[Qgis-user] OnTheFly Reprojections

[Jonathan Moules]

Thanks for the responses. I think that's going to have to be the longer
term plan.

Jonathan



On 21 February 2014 18:46, Etienne Tourigny <etourigny.dev at gmail.com> wrote:

> 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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