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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | Re: GISList: cell size for vector to grid conversion |
| Date: |
07/31/2001 11:34:27 PM |
| From: |
Peter Bayley |
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I'm only guessing here, but I would think the cell size ( in other words,
the sampling frequency) needs to be at least twice the minimum size of the
data iself (according to Nyquist). I would think the minimum data size is
best established by knowing the precision of the original vector data. If
the data was digitized at, say, 1:25,000 with an uncertainty of +/- 0.5mm
then the minimum data size would be 25000*(0.5/1000) or +/- 12.5 metres.
So I would choose a cell size of under half this - for example, 5m. The 1/4
area you mention probably comes from squaring the 1/2 cell side.
Might all be BS but it seems to make sense - at least for me
Have fun
Peter
----- Original Message -----
From: "Chris Garrard" <chrisg@biology.usu.edu>
To: "GISLIST (E-mail)" <gislist@geocomm.com>
Sent: Wednesday, 01 August, 2001 6:04 AM
Subject: GISList: cell size for vector to grid conversion
Hi all,
I'm looking for some references (peer-reviewed stuff, mostly) that
discuss vector to grid conversion. I'm especially interested in
choosing the appropriate cell size to minimize data loss, and choosing
the optimum cell size to balance data loss with storage space.
I've seen a reference to Piwowar (87) that states that the cell size
should be 1/4 the size of the minimum polygon, but I haven't yet been
able to get my hands on Piwowar's thesis. Does anyone know exactly what
this means? Do you use a cell size that is 1/4 the area of the smallest
polygon, or 1/4 the "diameter" of that polygon, or what?
I'd appreciate any comments or references.
Thanks,
Chris
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