Steve Hosgood writes: > > My only comment is just that 1937 maps will certainly be before the > National Grid was adopted, and will be based on the "old triangulation" > done between the late 1700's to mid 1800's. I don't know the details, > but it wasn't metric (possibly surveyed in "survey chains" or thousands > of yards or royal Babylonian cubits). > > The first OS maps based on the "new triangulation" (which was metric), > and with the now-familiar National Grid didn't appear to the public > until after WWII. > > Whether or not you can get an "old survey" map to line up with a "new > survey" map (or even with reality!) is not obvious. I'm not even sure if > the mapping projection of the pre WWII maps is the same as today's (i.e > Transverse Mercator based on the "Airy 1830" spheroid). It certainly > isn't WGS84 which IIRC is what FG's terrain is based on. >
Hmm, I've got a feeling that the 36 in OSGB36 might refer to 1936, in which case you are probably right - post-war maps should be OK - I've got no problem converting to and from WGS84 <==> OSGB36. It seems that 1" maps from the 7th series in the mid fifties to early sixties are fairly widely available - I guess that these are probably the best to go for at the moment. I will look out for one to a hilly area to try as a proof-of-concept. Regarding the rest of the thread - yes, the OS jealously guards copyright in the UK. Other agencies are just as bad - it was very difficult to find online tide tables for dates in the future last time I looked. I've heard the opinion given from a source that I respect that the OS regards vector data from non-OS aerial imagery that has been ortho-rectified using OS data to contain residual OS copyright. However, the 50 year expiry of Crown Copyright on published works (it's a lot longer on unpublished government material) is clearly stated on the OS website, so ultimately all their mapping is free to use - we just have to wait a while. Now that's the sort of development that I like the sound of ;-) I think that elevation and waterbody outlines from the 50s should be just fine though, and a major improvement on the current situation. Cheers - Dave ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
