I ran across a couple of pieces of info I’d thought I’d pass on. At one point I think it was mentioned about splitting the data transfer task in more parallel pipes. Specifically I wondered if you could move 8 bits of data to 8 strips by moving memory to a whole port at a time. Well it’s been done for the WS2811 and using a Teensy.
http://www.pjrc.com/teensy/td_libs_OctoWS2811.html
Of course even if you can update all the LEDs desired quickly enough to get a “good” H resolution, that’s not the whole story. The strips use PWM to get their myriad of colors and if the PWM is done too slowly, the PWM on/off timing will be visible as “sub-pixels”. Heck even that assumes you can run an entire PWM cycle, all 255 intervals for 8 bit, before the next update cycle. I found this table of controllers and their various specs.
http://code.google.com/p/fastspi/wiki/ChipsetOverview
Seems the WS2811 is only 400 Hz. Gack !! I’m not sure whether that chart means the PWM clock or the rate at which a whole PWM period is completed. The latter is the best case and so let’s assume for the moment that all 255 intervals are done in the 1/400 = 2.5 msec. That means updating the display sooner than every 2.5 msec won’t allow the PWM to complete. In a static display this would result in the wrong color/brightness. How far would your globe rotate in 2.5 msec ? At 30 revs/sec, it’s 2.5/33.33 360 deg = 27 deg. That seems a tad large for a good H resolution (aka H pixel size). And that’s the best case. What if the table means the PWM clock runs at 400 Hz and it really takes 1/400255 = 637.5 msec.
It would seem the fastest controller in the chart runs a PWM at 7kHz, 17.5x faster. In the best case that would yeild a H pixel size of about 1.5 deg … pretty close to what you had wanted. The TM1829 even updates 2x faster than the WS2811 and also does 8 bit/channel color. 1.5 deg equates to about 0.17" of arc length at the equator for your 1m in circumference globe. Visible at close viewing distances, not so much at 10’. Would the “subpixel” problem be visible ? Depends on the viewing distance. But this is the best case … what if the PWM clock is 7kHz and it really takes 255x longer to work through a whole PWM cycle ? Then everything is 255x longer and I think you’re screwed again, at least as far as getting it done “easily”.