[Gdal-dev] Warp / rotation

[Geographic Wizard]

Ed,

I do mean grid convergence of the projection.

It sort of is lat / long except it isn't. Everything is projected to UTM, then localized to the center of the area and rotated by the grid convergence. Possibly all that I need to do is rotate the image, which again, I am not sure what would be the most efficient method.

Thanks for you patience.

Steve

  ----- Original Message ----- 
  From: Ed McNierney 
  To: gdal-dev at remotesensing.org 
  Sent: Tuesday, August 19, 2003 3:33 PM
  Subject: RE: [Gdal-dev] Warp / rotation


  Steve -

  Sorry, I don't mean to sound dense, but how do you define "convergence"?  Do you mean the grid convergence of the UTM projection (for example) at that point?

  It sounds like you might be trying to select an area that is a rectangle in latitude/longitude and then clipping that area out of the UTM source image and reprojecting the results to a "geographic" (lat/long) projection.  Is that correct?  If not, please set me straight - thanks!

      - Ed
    -----Original Message-----
    From: Geographic Wizard [mailto:geowiz at shaw.ca]
    Sent: Tuesday, August 19, 2003 5:00 PM
    To: gdal-dev at remotesensing.org
    Subject: Re: [Gdal-dev] Warp / rotation


    It'a a dynamic rotation, the convergence of whatever coordinate system you are woirking in, at the center of your area ot interest.

    Steve
      ----- Original Message ----- 
      From: Ed McNierney 
      To: gdal-dev at remotesensing.org 
      Sent: Tuesday, August 19, 2003 2:47 PM
      Subject: RE: [Gdal-dev] Warp / rotation


      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 
          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

            2
            0
            0
            -2
            667500
            5864000

            I would like to pull a sub image of this that is bound by a rectangle

             669273--------------------------- 670898
            5862482--------------------------- 5862538



             669330--------------------------- 670956
            5860859---------------------------5860910


            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.

            Thanks,
            Steve
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