MATLAB: Does projfwd not work on some geotiff files

errorgeotiffMapping Toolboxprojfwd

I am working with a set of geoTIFF files. For some of them, I receive an error when I attempt to use the projfwd function (see below). I have little experience with the Mapping Toolbox and geoTIFF files and would appreciate any help better understanding this problem.

Error using proj2gtif (line 17) The GeoTIFF structure PROJ cannot be used with functions PROJFWD or PROJINV.

Error in projaccess (line 40) gtif = proj2gtif(proj);

Error in projfwd (line 60) [x,y] = projaccess('fwd', proj, lat, lon);

Best Answer

I believe I have discovered the problem. There are multiple types of geoTIFF files, each requiring different treatment. I've written how I handled the differences below. Note that my ultimate goal was to convert latitude and longitude data into pixel coordinates, which I call 'row' and 'col'.

%Get geoTIFF file information
info = geotiffinfo(geoTIFF_filename);
%Get geoTIFF image file data based on ColorType field of 'info'
switch lower(info.ColorType)
     case 'indexed'
          [~, ~, R] = geotiffread(geoTIFF_filename);
     otherwise
          [~, R] = geotiffread(geoTIFF_filename);
     end
   %Convert latitude and longitude to pixel coordinates based on class of R
   switch class(R)
        case 'map.rasterref.GeographicCellsReference'
             [row, col] = latlon2pix(R, lat, lon);
        case 'map.rasterref.MapCellsReference'
             [X, Y] = projfwd(info, lat, lon);
             [row, col] = map2pix(R, X, Y);
        otherwise
             error('Unrecognized format for R');
   end

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Hi Raghu,

As background information, the coordinates of your image are in a projected coordinate system rather than a geographic coordinate system. You can use the function GEOTIFFINFO to return the information structure.

You will see the 'ModelType' field set to 'ModelTypeProjected'; therefore, the RefMatrix is also referenced to map coordinates.

Beginning in R2011a, you will also see a new field, SpatialRef, which in this case will contain a spatialref.MapRasterReference object.

If you want to find the geographic coordinates from the map coordinates, then you need to use the function PROJINV to unproject the coordinates to latitude and longitude.

Here is how you would find the latitude and longitude values for the center of the first pixel in boston.tif:

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followed by:

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I hope this help you.

-Kelly

Best Answer

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