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.
