Bug report #15982
Data not being saved to PostGIS database consistently
| Status: | Closed | ||
|---|---|---|---|
| Priority: | Normal | ||
| Assignee: | - | ||
| Category: | Data Provider/PostGIS | ||
| Affected QGIS version: | 2.18.0 | Regression?: | No |
| Operating System: | Easy fix?: | No | |
| Pull Request or Patch supplied: | No | Resolution: | end of life |
| Crashes QGIS or corrupts data: | No | Copied to github as #: | 23898 |
Description
I'm using QGIS Desktop with a PostGISdatabase. I've created a polygon with 4 points (A to D) and then another polygon inside it with 3 points. Those three points were then snapped to 3 of the points in the first polygon (A, C and D). The vertex editor shows this (I've changed the first column here to label the points):
1A -127.524251009317 51.4891731834931 1B -127.556950974351 51.445477703804 1C -127.563090533222 51.4681981465143 1D -127.572335727596 51.4754127899731 1A -127.524251009317 51.4891731834931
2A -127.524251009317 51.4891731834931 2D -127.572335727596 51.4754127899731 2C -127.563090533222 51.4681981465143 2A -127.524251009317 51.4891731834931
As you can see 1A = 2A, 1C = 2C and 1D = 2D. In my database however:
1A -127.52425100931688 51.489173183493094 1B -127.55695097435051 51.44547770380399 1C -127.5630905332221 51.46819814651429 1D -127.57233572759607 51.47541278997306 1E -127.52425100931688 51.489173183493094
2A -127.524251009317 51.4891731834931 2B -127.572335727596 51.4754127899731 2C -127.563090533222 51.4681981465143 2D -127.524251009317 51.4891731834931
The three common points are not the same! They round to the values shown in QGIS but cause random errors when I do ST_Contains on the polygons. Sometimes polygon 1 contains polygon 2 and sometimes it doesn't. The reason for the randomness is that by resnapping just one point and saving I get:
1A -127.52425100931701 51.48917318349311 1B -127.556950974351 51.44547770380399 1C -127.5630905332221 51.4681981465143 1D -127.57233572759607 51.47541278997306 1E -127.52425100931701 51.48917318349311
2A -127.524251009317 51.4891731834931 2B -127.57233572759606 51.475412789973056 2C -127.56309053322208 51.468198146514275 2D -127.524251009317 51.4891731834931
Totally different values as far as PostGISis concerned.
Just to be sure it's not PostGIS I tried this:
UPDATE shapes SET geog = ST_GeomFromEWKT('SRID=4326;MULTIPOLYGON(((-127.524251009317 51.4891731834931,-127.556950974351 51.445477703804,-127.563090533222 51.4681981465143,-127.572335727596 51.4754127899731,-127.524251009317 51.4891731834931)))') WHERE id = 1;
UPDATE shapes SET geog = ST_GeomFromEWKT('SRID=4326;MULTIPOLYGON(((-127.524251009317 51.4891731834931,-127.572335727596 51.4754127899731,-127.563090533222 51.4681981465143,-127.524251009317 51.4891731834931)))') WHERE id = 2;
And I always get the following in the database no matter how many times I do the UPDATEs:
1A -127.524251009317 51.4891731834931 1B -127.556950974351 51.445477703804 1C -127.563090533222 51.4681981465143 1D -127.572335727596 51.4754127899731 1A -127.524251009317 51.4891731834931 2A -127.524251009317 51.4891731834931 2D -127.572335727596 51.4754127899731 2C -127.563090533222 51.4681981465143 2A -127.524251009317 51.4891731834931
Note: The values in the database I've show were read by a C program that used a custom Postgres function to read the internal PostGIS GSERIALIZED binary data. This made sure nothing along the line mucked with the values (no conversions to or from WKT/WKB). The coordinates were printed using the very accurate and precise David M. Gay's floating-point conversion library.
History
#1
Updated by John Zielinski over 7 years ago
Just for reference, here's the range of doubles (float8) that 1A.x has in the tables above:
541afa4e -127.52425100931688 541afa4f -127.5242510093169 541afa50 -127.52425100931691 541afa51 -127.52425100931693 541afa52 -127.52425100931694 541afa53 -127.52425100931696 541afa54 -127.52425100931697 541afa55 -127.52425100931698 541afa56 -127.524251009317 541afa57 -127.52425100931701
#2
Updated by John Zielinski over 7 years ago
Found something new. Two snapped points again ended up being not the same but this time visible in the vertex editor (just the x value):
-90.237137558
-90.2371375579999I suspect it's because the shortest form was less than the maximum digits displayed.
#3
Updated by Giovanni Manghi almost 7 years ago
- Easy fix? set to No
- Regression? set to No
#4
Updated by Jürgen Fischer over 6 years ago
- Assignee deleted (
Jürgen Fischer)
#5
Updated by Giovanni Manghi about 5 years ago
- Status changed from Open to Closed
- Resolution set to end of life
End of life notice: QGIS 2.18 LTR
Source:
http://blog.qgis.org/2019/03/09/end-of-life-notice-qgis-2-18-ltr/
QGIS 3.4 has recently become our new Long Term Release (LTR) version. This is a major step in our history – a long term release version based on the massive updates, library upgrades and improvements that we carried out in the course of the 2.x to 3x upgrade cycle.
We strongly encourage all users who are currently using QGIS 2.18 LTR as their preferred QGIS release to migrate to QGIS 3.4. This new LTR version will receive regular bugfixes for at least one year. It also includes hundreds of new functions, usability improvements, bugfixes, and other goodies. See the relevant changelogs for a good sampling of all the new features that have gone into version 3.4
Most plugins have been either migrated or incorporated into the core QGIS code base.
We strongly discourage the continued use of QGIS 2.18 LTR as it is now officially unsupported, which means we’ll not provide any bug fix releases for it.
You should also note that we intend to close all bug tickets referring to the now obsolete LTR version. Original reporters will receive a notification of the ticket closure and are encouraged to check whether the issue persists in the new LTR, in which case they should reopen the ticket.
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