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| GeoCommunity Mailing List |
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| Subject: | Re: GISList: Remote Sensing |
| Date: |
02/13/2002 07:37:17 AM |
| From: |
David.Irving .. santos.com |
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I would regard what is suggested here as _highly_ dubious. Having worked as
a photogrammetrist and cartographic draughtsman, I know how reliable
contours and watercourses are likely to be, especially by the time they're
printed. The contours are accurate to within half a contour interval
(generally), so you can't reliably interpolate the intermediate contours
(they'll have a potential error of a whole contour interval). The
watercouses also will have been generalised, by both the photogrammetrist
and the draughtsman, so their positional accuracy is limited. For example,
they should be within 25m of their planimetric position on a 1:50,000 map
made to whatever the military standard is (it's been a while).
The short answer is, don't do it. There are excellent technical reasons for
this, which I have alluded to, and which should be explained in tiresome
detail in any decent cartography text book.
Regards,
David
David Irving
Systems Analyst
Shared Services
Santos Ltd
91 King William St
Adelaide SA 5000
Ph : 61 8 8224 7810
Fax: 61 8 8218 5960
BBitters1@aol
.com To: prabhakar@pun.cmc.net.in
cc: gislist@geocomm.com
24/01/2002 bcc:
22:20 Subject: Re: GISList: Remote Sensing
Prabhakar Rao,
It is acceptable to interpolate elevation values
at half the published contour interval. Remember
this is interpolation. Interpolation is a form
of estimation and there are automatic built-in
inaccuracies.
Using other map detail, for instance linear
hydrography, one can safely interpolate down
to one-tenth of a contour interval. This process
can only be performed within close proximity
of linear hydro features. It can not be applied
over the entire area of the map. This is also
an imprecise procedure but provides reasonable
results.
Best regards,
Barry
----------------------------------------------------------
Barry Bitters
Dept. Environ. Studies phone: (850) 936-1060
University of West Florida fax: (850) 936-1060
11000 University Parkway
Pensacola, Florida 32514 bbitters@uwf.edu
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