Thread #20985 / / Total number of messages: 3 / Thread View Count: 664 / Add thread to favorites:
AnonymousUser 20985 9 Hell Neck either
This photo appears to be from directly overhead. It was
given me by a friend, but for
which I have no data such as height above ground or type and
characteristics of the camera
and lense. It may have been taken in connection with County
aerial photo mapping work.
Would now like to use it, if possible, to layout a plot of a
vacant lot between myself
and a neighbor, to see if it could accomodate a dwelling, a
well and a septic system and
100ft setback from our river front in a manner meeting
county requirements for separation
between these items. The lot is waterfront and rather narrow
with limited room to
maneuver, but could perhaps be designed to keep within the
requirements in a close fitting
Have tried to generate a scaling factor from a few measured
features, such as our
existing buildings, docks and boundry markers, in the photo,
but find it varies quite
widely over the area, enough to prevent conclusive
determination of critical distances for
fitting the "pieces " together. Have tried averaging from
different points in the photo,
and, in Corel XARA, tried abit of distortion such as
applying a trapazoidal "mold" to squeeze some area's in
trapazoidal fashion, to find a scaling factor that would
hold with confidence over thewhole area, but was not
successful. Lot is only 105 ft wide and some separations are
on a100 ft radius from items both from within the lot and
from existing items on our two
adjoining lots. Fairly good accuracy is therefore required.
Can anybody suggest a way to "rectify" this image to
obtain a scaling factor food for the whole area, without
getting too technical in Aerial Photo map making?
Re: Hell Neck
my research group does a lot of aerial imaging and mapping.
There are a variety of ways that geometric distortions can
be introduced into aerial photos. One is lens distortion.
Another is through distortion in the scanning process. It
seems, however, that your biggest problem is that the photo
is oblique (ie., not taken straight down from above). This
type of distortion can be "backed out" with variable
results. You have already tried the simplest and most
obvious methods. To do more than this requires fairly
specialized software packages and accurate measurements of
topography and features within the picture. For a one off
case like this it would be easier and far less expensive to
go out and make your measurements by hand...
I'm afraid you're trying to turn a pigs ear into a silk purse.
My advice (if you want to pursue the aerial photo mapping)
would be to find a source for straight down photographs. If
www.terraserver.com doesn't have the required resolution you
might want to try contacting the USGS, FSA, or some local
Wish I could be of more help.
Re: Hell Neck
Thanks very much Stu. Now I can fahgettaboutit and try some
Bob Decker ;-)
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