Hi Mark, That's interesting - I'd not come up against custom formats before, so I'll take a look at that.
My main concern is that for shapefiles I'd quite like to create PRJ files (and equivalents for other formats where possible), in the interest of good practice, so that it's immediately clear what grid is being used, and so that the datasets can be overlaid regardless of co-ordinate system. Also, this is a massive engineering project (they've decided to invent their own grid system, in their infinite wisdom) which will be ongoing for the next few years, and will probably require numerous conversions, so I'm slightly concerned about (a) setting up a system that anyone can use; and (b) setting up a system that I can use without any bother... Anyway unfortunately the one thing it won't be is a one-off job!!! When you say you can't think of how to do it, does that mean you think it's impossible? Thanks again for your help, Roland. On 20/06/07, mark2atsafe <[EMAIL PROTECTED]> wrote:
Hi Roland, I can't think of how to do this off-hand, but it did occur to me that if you have the Scaler and Offsetter working you could set it all up as a Custom Format. I'm not totally sure how that works with multiple layers, but I think there's a good chance it would apply it to all (or at worst you could define all your layers in the custom format, which would be a pain, but a one-off job). Hope this is of use, Mark --- In [email protected] <fme%40yahoogroups.com>, "Roland Martin" < [EMAIL PROTECTED]> wrote: > > Hi, > > I've got a load of data that needs converting to a local grid that's based > on British National Grid. Up to now I've been doing it in a custom > transformer using a scaler and offsetter, but it would be quite handy if I > could set it up as a custom co-ordinate system, as some of the datasets have > large numbers of layers. Unfortunately the maths is a bit beyond me thus > far, so I was wondering if anyone could help. > > So here's British National Grid, for the uninitiated: > > COORDINATE_SYSTEM_DEF BritishNatGrid \ > DESC_NM "British National Grid (ORD SURV GB) (EPSG #27700)" \ > GROUP "EUROPE" \ > DT_NAME OSGB-7P \ > PROJ TM \ > UNIT METER \ > PARM1 -2.0 \ > ORG_LAT 49.0 \ > SCL_RED 0.9996012717 \ > X_OFF 400000.0 \ > Y_OFF -100000.0 \ > MAP_SCL 1.0 > > ... and the one I'm trying to set up is as follows: > > x = ( ( bngX - 537500 ) / 0.99983344 ) + 27500 > y = ( ( bngX - 185000 ) / 0.99983344 ) + 15000 > > ... so presumably I need to modify the SCL_RED; X_OFF and Y_OFF values. > > Can any local geniuses give me a hand with the numbers here? I've managed to > get it reasonably close, but it's a couple of metres off. > > Thanks, > Roland. >
