Bug report #9620

Measure line tool reports incorrect units

Added by muscatelle - almost 7 years ago. Updated almost 7 years ago.

Status:Closed
Priority:Normal
Assignee:-
Category:Browser
Affected QGIS version:2.0.1 Regression?:No
Operating System:Ubuntu Easy fix?:No
Pull Request or Patch supplied:No Resolution:duplicate
Crashes QGIS or corrupts data:No Copied to github as #:18194

Description

After loading OpenStreetMap layer with the Open Layers plugin the measurement tool malfunctions

To reproduce:
1. Create a QGIS project with my local CRS : EPSG:3107 - GDA94 / SA Lambert
2. Load the test file attached containing 1 line feature only - length ~ 620m confirmed correct by physical measurement and by using the field calculator $length function
3. Measurement tool returns a length of ~ 620m
4. Load OpenLayers plugin - OpenStreeMap. CRS is reset to EPGS: 3857 WGS 84 / Pseudo Mercator
5. Measurement tool now returns a length of ~ 760m - distorted value also applies to area tool calculations and the grid decorator

"Tomas writing on StackExchange": http://gis.stackexchange.com/questions/66521/buffer-in-qgis-r-is-650-670-m-wide-instead-of-500-m/66592#66592 believes the units displayed are CRS units rather than metres

Test.shp (188 Bytes) muscatelle -, 2014-02-22 03:26 PM

Test.prj (439 Bytes) muscatelle -, 2014-02-22 03:26 PM

Test.shx (108 Bytes) muscatelle -, 2014-02-22 03:26 PM

Test.qpj (703 Bytes) muscatelle -, 2014-02-22 03:26 PM

Test.dbf (230 Bytes) muscatelle -, 2014-02-22 03:26 PM

History

#1 Updated by Giovanni Manghi almost 7 years ago

  • Resolution set to duplicate
  • Status changed from Open to Closed

In qgis 2.0.1 there was an issue that reported bogus area/length values when reprojection was ON.

This is fixed in qgis 2.2 but anyway there is a difference compared to qgis 1.8: in qgis 1.8 even with OTFR on the measurements/computation where always made on the plane. In QGIS 2.* it depends on what ellipsoid is configured at a project level (default is WGS84). So now with OTFR on and project is in epsg 3857 your line measures 621.09 meters, but you can always set the ellipsoid the "planimetric/none" and then still get 620.34 meters as length, even with OTFR on.

Technically now there is no issue, but it can be confusing for users. There is already a ticket about this issue

#9060

that probably we have to close in favor of a new one to discuss on how to improve this controls/options.

#2 Updated by muscatelle - almost 7 years ago

Thanks Giovanni - learnt a lot from your response
Tony

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