[Talk-GB] OS 7th series, accuracy update, request for calibration help
mapping at sheerman-chase.org.uk
Mon Oct 19 18:31:28 BST 2009
Thanks for the offers of help. The task is a very "on again, off again"
affair so expect quiet times and busy times! (Depending on availability
of new scans.) The steps are as follows:
1) Load map into gimp or similar. The images are 17000 by 21000 pixels
which can be a strain on computer memory.
2) Resize to 50% of orginal. This seems sufficient and makes later
stages faster to process.
3) Save as jpg
4) Note 9 calibration points that are appoximately evenly placed in a
3x3 grid. The map corners are used as calibration points. Each point has
a map reference and pixel position.
5) Save that information in a text file as specified here:
6) To check the calibration, the calibration file can be used with the
warp-gbos tool to create a KML file. The warp-gbos tool needs to be
compiled from source. Details at the above link.
7) This can be compared to google-earth as a sanity check.
8) Send me the calibration file :)
I will send people who have expressed an interest a link to download a
map sheet to play with.
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