Georeferencing of maps

[Simon E]

I am currently working on the import of maps and courses for RG2. Wherever possible this will use georeferencing information from the map images and course files. This should make setting up an event and uploading GPS routes much easier.

It would be useful to know what co-ordinate system clubs are using for their maps (if any). I have gradually been migrating all HH maps to the British National Grid (OS), so this is the option currently supported. Some things it would be useful to know:

• Is anyone using anything other than the British National Grid?
• Are many clubs using georeferencing yet?

If you're not sure what this is about then there is a guide to georeferencing on the BOF website.

[Red Adder]

'fraid to say it seems a lot of work for the mapper for questionable benefit.

It also means that the OS have a definitive claim to be the map source. I don't use OS sources for my base maps - Prefer aerials that seem to have no OS input or even wheel / ranging rods and compass (on both school grounds and FC forests) to create the base. In Suffolk contours hardly apply so again the OS is not my source.

[Freefall]

Geo-referencing is essential if you want to use GPS to track athletes and display their location in real-time (as we did at Moray 2013). The OS has no copyright or IPR over the British National Grid so that is a non-issue. You can use a GPS and derive suitable coordinates and not go anywhere near an OS map source.

[dustytoo]

I georeference all new maps and older maps as and when I update them. This is using the National Grid as the coordinate system. This has two benefits. GPS recordings taken while surveying can be dropped straight onto the map, in more or less the right place, and after making due allowance for the error margin in GPS can be a very quick way of placing line and point features. Secondly, if you occasionally use data like LIDAR, this too can then be imported in exactly the right place. Locating a set of contours by hand, now that's a tough game!

[Angry Haggis]

OpenOrienteeringMap maps are in Spherical Mercator, aka EPSG900913 or the Google Maps projection. However they don't have any georeferencing information associated with them at the moment. I presume you would be looking for an associated TFW or PGW "world file" and a rasterised version of the map.

[Big Jon]

I georeference all new and revised maps on the British National Grid.

Main help in old maps is detecting distortions across the map and blocks where everything is twisted - surprising how many maps have major issues of this type!

[Simon E]

I presume you would be looking for an associated TFW or PGW "world file" and a rasterised version of the map.

Yes, that's what I have done so far. OCAD can export JPG, TIFF and GIF files with an associated world file, and from that I can derive the world file for WGS-84 to handle GPS files. The latest OCAD is meant to write proper geotiff files as well but I haven't got that to work yet.

In theory you could set up an RG2 event automatically at the same time that you create the OpenOrienteeringMap.That's certainly on the possible future developments list.