Bug report #17151
wrong vector line length calculation by $length in attribute table calculator
| Status: | Closed | ||
|---|---|---|---|
| Priority: | High | ||
| Assignee: | - | ||
| Category: | Attribute table | ||
| Affected QGIS version: | 2.18.12 | Regression?: | No |
| Operating System: | windows 10 | Easy fix?: | Yes |
| Pull Request or Patch supplied: | No | Resolution: | fixed/implemented |
| Crashes QGIS or corrupts data: | No | Copied to github as #: | 25050 |
Description
attached a line vector shape file in EPSG:31287 (https://epsg.io/31287)
vector line length calculation seems to be wrong in QGIS 2.18.12
comparison between: QGIS 2.18.12, GRASS 7.3svn and QGIS-Version 2.99.0-Master QGIS-Codeversion ba9cb873ae
v.db.select map=test_vector_length@vlengthtest cat|id|qvlength|qvlength3|vlengthgrass 1||31.6929908772|31683.5186360268|31683.518636 2||128.842829285|128802.141660603|128802.141661 3||187.2653676151|187203.580023903|187203.580024 4||20.5063076544|20500.6624186491|20500.662419 5||56.5505940728|56535.5429605752|56535.542961 6||98.8004239584|98775.9189262182|98775.918926
qvlength => calculated by QGIS 2.18.12
qvlength3 => calculated by QGIS-Version 2.99.0-Master
vlengthgrass => calculated by GRASS 7.3.svn
line length is in meters.
qvlength3 and vlengthgrass are the same, but regarding qvlength calculated by 2.18.12 seems to wrong.
attached is the related shapefile and a spatialite db exported by GRASS, both with the length values in the attribute table.
tested with:
----
QGIS version
2.18.12
QGIS code revision
a6c461b
Compiled against Qt
4.8.5
Running against Qt
4.8.5
Compiled against GDAL/OGR
2.2.1
Running against GDAL/OGR
2.2.1
Compiled against GEOS
3.5.0-CAPI-1.9.0
Running against GEOS
3.5.0-CAPI-1.9.0 r4084
PostgreSQL Client Version
9.2.4
SpatiaLite Version
4.3.0
QWT Version
5.2.3
PROJ.4 Version
493
QScintilla2 Version
2.7.2
History
#1
Updated by Helmut Kudrnovsky almost 7 years ago
Helmut Kudrnovsky wrote:
attached a line vector shape file in EPSG:31287 (https://epsg.io/31287)
vector line length calculation seems to be wrong in QGIS 2.18.12
it seems that the decimal point is shifted.
#2
Updated by Helmut Kudrnovsky almost 7 years ago
- File vlength_epsg3035.zip added
Helmut Kudrnovsky wrote:
attached a line vector shape file in EPSG:31287 (https://epsg.io/31287)
vector line length calculation seems to be wrong in QGIS 2.18.12
now tested with another projection (EPSG:3035) - test shapefile attached.
the line length are for test case from ~10m up to ~1254830m
vlength3 vlength2 11.9809053481 0.0119809053 20.5154479097 0.0205154479 34.1924131816 0.0341924132 48.4426040881 0.0484426041 84.0983546768 0.0840983547 168.8711406481 0.1688711406 269.9793624986 0.2699793625 329.6264100979 0.3296264101 422.1590048316 0.4221590048 1260.8220223604 1.2608220224 2997.1665069434 2.9971665069 5805.2376357774 5.8052376358 29350.800049287 29.3508000493 111646.269300223 111.6462693002 207864.02027185 207.8640202719 303161.374344716 303.1613743447 790590.141646461 790.5901416465 1254830.64894956 1254.8306489496
vlength2 calculated by QGIS 2.18.12
vlength3 calculated by QGIS QGIS-Version 2.99.0-Master
also in this projection there seems to be an unwanted shift of the decimal point.
#3
Updated by Giovanni Manghi almost 7 years ago
- Status changed from Open to Feedback
Just tried on both Linux and Windows 7 with 2.18.12 and I get the right values.
#4
Updated by Helmut Kudrnovsky almost 7 years ago
- File testline_epsg31254.zip added
Giovanni Manghi wrote:
Just tried on both Linux and Windows 7 with 2.18.12 and I get the right values.
thanks for testing.
in OSGeo4W there is now QGIS 2.18.13 available.
QGIS version 2.18.13 QGIS code revision 8cba0bb9eb Compiled against Qt 4.8.5 Running against Qt 4.8.5 Compiled against GDAL/OGR 2.2.1 Running against GDAL/OGR 2.2.1 Compiled against GEOS 3.5.0-CAPI-1.9.0 Running against GEOS 3.5.0-CAPI-1.9.0 r4084 PostgreSQL Client Version 9.2.4 SpatiaLite Version 4.3.0 QWT Version 5.2.3 PROJ.4 Version 493 QScintilla2 Version 2.7.2
tested it with another vector shape in EPSG 31254 and compared it to QGIS 2.99.:
vlenqgs213 vlengqgs3 7.4098756 7409.9628946 23.7302064 23730.4588719 19.5467015 19546.9312967 32.6276445 32627.8490494 2.3586266 2358.6796179 0.8076811 807.708901 7.6789837 7679.2103411 3.2085795 3208.6738047 38.5676211 38568.1000222 1.0096307 1009.6361262 0.364028 364.0294823 0.5436955 543.7056935 14.0659768 14066.3523728 10.7428602 10743.0602009 11.028371 11028.4584316
still the issue. very strange.
any idea what's going on? any idea what to test?
#5
Updated by Nyall Dawson almost 7 years ago
Check your project distance unit setting - I suspect this is affecting the result.
#6
Updated by Helmut Kudrnovsky almost 7 years ago
Nyall Dawson wrote:
Check your project distance unit setting - I suspect this is affecting the result.
my workflow is:
- start qgis 2.18.13
- load shapefile in EPSG:31254
- check in project properties: Selected CRS: MGI / Austria GK West (+proj=tmerc +lat_0=0 +lon_0=10.33333333333333 +k=1 +x_0=0 +y_0=-5000000 +ellps=bessel +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 +units=m +no_defs)
- open attribute table to edit
- add Decimal number column
- calculate length by $length in the new column
where do I check project distance unit settings elsewhere than in the project properties?
#7
Updated by Helmut Kudrnovsky almost 7 years ago
Helmut Kudrnovsky wrote:
Nyall Dawson wrote:
Check your project distance unit setting - I suspect this is affecting the result.
my workflow is:
- start qgis 2.18.13
- load shapefile in EPSG:31254
- check in project properties: Selected CRS: MGI / Austria GK West (+proj=tmerc +lat_0=0 +lon_0=10.33333333333333 +k=1 +x_0=0 +y_0=-5000000 +ellps=bessel +towgs84=577.326,90.129,463.919,5.137,1.474,5.297,2.4232 +units=m +no_defs)
- open attribute table to edit
- add Decimal number column
- calculate length by $length in the new column
where do I check project distance unit settings elsewhere than in the project properties?
ok I've found it: something has changed in Settings -> Options -> MapTools -> Measure tool -> preferred distance units from meters to kilometers.
changing back to meters, calculations are ok.
thanks to Werner to help identifying the issue.
closing ticket.
though from a user point of view, I wouldn't assume, that I change in the manual measuring tool by going over Configuration the whole behaviour of length calculation.
#8
Updated by Werner Macho almost 7 years ago
- Resolution set to fixed/implemented
- Status changed from Feedback to Closed
- Crashes QGIS or corrupts data changed from Yes to No
- Regression? changed from Yes to No
- Easy fix? changed from No to Yes
Problem solved by choosing default Settings in "Project Properties" AND "Settings -> Options -> Map Tools -> Measure Tool"