Am 21.02.2014 15:41, schrieb Jonathan Moules:
Hi List,
Two issues,
First, I'm noticing that quite a few of the layers we have that are in
British National Grid aren't actually treated that way when I load them
into QGIS. This seems to be because they have a very slightly different
definition than the one QGIS has.
For example:
+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
+ellps=airy +towgs84=375,-111,431,0,0,0,0 +units=m +no_defs
+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
+ellps=airy +towgs84=446.448,-125.157,542.06,0.1502,0.247,0.8421,-20.4894
+units=m +no_defs
QGIS definition
+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000
+ellps=airy +towgs84=446.448,-125.157,542.06,0.15,0.247,0.842,-20.489
+units=m +no_defs
Three different definitions for the same thing.
Not really the same. The first uses a three-parameter datum shift which
is less accurate than the 7-paramrters used by the other ones.
Number 2 and three are almost identical.
So my question:
Is it possible to make QGIS recognise all the different definitions as one
single definition?
No, better not.
Greetings,
André Joost
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