[Talk-GB] NPE Tracing Update
Nick Burch
openstreetmap at gagravarr.org
Wed Mar 14 22:52:47 GMT 2007
On Wed, 14 Mar 2007, Bruce Cowan wrote:
> Thanks for this effort, but there seems to be something wrong with the
> Glasgow map [1] on the GPX tracer. If you try to trace a bit of this
> map, there is only one 4-way grid join on a given section as opposed to
> the usual 4.
Yup, that's the case for Glasgow, and IIRC somewhere in the Shetlands.
Those two are actually maps in the old Cassini system, re-projected by
Andy onto the National grid. For now, just hope they're well calibrated
(they seem to be). Longer term, we'll be replacing them with newer maps
(the Glasgow one is 1925, compared to late 1940s / early 1950s for the
others)
> This is good news, but I am not quite sure how this works. If I
> download a map (near Glasgow at least), I can never align it properly to
> known features.
I'm starting to think that the josm plugin has a bug. I hadn't really used
it until recently, and it does seem to be having bad calibration problems
for cases where the actual maps are well aligned. Perhaps the person who
wrote it can comment, whoever they are!
> Also, what do the blue crosses and white grid squares mean? I assume
> you need to line them up.
The blue crosses are where it thinks the tiles should meet. If it's
projecting properly, they should almost meet, and need a tiny tweak in a
few cases. If it's projecting the tiles wrong, very few of them will
meet...
Nick
More information about the Talk-GB
mailing list