GBconv.opo   A module for Psion Series 5 and Geofox OPL programmers.

GBconv is a simple module which can be used to convert an UK National
Grid Reference into Latitude and Longitude, and vice-versa. It is
designed for use by OPL programmers.

To use it, simply LOADM the module into your program. You can then
use 3 procedures within the module to do the conversions:

 Ngr2LL:(ngr$,1)  is used to convert the NGR to degrees of latitude
 Ngr2LL:(ngr$,2)  is used to convert the NGR to degrees of longitude
 LL2Ngr$:(north,east)  will convert degrees north and east to an NGR

The module understands the NGR as used for England, Wales and Scotland,
also the Channel Islands (WA and WV) and Northern Ireland (C,D,G,H & J).
An NGR should be entered like: SP612045 or J470379.
Latitude and Longitude should be entered as degrees (decimal) like 51.2345
with south and west as negative, north and east as positive.

There is little error checking, so make sure your programs use the correct
format. The code which distinguishes where in the UK a given Lat and Lon 
are is very simplw, and I think it works! If a location in Northern 
Ireland gets given a mainland NGR please let me know the details!

This module was written for use by OPL programmers, who may use it and
distribute it free of charge. I make no guarantee to accuracy, but you can
easily check it out with an OS map.

Use the module entirely at your own risk. I accept no claims for damage to
your Psion or Geofox in any way whatsoever. The module was written out of
academic interest, it was not intended for hikers, explorers, or anyone
who might use it to find their war to safety.

The code within was written by Roger Muggleton and Roger Blakeway, for an
entirely different purpose! No doubt the maths is not original. If anything
goes wrong, please contact Roger Muggleton.   Email:  hzk@cix.co.uk

Demo code:

PROC ngr_latlon:
	LOCAL e,n,ngr$(8)
	FONT 268435958,1
	LOADM "GBconv.opo"
	ngr$="SW577456"
	PRINT ngr$
	n=Ngr2LL:(ngr$,1)
	e=Ngr2LL:(ngr$,2)
	PRINT "N",n
	PRINT "E",e
	ngr$=LL2ngr$:(n,e)
	PRINT ngr$
	GET
ENDP