Experimental Glass and Approaches

As a budding IFR pilot, I am wondering where the information for the "highway in the sky" boxes comes from. Are they derived from the GPS approach plate information or are they just a nice path from your present position to the runway (or the missed approach point)? That obviously makes a difference if you are looking at an approach over something other than flat, towerless terrain.

What about an airport that does not have a GPS approach? Do the boxes take into account the descents between fixes - sort of dive down to the next box? Or do they synthesize a constant angle descent?

That specific information from the manufacturers seems to be lost in the glare of the "for situational awareness only" messages (driven no doubt by the liability concerns).

Any information would be much appreciated.

Stan

N67SL (reserved)
RV-7A (wings, QB fuse in a big box)
KCCB

On the GRT system, it's calculated based on 3 degree slope... and it doesnt' guarantee terrain clearance, so you would wanna be very careful following it in other-than-flat areas..

it uses GPS for some of these calculations..but again.. no terrain clearance guaranteed.