[Qgis-developer] RE: [Qgis-user] Scale seems strange in
Giovanni Manghi
giovanni.manghi at gmail.com
Fri Nov 4 12:42:15 EDT 2011
Hi,
I can confirm that in my qgis-master on Ubuntu 11.10 the scale is going
crazy with epsg:3763 and others projected CRSs. Seems fine with WGS85.
Cheers
-- Giovanni --
On Fri, 2011-11-04 at 09:15 +0000, James Stott wrote:
> Thanks for the response and your explanation. It helped to cement what
> I already thought.
>
>
>
> My point is I think something has gone strange with EPSG 27700 in QGIS
> at the moment. It works fine on 1.7.1 and not on the OSGeo4W
> 1.8.0-120. It never used to set the units to degrees – it should be
> metres.
>
>
>
> I think that QGIS is getting the default units wrong for 27700. The
> coordinate system definition states that the units should be m.
>
>
>
> I am also reporting this behaviour on my windows computer at home
> (completely separate to the computers we have the issue on at work)
> and a computer using Ubuntu 11.10. And on a windows machine on
> (1.8.0-78) it works fine.
>
>
>
> I have also noticed a change in the behaviour of Save As... When
> exporting to MapInfo MIF. Previously QGIS was getting the export wrong
> and using BNG with WGS84, now it is exporting it to BNG with OSGB36
> (which is correct).
>
>
>
>
> 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: kidsmake6until2019 at gmail.com
> [mailto:kidsmake6until2019 at gmail.com] On Behalf Of Brad Nesom
> Sent: 02 November 2011 19:49
> To: James Stott
> Cc: Saber Razmjooei; qgis-user at lists.osgeo.org
> Subject: Re: [Qgis-user] Scale seems strange in
>
>
>
>
> so did you understand why?
>
>
> lat lon is not an equidistant coordinate system. It is an angular
> measure. The graticules merge closer togehter the further north they
> go.
>
>
> When you overlay data projected to ll onto a flat surface the lengths
> east west at the top are shorter than the lengths east west at the
> bottom.
>
>
> that is what is changing the scale because without zooming the scale
> of the objects would change by panning the map north and south.
>
>
> Nothng about the scale is changing except the distance measured
> across. No coordinate values.
>
>
> HTH
>
>
>
>
>
>
>
> On Wed, Nov 2, 2011 at 10:12 AM, James Stott
> <James.Stott at npaconsult.co.uk> wrote:
>
> If I use the arrow keys to pan north and south the scale changes. If I
> use them to pan left and right it doesn’t change.
>
>
>
>
> 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: kidsmake6until2019 at gmail.com
> [mailto:kidsmake6until2019 at gmail.com] On Behalf Of Brad Nesom
> Sent: 02 November 2011 15:00
> To: James Stott
> Cc: Saber Razmjooei; qgis-user at lists.osgeo.org
> Subject: Re: [Qgis-user] Scale seems strange in
>
>
>
>
> 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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