Bug report #21965

Different length measures between QGIS 2.18 and QGIS 3.4

Added by Florian Hruby 7 months ago. Updated 7 months ago.

Status:Feedback
Priority:Normal
Assignee:-
Category:Field calculator
Affected QGIS version:3.4.6 Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:
Crashes QGIS or corrupts data:No Copied to github as #:29780

Description

I noticed that the "$length" command returns slightly different values in QGIS 2.18 and QGIS 3.4.6 As the values in QGIS 2.18 conincide with calculation made in ArcMap, I suppose an issue with QGIS 3.4.6

qgis_218_346.png - length_1: calculated in 3.4.6 (8.91 KB) Florian Hruby, 2019-04-30 08:23 PM

History

#1 Updated by Giovanni Manghi 7 months ago

  • Status changed from Open to Feedback

$ length > "The length calculated by this function respects both the current project's ellipsoid setting and distance unit settings. For example, if an ellipsoid has been set for the project then the calculated length will be ellipsoidal, and if no ellipsoid is set then the calculated length will be planimetric"

are you sure you are using the same project properties regarding the ellipsoid being used?

#2 Updated by Florian Hruby 7 months ago

I´m pretty sure, but maybe you could check back on your side with both QGIS 3.4 and 2.18? the shape I used can be downloaded here:
https://drive.google.com/file/d/1azK-l4w2hbW1XJicmIQkyHXDl3rnikqx/view?usp=sharing

#3 Updated by Giovanni Manghi 7 months ago

Florian Hruby wrote:

I´m pretty sure, but maybe you could check back on your side with both QGIS 3.4 and 2.18? the shape I used can be downloaded here:
https://drive.google.com/file/d/1azK-l4w2hbW1XJicmIQkyHXDl3rnikqx/view?usp=sharing

nope, I don't have a 2.18 installation at the moment (not on the pc I'll have at hand in the upcoming days).

#4 Updated by Florian Hruby 7 months ago

Seems that the $length command gives the planar distance in QGIS 2.18, but the geodesic distance in QGIS 3.4:
https://gis.stackexchange.com/questions/321176/different-length-measures-in-qgis-vs-arcmap

Not sure if this is intentional?

#5 Updated by Giovanni Manghi 7 months ago

Not sure if this is intentional?

there have been changes, and they were by design.

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