[Gdal-dev] Warp / rotation

Ed McNierney ed at topozone.com
Tue Aug 19 16:47:30 EDT 2003

I think you missed the point - a rectangle rotated is no longer a rectangle.  It's a four-sided polygon, a quadrilateral, etc. - what's important is that you are requesting an area that, expressed in the source coordinate system, is not rectangular.  If the Y coordinates of the lower left and lower right corners are different, it's not a rectangle.
Can you provide a rigorous definition of your rotation?  "About 2 degrees CW" isn't precise enough.  If you can describe it mathematically, we can help you implement it!
    - Ed

-----Original Message-----
From: Geographic Wizard [mailto:geowiz at shaw.ca]
Sent: Tuesday, August 19, 2003 4:37 PM
To: gdal-dev at remotesensing.org
Subject: Re: [Gdal-dev] Warp / rotation

The coordinates in the sample are UTMs and the rectangle is a rectangle, just rotated. I guess what I am looking for is a quick and easy way to pull the subimage with a rotation applied, maybe.
These are UTM's, but they really could be any kind of coordinate.

----- Original Message ----- 
From: Ed McNierney <mailto:ed at topozone.com>  
To: gdal-dev at remotesensing.org 
Sent: Tuesday, August 19, 2003 11:10 AM
Subject: RE: [Gdal-dev] Warp / rotation

Dear Wizard -
The problem is that your "rectangle" isn't a rectangle!  You seem to be trying to reproject your image - can you describe the input and output projections you're using?  Those numbers make it look like your input data might be in UTM (but it could certainly be something else), but what is your desired output projection?
    - Ed
Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: Geographic Wizard [mailto:geowiz at shaw.ca]
Sent: Tuesday, August 19, 2003 12:58 PM
To: gdal-dev at remotesensing.org
Subject: [Gdal-dev] Warp / rotation

Hi, everybody
New to GDAL as well as using georeferenced raster images. I am trying to figure out how to do the following, and any help / insight would be greatly appreciated. I have put some numbers together as an example :
I have an image (tif/jpg/png) 5000 x 5000 that is georef with a world file
I would like to pull a sub image of this that is bound by a rectangle
 669273--------------------------- 670898
5862482--------------------------- 5862538
 669330--------------------------- 670956
I would like line # 1 of the sub-image to be along the top boundary of the rectangle, therefore it needs to be rotated by about 2 degrees cw.
Any help would be appreciated.

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