[Qgis-user] OnTheFly Reprojections

[Etienne Tourigny]

In this case you a probably better of making copies of the files with all
the same CRS.


On Fri, Feb 21, 2014 at 11:41 AM, Jonathan Moules <
jonathanmoules at warwickshire.gov.uk> wrote:

> 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.
> This becomes a problem because On The Fly reprojection (which I've now
> been forced to disable permanently) is super slow. Even a simple polygon
> layer with a few dozen features on top of a WMS creates a very noticeable
> (several seconds) lag.
>
> So my question:
> Is it possible to make QGIS recognise all the different definitions as one
> single definition?
>
> Using a Master build from a couple of months ago.
>
> Thanks,
> Jonathan
>
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