@TerryRitchie
First I want to emphasize my update to my reply to you yesterday that I think we are taking points on the circle (fill) and seeking the equivalent point for color on the rectangular image and the tu and tv are helpers to that translation/conversion. We are not likely taking all the points from a section of the image and plotting them by color into the circle fill, they wouldn't all fit!
2nd about the 3 and the 6. The circumference of a circle is 2*Pi*R = 6.28.... * R almost 6.
You need Pi*R displayed for the front of the globe = 3.14 *R
So the 3 and 6 are simplifications of Pi and 2*Pi is my guess.
As far as attributions go, I wonder if Paul Dunn stole/studied/and applied the above You Tube code from some other source say Richard Russel who has been doing spinning globes forever with BBC Basic. I say this because I see a couple of my works included in his You Tube collection
Like I said, "We stand on the shoulders of Copiers, not so much giants as knowers of good code when they see it and can figure out how to make it work for themselves carrying it forward with tiny improvements." This is why beginning artists are trained to copy the Masters, not to do that for their entire career but to carry great ideas forward to higher realms.
First I want to emphasize my update to my reply to you yesterday that I think we are taking points on the circle (fill) and seeking the equivalent point for color on the rectangular image and the tu and tv are helpers to that translation/conversion. We are not likely taking all the points from a section of the image and plotting them by color into the circle fill, they wouldn't all fit!
2nd about the 3 and the 6. The circumference of a circle is 2*Pi*R = 6.28.... * R almost 6.
You need Pi*R displayed for the front of the globe = 3.14 *R
So the 3 and 6 are simplifications of Pi and 2*Pi is my guess.
As far as attributions go, I wonder if Paul Dunn stole/studied/and applied the above You Tube code from some other source say Richard Russel who has been doing spinning globes forever with BBC Basic. I say this because I see a couple of my works included in his You Tube collection
Like I said, "We stand on the shoulders of Copiers, not so much giants as knowers of good code when they see it and can figure out how to make it work for themselves carrying it forward with tiny improvements." This is why beginning artists are trained to copy the Masters, not to do that for their entire career but to carry great ideas forward to higher realms.
b = b + ...