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<DIV><FONT face="Courier New">Thanks Nicholas,</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">If I’m understanding it correctly (and I
appologise if I’m not), te method you provide would allow me to elliminate any
of my vector grid cells which fall on land (or more precisely which have centres
that fall on land), which is useful. However, what I need to be able to do is to
separate each grid cell which lies along any stretches of coastline into two
separate irregular polygon features, one which falls entirely in the sea and one
which falls entirely on land. I can then delete the sections of all the grid
cells which fall on land. </FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">The process that I use for doing this is to use
the Union tool to create a combined data layer of my land polygons and my
polygon grid cells, and then use the ID field from the land polygon data layer
to select and delete the sections which overlap with the land polygons, leaving
me with a vector grid which is clipped exactly along the coastline, and has
partial grid cells for these coastal cells that only represent the sea parts of
them.</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">As I said, this approach used to work perfectly in
QGIS 2.2 and 2.4, but I can only get the Union tool to work intermittently in
QGIS 2.6, and when it doesn’t work, I get the Feature Geometry Not Imported (OGR
Error:) error message. </FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">At the moment, this is the one thing which is
stopping me being able to ditch ArcGIS and instead use QGIS as the basis for
teaching marine biologists to use GIS in their research using our standard
protocols for processing data, so any suggestions on what might be going wrong
with the Union tool, and how I might be able to deal with it, would be greatly
appreciated.</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">I would prefer to be able to use the Union tool in
my exercises, but if there is another way of doing it that will allow me to
split the coastal cells of my vector grid into irregular polygons that are
entirely land and entirely sea, then I would consider that.</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">Thanks for any further advice anyone can
offer.</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">All the best,</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">Colin</FONT></DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New"></FONT> </DIV>
<DIV><FONT face="Courier New">>>Hi, You can use the point sampling tool
plugin for that. Extract your grid centroid, use the new point layers with the
point >>sampling tools. You can also sample raster and vector values with
the tool. You can rejoin both layer later in a number of ways. >>If you
want to eliminate points, (or grid squares if both have been joined) you can use
a query. If you have millions features, >>this may be slow. In that case,
use the "split vector file" using a column. For more tools for your work, look
at the plugins for >>"stats". You will find a number of good plugins for
extracting statistics from vector or raster data. There are also many tools in
>>the " processing" tools. Send me a mail if you need more help. I Like
what you are doing... Nicolas Cadieux M.Sc. Les Entreprises >>Archéotec
inc. 8548, rue Saint-Denis Montréal H2P 2H2 Téléphone: 514.381.5112 Fax:
514.381.4995 Le 2014-12-05 09:37, "Colin D. >>MacLeod [via OSGeo.org] "
<</FONT><A style="WHITE-SPACE: pre"
href="http://lists.osgeo.org/mailman/listinfo/qgis-user"><FONT
face="Courier New">ml-node+s1560n5176645h56 at n6.nabble.com</FONT></A><FONT
face="Courier New">> a écrit : </FONT></DIV>
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