help needed on orthophoto

[Phisan Santitamnont]

Dear Jiao

jiao weili wrote:

>
> Thanks for your response.  If I have an image with large difference elevation,may I
> first do rectification with n-polynomial, and then use the DEM to correct the relief
> displace placement?  Could  the result be an orthoimage?
>

Of course, you can do rectification witn polynom degreen n but with
limit accuracy.

According to my experience with a -a e r i a l- photo
rectification with 3 degree polynom need about 20
ground control points to get as good as result
when compare with orthophoto using
'sparse DEM' with 5-6 control point.

In case of satellite image you have no choice.
You can only use polynom rectification.

If the terrain is moutaineous, you will
need more GCPs to get good result

Rgds,

--
Phisan Santitamnont, Dr.-Ing.
Survey Engineering Department
Chulalongkorn University
Pathumwan Rd, Bangkok 10330
Tel. +66 (2) 218 66 61
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