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| Subject: | Re: [gislist] Advice on heads-up digitizing |
| Date: |
05/24/2007 10:23:45 AM |
| From: |
Glaser, Holly |
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Hi-
A couple of things to think about--
How big is the circle that is required to confidently contain a known
point?
This will give you an accuracy standard and USGS has scales that
correspond to each accuracy level
Check if there are any known monuments in or near your pictures.
The image can be warped to fit the monuments with georectification.
The RMS error is displayed when warping and should be less than your
accuracy standard.
Holly Glaser
www.wsdot.wa.gov/mapsdata/transframework/default.htm
-----Original Message-----
From: gislist-bounces@lists.geocomm.com
[mailto:gislist-bounces@lists.geocomm.com] On Behalf Of Gillian McGregor
Sent: Thursday, May 24, 2007 4:07 AM
To: gislist@lists.geocomm.com
Subject: [gislist] Advice on heads-up digitizing
Advice on heads-up digitizing in Arc9 - creating landuse data from black
and white aerial photos:
We are woking with time series photos, captured at a scale of 1:20 000
to about 1:50 000. The pixel size of the photos in their scanned form
is about 6mx6m. Pixelation is evident at a scale of about 1:12 000.
1. Can someone advise what would be a reasonable scale to digitize at,
and suggest how we would justify this choice?
2. Can anyone direct us to literature on the levels of error encountered
when using un-ortho-rectified images or advise based on experience?
Thanks
Gillian McGregor
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