > including the 79 not the 104 now.
> >
> >
> >
> >
> http://gis.stackexchange.com/questions/14350/qgis-and-mapinfo-projections-epsg-27700-british-national-grid
> >
> > http://hub.qgis.org/issues/4271
> >
> >
> >
> > New project:
> >
> >
> >
> > <mapcanvas>
> >
> >         <units>degrees</units>
> >
> >         <extent>
> >
> >             <xmin>384571.226869</xmin>
> >
> >             <ymin>78401.536498</ymin>
> >
> >             <xmax>408875.829430</xmax>
> >
> >             <ymax>92579.221325</ymax>
> >
> >         </extent>
> >
> >         <projections>0</projections>
> >
> >         <destinationsrs>
> >
> >             <spatialrefsys>
> >
> >                 <proj4>+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717
> > +x_0=400000 +y_0=-100000 +ellps=airy
> > +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +units=m
> > +no_defs</proj4>
> >
> >                 <srsid>2437</srsid>
> >
> >                 <srid>27700</srid>
> >
> >                 <authid>EPSG:27700</authid>
> >
> >                 <description>OSGB 1936 / British National
> > Grid</description>
> >
> >                 <projectionacronym>tmerc</projectionacronym>
> >
> >                 <ellipsoidacronym>airy</ellipsoidacronym>
> >
> >                 <geographicflag>false</geographicflag>
> >
> >             </spatialrefsys>
> >
> >         </destinationsrs>
> >
> >     </mapcanvas>
> >
> >
> >
> > Old project:
> >
> >
> >
> > <mapcanvas>
> >
> >         <units>meters</units>
> >
> >         <extent>
> >
> >             <xmin>400790.090563</xmin>
> >
> >             <ymin>86512.592259</ymin>
> >
> >             <xmax>401731.465923</xmax>
> >
> >             <ymax>87217.568425</ymax>
> >
> >         </extent>
> >
> >         <projections>0</projections>
> >
> >         <destinationsrs>
> >
> >             <spatialrefsys>
> >
> >                 <proj4>+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717
> > +x_0=400000 +y_0=-100000 +ellps=airy
> > +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489 +units=m
> > +no_defs</proj4>
> >
> >                 <srsid>2437</srsid>
> >
> >                 <srid>27700</srid>
> >
> >                 <authid>EPSG:27700</authid>
> >
> >                 <description>OSGB 1936 / British National
> > Grid</description>
> >
> >                 <projectionacronym>tmerc</projectionacronym>
> >
> >                 <ellipsoidacronym>airy</ellipsoidacronym>
> >
> >                 <geographicflag>false</geographicflag>
> >
> >             </spatialrefsys>
> >
> >         </destinationsrs>
> >
> >     </mapcanvas>
> >
> >
> >
> >
> >
> >
> >
> >
> > James Stott BSc (Hons) MSc | Senior Professional
> > Nicholas Pearson Associates | 30 Brock Street | Bath | BA1 2LN
> > T: 01225 445548 | M: -
> > www.npaconsult.co.uk
> >
> >
> >
> > From: qgis-user-bounces at lists.osgeo.org
> > [mailto:qgis-user-bounces at lists.osgeo.org] On Behalf Of James Stott
> > Sent: 01 November 2011 09:15
> > To: qgis-user at lists.osgeo.org
> > Subject: [Qgis-user] Scale seems strange in
> >
> >
> >
> >
> > Hi all,
> >
> >
> >
> > I am having problems with scales on v1.8 (7297b23) from OSGeo4W.
> >
> >
> >
> > If I open an existing project everything is fine.
> >
> >
> >
> > If I open data in a fresh QGIS session it is reporting strange scales.
> > It doesn’t matter what source the data is. For example, I open a
> > dataset and it reports 1:784735546. It seems to report correct
> > distances. If I pan the scale changes.
> >
> >
> >
> > I am using EPSG 27700 (British National Grid).
> >
> >
> >
> > Does anyone have any idea what can be causing this?
> >
> >
> >
> > James
> >
> > James Stott BSc (Hons) MSc | Senior Professional
> > Nicholas Pearson Associates | 30 Brock Street | Bath | BA1 2LN
> > T: 01225 445548 | M: -
> > www.npaconsult.co.uk
> >
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