I am developing in the UK and I need a way of converting British Ordinance Survey Easting and Northing co-ordinates for placing pushpins in VB. Any ideas?

The European version of MapPoint supports OS Grid references. I think there are two or more slightly different OS Grid reference formats, and MapPoint only supports one (6-digit?) but I think there are conversion routines available for going from one format to the other.

The European Edition of MapPoint DOES NOT support OS Grid co-ordinates. :x

Or at least it should, but they are plotted incorrectly, with a 120-200metre error.

This is because the Eastings and Northings are converted to Latitude and Longditude WITHOUT any adjustment for the curvature of the earth. Plus MapPoint uses the American elipsoid model (GRS80/ETRS89/WGS84) and the OS Grid is based on the Airy 1830 Elipsoid model.

To convert Eastings and Northings for MapPoint you need to convert them to lat/long but using the (incorrect) WGS84 elipsoid model, apply the OSTN97 conversion to allow for the OS Grid being flat :roll: and then you'll have something that comes close.

My problem is that (a) MapPoint should damn well work and (b) my calcs have an error of up to 5 metres which makes the points plotted next to useless.

If you are picking up a disabled person, the vehicle needs to be on the right side of the road. Five metres would put you on the opposite pavement. Naff.

We are also having great difficulty plotting accurate pushpins into MapPoint.

At the moment we take in Northings and Eastings data, convert to long and lat and then plot a pushpin.

The pushpin seems to be around 100m away from where it should be. We have taken on board your comments of applying the OSTN97 conversion but are sturggling to find anywhere that will help us incorporate this into our c# code.

Any help would be more than appreciated.

The geoid error (the OSGR code used WGS84 instead of the correct Airy'36) is in MapPoint 2002, and was fixed in MapPoint 2004.

Also note that a six digit grid reference is only accurate to 100m - by definition. Eight digit will give you ten metres, and ten will give you 1 metre.
I think I tested MapPoint with 8 digit GRs from North Wales (because I have 1:10,000 OS maps of parts of Snowdonia), but it was a while ago.


Richard

it's a pain in the neck but do-able...
gat yourself a copy of the OS document on format conversion (cant remember the name, something like 'a guide to co-ordinate systems', downloadable from the os web site and start coding. I did it in vb5 so I don't suppose my code is a lot of use to you, but I created routines to convert WGS84 lat/lon (i.e. what you get from a GPS unit) into eastings/northings and vice-versa. The conversion process is not simple, allow a week of coding to get it right!
bear in mind the limited accuracy of GPS- 5 metres is asking a lot.
You might improve matters by using mappoint calls to determine the side of the road that the address is on?