The 3 you quote are the best free resources I know of.
There is another I know of from Cadimage - GDL Handbook.
I see it is now in it's 2nd release and now has a PDF version.
It is not free however and I think is more of an advanced GDL book.
http://www.cadimage.com/Products/Training/GDL-Handbook2
The GDL Cookbook I found to be the best.
A little outdated now but still relavent.
Follow the examples from the beginning and you will learn a lot.
Barry.
One of the forum moderators.
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