I have been trying to write a program to perform the named projection but am having some problems where the texture is joined. I posted a thread on this cartography site http://www.cartotalk.com/index.php?showtopic=8330 as I was having problems with mapping initially but I think my mapping is now working I just have a problem with repeating texture coordinates.
Here are some screenshots. There is just some detracting distortion where the image is joined along the date line (the edge of the image):
I think the problem problem is due to the wrapping of texture coordinates. I have tried to illustrate the problem in the figure below. The program is currently mapping from A–>B so the distorted sectors are displaying a compressed version of nearly the entire map. What should happen instead is to map from A wrapping to B (to the right). In OpenGL I think this can be achieved by enabling GL_REPEAT and simple using that B’=B+1 to get the correct texture response.
But when I added this check:
if (p_d[n].u < p_d[n-1].u) p_d[n].u += 1;
only the problem from one of the polar aspects was fixed (and not at all from oblique aspects).
Any ideas? Here is a link to the program I have so far if it will help with diagnoses: http://dl.dropbox.com/u/49415695/Desktop5%…ery.close%5D.7z
You will need the data folder with the image (and maybe some dll files I haven’t included). The arrow keys control the centre of the projection, ‘t’ toggles the texture, ‘up-pg’ ‘dn-pg’ zoom in and out.