MapForums

Hello,

Does anyone know EXACTLY what format MapPoint wants when entering a UK OS grid reference (in importing data)???

I know it has to be a single string like "205988 561299".
But it seems to want leading zeroes if there are less digits? e.g. "089315 013360"

And if in Northern Scotland just add the "1"? e.g. "440530 1110105"

I'm trying to figure out a format that I can tell Excel to use that will import but I always end up massaging the numbers by hand.

Thanks,
-random

I doubt it wants leading zeros for padding. Any padding zeros should be at the end of each direction - that is pretty much defined by the OSGR spec.

If you look at the OS Grid dialog box text, it says to enter a 8 character GR with letters (eg. TQ 1232 1232) or a 12-digit GR (eg. 054455 025889).

The first is a standard 8-figure grid reference. We used to use them to that accuracy (10m) for geological mapping.
The first two letters define the 100km square. The other two numbers are effectively cartesian coords in the square.
At school we used 6 and 4 figure GRs, but the least significant digits are the ones that are dropped off. (eg. 1km resol: TQ 12 12 ).

The 12-digit uses a digit prefix for each direction, instead of the two letters.
(ie. the above example is in the far SW 100km grid square).
It also has an extra level of preceision, bringing it to 1m resolution.


Richard

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Hi Richard,

I'm mapping things to 1m accuracy across the entire GB.

MapPoint definately wants numbers padded to a certain number of digits per co-ord, but padding at the r.h. end would multiply the co-ord up & move it I think. And not all places can be defined to 1m in 12 digits - i.e. Northern Scotland. So I'm still not sure what MapPoint is expecting.

Have you ever seen a definitive statement of what MapPoint expects?

-Random

Forget MapPoint for a moment...

OS Grid References always list the most significant digits.
So, SH75 is a 10km x 10km square in North Wales.
SH 7453 is a 1km square within that 10km square (somewhere near the village of Dolwyddelan iirc! )
SH 742531 is 100m square within that 1km square
SH 74215312 is a 10m square within that 100m square
SH 7421053128 is a 1m square within that 10m square.

(some electronic OS maps replace the letters with numbers that are prefixed to the two ordinates)

Do you see why truncation of a coordinate must be at the least significant end (right), and not the most significant end (left)?

If the (left) digits were removed, then you don't know which 10km square the coord is in. Whilst if the right digits are removed, all that is lost is a level of precision - eg. from 1m square to a 10m square.
There are some documents on the Ordnance Survey that explain all this and more (eg. things like geoids).

My experience of MapPoint OS GRs is that it is consistent with the above.
I've had it working with 10 digit GRs - so pad each ordinate on the right hand side accordingly.
Try it, and check it is working as you expect.

For padding, padding SH75 out with zeros gives SH 7000050000 which is going to be the south west corner of the 10km square 'SH75'.

btw, MapPoint 2002 uses the wrong geoid for OS GR calculations - errors of 10-100m are common. The bug is fixed in MapPoint 2004.


Richard

__________________
Winwaed Software Technology LLC
http://www.winwaed.com
See http://www.mapping-tools.com for MapPoint Tools
Pre-Order MapPoint 2009 today: http://www.mapping-tools.com/mappoint2009

Richard,

Thanks for your comprehensive reply. I think I'm beginning to figure things out now!

MapPoint does still want leading zeros sometimes, but it's not padding, it's because I'm "in square zero". e.g. The Isles of Scilly are near 0,0 - and anything in a vertical line West of Scotland or horizontal in the Channel is similar for one coord. This explains the apparently inconsistent need for padding.

My source data has all leading zeros omitted - it may be Excel is to blame here - but I note also that streetmap.co.uk gives what it calls OSX & OSY similarly without the leading zero for anywhere in square zero etc. I think it assumes all OSGRs are 6 digit & adds leading zeroes where they're not??

Now I need to figure out how the North of Scotland is handled - i.e. beyond "9". It looks like MapPoint reads "10" as "10" if there's one more digit in the Northing than in the Easting (e.g. '0 10' or '00 100').

I've searched the OS web site thouroughly before and tried again today but not found anything useful like what you've told me. Everything assumes you are using the letter-based prefixes.

I hope I'm now making more sense?
Thanks again,

-Michael
(aka random)