Bug report #15982
Data not being saved to PostGIS database consistently
|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|
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.
#1 Updated by John Zielinski almost 6 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 almost 6 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):
I suspect it's because the shortest form was less than the maximum digits displayed.
#5 Updated by Giovanni Manghi over 3 years ago
- Status changed from Open to Closed
- Resolution set to end of life
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