MATLAB: How to generate a Hammer projection from the PNG image file using Mapping Toolbox 2.6 (R2007b)

displayfigurefileMapping Toolboxworld

I want to produce a map of a planet using the Hammer-Aitoff Projection. The example in the documentation for GEOSHOW produces a Hammer projection of the Earth using the shapes of the continents. However, there is nothing equivalent to oceans and continents for other planets so I cannot use contours of shapes.

Best Answer

If you have a PGW worldfile accompanying the PNG file, that will you to create a proper Hammer projection of the PNG image.
If you do not have a worldfile, then you can create a referencing matrix using the function MAKEREFMAT. Once you have a referencing matrix, you can read the data from the PNG file using IMREAD and use the image syntax for GEOSHOW.
For example, if the image covered the entire Earth and each pixel covered a one-degree-by-one-degree square, and the upper left corner of the image is at -180 degrees longitude and 90 degrees latitude, then:
lat11 =    89.5;  % Cell-center latitude  corresponding to image(1,1)
lon11 =  -179.5;  % Cell-center longitude corresponding to image(1,1)
dLat = -1;  % From row to row moving south by one degree
dLon = 1;  % From column to column moving east by one degree
R = makerefmat(lon11, lat11, dLon, dLat)
X = imread('myImage.png');
figure;
axesm ('hammer', 'Frame', 'on', 'Grid', 'on');
geoshow(X,R)
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