GDAL GetGeoTransform Documentation — Is there an oversight, or what am I misunderstanding?












1















The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.




Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.



Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];


In a north up image, padfTransform[1] is the pixel width, and padfTransform[5] is the pixel height.



The upper left corner of the upper left pixel is at position (padfTransform[0],padfTransform[3]).



The default transform is (0,1,0,0,0,1) and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.




If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.



Here is my question:



So should the equation for Yp be:



Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];


in which the positions of L and P are swapped?



Or if I am confused about something, can someone help me get unconfused?










share|improve this question





























    1















    The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.




    Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.



    Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
    Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];


    In a north up image, padfTransform[1] is the pixel width, and padfTransform[5] is the pixel height.



    The upper left corner of the upper left pixel is at position (padfTransform[0],padfTransform[3]).



    The default transform is (0,1,0,0,0,1) and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.




    If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.



    Here is my question:



    So should the equation for Yp be:



    Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];


    in which the positions of L and P are swapped?



    Or if I am confused about something, can someone help me get unconfused?










    share|improve this question



























      1












      1








      1








      The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.




      Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.



      Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
      Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];


      In a north up image, padfTransform[1] is the pixel width, and padfTransform[5] is the pixel height.



      The upper left corner of the upper left pixel is at position (padfTransform[0],padfTransform[3]).



      The default transform is (0,1,0,0,0,1) and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.




      If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.



      Here is my question:



      So should the equation for Yp be:



      Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];


      in which the positions of L and P are swapped?



      Or if I am confused about something, can someone help me get unconfused?










      share|improve this question
















      The documentation for GDALDataset::GetGeoTransform says some things that are rather confusing.




      Fetches the coefficients for transforming between pixel/line (P,L) raster space, and projection coordinates (Xp,Yp) space.



      Xp = padfTransform[0] + P*padfTransform[1] + L*padfTransform[2];
      Yp = padfTransform[3] + P*padfTransform[4] + L*padfTransform[5];


      In a north up image, padfTransform[1] is the pixel width, and padfTransform[5] is the pixel height.



      The upper left corner of the upper left pixel is at position (padfTransform[0],padfTransform[3]).



      The default transform is (0,1,0,0,0,1) and should be returned even when a CE_Failure error is returned, such as for formats that don't support transformation to projection coordinates.




      If this is a matrix, it makes sense that Pixel_X is at 1,1 and Pixel_Y is at 2,2.



      Here is my question:



      So should the equation for Yp be:



      Yp = padfTransform[3] + L*padfTransform[4] + P*padfTransform[5];


      in which the positions of L and P are swapped?



      Or if I am confused about something, can someone help me get unconfused?







      gdal documentation






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 2 hours ago









      user2856

      30.1k258105




      30.1k258105










      asked 3 hours ago









      philologonphilologon

      1205




      1205






















          1 Answer
          1






          active

          oldest

          votes


















          3














          No.



          For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:



          Xp = padfTransform[0] + P*padfTransform[1];
          Yp = padfTransform[3] + L*padfTransform[5];

          # Where P = column number and L = row number


          i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).



          The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.






          share|improve this answer


























          • That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

            – philologon
            2 hours ago






          • 1





            @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

            – Mike T
            2 hours ago











          • Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

            – philologon
            2 hours ago











          Your Answer








          StackExchange.ready(function() {
          var channelOptions = {
          tags: "".split(" "),
          id: "79"
          };
          initTagRenderer("".split(" "), "".split(" "), channelOptions);

          StackExchange.using("externalEditor", function() {
          // Have to fire editor after snippets, if snippets enabled
          if (StackExchange.settings.snippets.snippetsEnabled) {
          StackExchange.using("snippets", function() {
          createEditor();
          });
          }
          else {
          createEditor();
          }
          });

          function createEditor() {
          StackExchange.prepareEditor({
          heartbeatType: 'answer',
          autoActivateHeartbeat: false,
          convertImagesToLinks: false,
          noModals: true,
          showLowRepImageUploadWarning: true,
          reputationToPostImages: null,
          bindNavPrevention: true,
          postfix: "",
          imageUploader: {
          brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
          contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
          allowUrls: true
          },
          onDemand: true,
          discardSelector: ".discard-answer"
          ,immediatelyShowMarkdownHelp:true
          });


          }
          });














          draft saved

          draft discarded


















          StackExchange.ready(
          function () {
          StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fgis.stackexchange.com%2fquestions%2f314654%2fgdal-getgeotransform-documentation-is-there-an-oversight-or-what-am-i-misund%23new-answer', 'question_page');
          }
          );

          Post as a guest















          Required, but never shown

























          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          3














          No.



          For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:



          Xp = padfTransform[0] + P*padfTransform[1];
          Yp = padfTransform[3] + L*padfTransform[5];

          # Where P = column number and L = row number


          i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).



          The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.






          share|improve this answer


























          • That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

            – philologon
            2 hours ago






          • 1





            @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

            – Mike T
            2 hours ago











          • Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

            – philologon
            2 hours ago
















          3














          No.



          For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:



          Xp = padfTransform[0] + P*padfTransform[1];
          Yp = padfTransform[3] + L*padfTransform[5];

          # Where P = column number and L = row number


          i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).



          The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.






          share|improve this answer


























          • That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

            – philologon
            2 hours ago






          • 1





            @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

            – Mike T
            2 hours ago











          • Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

            – philologon
            2 hours ago














          3












          3








          3







          No.



          For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:



          Xp = padfTransform[0] + P*padfTransform[1];
          Yp = padfTransform[3] + L*padfTransform[5];

          # Where P = column number and L = row number


          i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).



          The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.






          share|improve this answer















          No.



          For a north up image with no rotation (i.e. padfTransform[4] == padfTransform[2] == 0), the formula simply becomes:



          Xp = padfTransform[0] + P*padfTransform[1];
          Yp = padfTransform[3] + L*padfTransform[5];

          # Where P = column number and L = row number


          i.e add the starting X (or Y) to the column (or row) number multiplied by the pixel width (or height).



          The rotation terms may be what's tripping you up...? When a pixel is rotated, the Y skew needs to be considered when calculating the X map coordinate and the X skew needs to be considered when calculating the Y map coordinate. There's a quite detailed explanation in the wikipedia article on world files.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 1 hour ago

























          answered 2 hours ago









          user2856user2856

          30.1k258105




          30.1k258105













          • That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

            – philologon
            2 hours ago






          • 1





            @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

            – Mike T
            2 hours ago











          • Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

            – philologon
            2 hours ago



















          • That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

            – philologon
            2 hours ago






          • 1





            @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

            – Mike T
            2 hours ago











          • Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

            – philologon
            2 hours ago

















          That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

          – philologon
          2 hours ago





          That there is rotation is what was tripping me up. So can you tell me what P and L stand for? I naively supposed that P was Pixel dimension and L was Line dimension (the lines between pixels). Yes, that is as foolish as a sophomore reasoning with senior. In that vein, what do those letters stand for?

          – philologon
          2 hours ago




          1




          1





          @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

          – Mike T
          2 hours ago





          @philologon P is column number, and L is row number. These are "coordinates" on the raster image.

          – Mike T
          2 hours ago













          Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

          – philologon
          2 hours ago





          Thanks. I now see it is right there in the documentation. I always find a way to embarrass myself in these kinds of things, usually by skimming too fast.

          – philologon
          2 hours ago


















          draft saved

          draft discarded




















































          Thanks for contributing an answer to Geographic Information Systems Stack Exchange!


          • Please be sure to answer the question. Provide details and share your research!

          But avoid



          • Asking for help, clarification, or responding to other answers.

          • Making statements based on opinion; back them up with references or personal experience.


          To learn more, see our tips on writing great answers.




          draft saved


          draft discarded














          StackExchange.ready(
          function () {
          StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fgis.stackexchange.com%2fquestions%2f314654%2fgdal-getgeotransform-documentation-is-there-an-oversight-or-what-am-i-misund%23new-answer', 'question_page');
          }
          );

          Post as a guest















          Required, but never shown





















































          Required, but never shown














          Required, but never shown












          Required, but never shown







          Required, but never shown

































          Required, but never shown














          Required, but never shown












          Required, but never shown







          Required, but never shown







          Popular posts from this blog

          404 Error Contact Form 7 ajax form submitting

          How to know if a Active Directory user can login interactively

          TypeError: fit_transform() missing 1 required positional argument: 'X'