|
|
| GeoCommunity Mailing List |
| |
| Mailing List Archives |
| Subject: | RE: GISList: orthorectifying vs. triangulated warping |
| Date: |
08/30/2002 05:28:41 AM |
| From: |
Tomaz Skrbinsek |
|
|
It all depends on your terrain and your image. The problem is radial
deformation: When you make an aerial photo, your 3D terrain gets
projected on a 2D surface. This is ok in the center of your photograph,
as the light reflected from the terrain is perpendicular to both the
photograph and the terrain. The problem occurs toward the edges, since
the points that have higher elevation get projected outward relative to
the points with lower elevation, which get projected inward. For
example, imagine looking at a tall industrial chimney from a hill. The
base of the chimney seems where it should be, on the ground. The top of
the chimney, if you imagine this as a 2D photo, lies on the fields far
beyond the base. The same thing happens to the terrain.
So, the radial deformation depends on the altitude of the camera (lower
the altitude, higher the deformation), differences in terrain elevations
(higher the differences, higher the deformation) and view angle of the
camera (wider the angle, higher the deformation toward the edges).
So, ideally, if your terrain was flat as a pancake, or if the photograph
was taken from infinite distance, ortorectifying would do exactly the
same as warping. The difference between the both procedures is that
ortorectification takes into account the radial deformation and corrects
it (so, you will need a DEM of the area you want to ortorectify, camera
flight altitude and camera lens parameters), while warping just does a
rubber sheet warp based on a limited amount of reference points.
It all depends on your image and your application: if you have a
satellite photo, than you get quite close to having your camera at an
infinite altitude above the terrain, so the warping routine actually
does a pretty good job. However, if you have an aerial photograph taken
from an airplane, the radial deformation really kicks in and you can
pretty much forget warping if you want to have any precision in your
final image. Still, if your terrain is really flat, you might get a
fairly decent result. It may also work if you need your image only for
presentation purposes and you're not really concerned about precision.
You can read more about the topic in practically any book on basic
remote sensing. I apologize if the terminology I used in this
explanation is incorrect, since I've studied the subject in another
language.
Regards,
Tomaz.
-----------------------------------------------------------------------
bine@kibla.org Sometimes I think the surest sign
that intelligent life exists elsewhere
Tomaz Skrbinsek is the fact that none of it has tried to contact us
-----------------------------------------------------------------------
> -----Original Message-----
> From: Viktoras Didziulis [mailto:firekv@hotmail.com]
> Sent: Friday, August 30, 2002 7:51 AM
> To: gislist@geocomm.com
> Subject: GISList: orthorectifying vs. triangulated warping
>
> Actualy is there really a big difference in an outcomming result using
a
> "real" orthorectifying routine and image warping with triangulation
> algorithm having dense grid of refference points ?
>
> Viktoras
>
>
> _________________________________________________________________
> MSN Photos is the easiest way to share and print your photos:
> http://photos.msn.com/support/worldwide.aspx
>
>
>
> To unsubscribe, write to gislist-unsubscribe@geocomm.com
>
________________________________________________________________________
> GeoCommunity GeoBids - less than $1 per day!
> Get Access to the latest GIS & Geospatial Industry RFPs and bids
> http://www.geobids.com
>
> Setup a GeoCommunity Account and have access to
> the GISDataDepot DRG & DOQQ Catalog
> http://www.geocomm.com/login.php
To unsubscribe, write to gislist-unsubscribe@geocomm.com
________________________________________________________________________
GeoCommunity GeoBids - less than $1 per day!
Get Access to the latest GIS & Geospatial Industry RFPs and bids
http://www.geobids.com
Setup a GeoCommunity Account and have access to
the GISDataDepot DRG & DOQQ Catalog
http://www.geocomm.com/login.php
|
|
Sponsored by:
For information
regarding
advertising rates
Click Here!
|
