[Qgis-user] Problems with Union tool in QGIS 2.6

[Colin D. MacLeod]

Hi All,

I have been trying to translate a series of practical exercises to teach marine biologists from ArcGIS into QGIS to help promote use QGIS in marine biology as an alternative to commercial GIS sofftware.  However, I have run into a problem with one particular step in my standard training exercises. 

This step involves creating a vector grid with the vector grid tool, and then using the union tool to divide the vector grid cells into sections which are on land and on water, so the land portions can be removed (leaving just the portions which are in the sea – this allows for the calculation of the area of each vector grid cell which is covered in water and use it to correct for various biases this can introduce in analyses).

When working with QGIS 2.2 and 2.4, this process worked more or less perfectly, but in 2.6, I am having a intermittent problem where it will work on some occasions but not on others, using what should be more or less identical data layers and identical settings. When it doesn’t work, the Union tool hangs at a specific percentage (in this case 23%), and there is an error messsage which says: Feature Geometry Not Imported (OGR Error:).

I don’t know if it makes any difference, but I am using a user-defined coordinate reference sytem that is based on a transverse mercator projecton fr both the project and the input data layers for the union tool (this seemed to cause some problems in earlier versoins of QGIS, but work arounds were possible).

Can anyone offer advice as to what might be going on here and how to get round this issue? I can provide sample data layers on request.

The system which this problem is occurring on is a laptop running Windows 8.1 and QGIS 2.6.

I am keen to try to find some sort of solution to this as this is a standard process for marine biologists, and being unable to do it would limit the ability to work with QGIS as an alternative to commercial GiS software.

Thanks for any advice which can be provided.

All the best,

Colin

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