Bug report #9620
Measure line tool reports incorrect units
|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|
After loading OpenStreetMap layer with the Open Layers plugin the measurement tool malfunctions
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
#1 Updated by Giovanni Manghi about 6 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
that probably we have to close in favor of a new one to discuss on how to improve this controls/options.