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I have the problem that when I create a new point (in a point layer) or a new line (in a line layer of course) and I save the changes to the layer (so NOT the project save) then QGIS rounds up the coordinates of the new element to six decimals. I can see that in the "identify results" window by clicking on "(Derived"). So as a result, I don't get the required position of the new element. The layers are DB tables that I received and I just open them in QGIS. I don't know the source of the layers. The CRS of the project is the same as the CRS of the layer. The thing is, if I create a new shapefile-layer myself (point for example), the new element remains in the wanted location even after saving layer changes. So it has something to do with the layer I received. But I don't know what that is. I am trying for 3 days to find a solution and can't seem to solve the problem. Does anyone have a hint for me?

Bevore saving the layer changes: bevore save

After saving the layer changes: after save

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  • What is the format of the layer that you have? Shape?
    – Nathan W
    Feb 19, 2013 at 9:34
  • That's the problem. I don't know. I access the layer from a network database (MSSQL/dbo) and can't see any extension of the file. I suspect it is not a shapefile. Heard these is data translated somehow in osm format. Unfortunately i can not find out more today about the source of the layer. Any idea?
    – Tudor
    Feb 19, 2013 at 9:43
  • Well I guess it's just a database layer.
    – Nathan W
    Feb 19, 2013 at 10:47
  • @Nathan W that sounds plausible. But still, why does QGIS round up?
    – Tudor
    Feb 19, 2013 at 11:09
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    If the geometries are stored in a database, database settings might limit the number of digits.
    – underdark ♦
    Feb 22, 2013 at 15:44

2 Answers 2

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This is a bug in QGIS. I've created a bug report here.

It relates to the MS SQL data provider using WKT by default to save and update records. The QgsGeometry::exportToWkt() method rounds coordinates to 6 decimal places. In more recent versions, this has been increased to 8, but it is still rounding.

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This is actually an issue with floating point calculation where in binary computers can't see recurring numbers and therefore can't round. It doesn't matter if you're in a billion dollar ArcGIS development environment or QGIS world, the issue is that you are in binary base2.

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