... I loaded an old copy (circa 2005) of ACA Atlantic Coast route onto the Edge. The GPS calculated the route, navigated the road, and gave me turn-by-turn directions... That does not happen with the latest copy of that route. The Edge displays it in straight lines and gives cardinal directions. The distance to next turn and distance to destination are not accurate, because they are calculated over straight lines.
Why is that? Why did the old file work, but not the new? I found the new file has the <extensions> tag without the detailed route extensions. The Edge uses these extensions and was relying on them to provide the route details, but the details never came.
I edited the file to remove the empty extensions. I did that for just the first portion of the route A01010. Voilà. The Edge calculated the route, navigated the road, and gave me turn-by-turn directions.
Without spending a lot of time reloading the versions of MapSource that were current at these times and studying the files, I cannot answer why the old file worked, but not the new. I can say that MapSource had several GPX-related defects a couple of years ago, since fixed AFAIK. We did not notice the empty routepoint extensions, but this may well have been among them.
Now I am confused again. You wrote "The GPS calculated the route, navigated the road, and gave me turn-by-turn directions," but upthread you wrote "The Edge does not recalculate stored routes within the unit." I was under the impression that the Edge relies on the road navigation and turn-by-turn directions calculated by MapSource or BaseCamp. As I do not have an Edge, I rely on you to set me straight.
I can guess that whoever prepared one ACA route had MapSource set to follow roads and the other had MapSource set for straight line navigation. The Edge worked with what it was given.
No surprise that straight-line paths are shorter than road-following paths. As Using Adventure Cycling GPS Data > Considerations for Mapping Receivers
says at the top of the GPS Discussion group, "The straight-line distance to the next turn is a little less than the road distance, but close enough to see from the GPSR when the next turn should appear. Except for that, all the navigation functions are the same in straight-line and road-following navigation."
I noticed that for some reason route A01030 in AC01v007.gpx has the full extensions details. The Edge was very happy to find them and navigated properly on the road.
That is, to get the ACA routes to work better with the Edge, one needs to either remove the empty extensions or fill them up with the route details.
Again, it looks like the Edge works with what it is given. Given only the waypoints, it navigates straight lines. Given the breadcrumbs of the routepoint extensions, it uses them to navigate roads.
I wonder if this same behavior happens with other recent Garmin units in the Outdoors line of products. Any experience there, say with 2011 and 2012 models such as GPSMAP 62 and eTrex 30? Do the new units rely also on route-point extensions?
No. As I wrote upthread, "I looked for other receivers that are Garmin Mass Storage Mode devices with no luck. A Google search for Garmin Mass Storage Mode devices turns up a lot of confusion among developers..." Of course "rely on route-point extensions" and "use route-point extensions when they are available" are two different beasts. Garmin's product descriptions for most mapping handhelds include "Automatic routing (turn by turn routing on roads): yes (with optional mapping for detailed roads)." To me this means they do not rely on the PC to calculate paths, but who knows whether they use the extensions when available?