Scanning resolution

Lester Caine lester at LSCES.CO.UK
Wed Dec 7 04:06:22 EST 2005


OK - I have probably gone OTT on this, but I've got the first map for my 
archive scanned and the raw tiff's are looking good. It's the Contour 
Motoring Map of BRITISH ISLES published by the AA in 1920. (16miles to 
Inch) A single page covering the whole country, 101mm by 90mm and I have 
a scan of it in 40 tiles approximately 5200 by 9600 pixels - 1200 dpi. 
The resulting data set is 4.3Gb ;) So I think we are talking a DVD 
rather than a CD :)

Question 1
I will maintain the raw scans at that resolution, as it is easy to 
achieve, and allows me to adjust alignment so that all the tiles are 
'vertical', but should I be looking to scale the raw images to a lower 
resolution for general use (CD size rather than DVD)

Question 2
The next step is to produce the geotiff data so that the map will appear 
as a single layer in MapServer. With reference to the resolution, will I 
be better off splitting the 40 tiles (currently around 100Mb each) into 
small chunks of say 20Mb each (2600x3200 approx)

Question3
I currently have an overview of the whole map which is 800x900 pixels 
(40 108x183 tiles) what would be the best method of scaling to cover 
intermediate scales, produce just one more 'scale', or a couple?

What ever I do now will determine how I handle a stack of some 300 other 
OS and Bartholomew maps I have that are already out of copyright, and 
about the same again that will 'become available' over the next 10 
years. Given that the data sets are going to be large, I will have to 
charge for CD/DVD copies, but the plan is to have a low resolution copy 
of each map available for free download.
http://home.lsces.co.uk/Maps/AASeries/BritishIsles1920/AABritishIsles1920Index.html
Be warned I've only got a 256k uplink so the high res sample of the Isle 
of Map will take a time to download :(

As a slight aside to the main questions - can someone point me to a good 
'beginners guide' to building the geotiff data - flat tiles first, I'll 
worry about projection later ;)

-- 
Lester Caine
-----------------------------
L.S.Caine Electronic Services
Treasurer - Firebird Foundation Inc.



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