I know Google earth has a measuring tool, but I think it's just point and click. I've never found any way to manually enter in the way points for it.
Google Earth allows you to easily do many things you never thought possible. You can enter lat/long directly and it will immediately take you there, leaving a marker icon if you wish. You can use the line or path tool and it will plot points that you click in a continuous path, and give you the accumulated distance. I used it extensively when preparing for the Yukon 1000 mile canoe race. I easily plotted 678 waypoints and the path between them just by clicking my way down the river, then downloaded them all, complete with lat/long to a spreadsheet.
From some fairly complex spreadsheet calculations (with a variable fudge factor for turn radii among many other options), each waypoint was labeled with its distance from the race start in tenths of a mile, and whether a left turn or right turn was coming up (LT/RT). They and the route were then re-loaded with labels from excel spreadsheet back into Google Earth. I never had to manually type a single number.
During the non-paddling winter months I trained by watching GE "fly" the route down the river in GE 3-D mode on a wide screen TV while I worked out on a paddling machine. I wrote a set of instructions in the spreadsheet for analysis and location predictions based on real time SPOT inputs so my pit crew could accurately estimate location for any future time on the 6-day long race.
Next I loaded all 678 waypoints and route between them into a GPS. During the race it was easy to correlate GPS waypoints, named by their mile number, with a 95-page book of waterproofed printed maps showing the same labeled points, and to set us up to turn the canoe toward the next waypoint even before leaving the last point. In the end the final actual distance as measured by GPS and calculated GE distance were off by less than 2%. That can be corrected next time by adjusting the fudge factor.
Here is a section of the river with waypoints in the 700 mile range from Whitehorse. Satellite imagery and coordinate registration of the river is far more accurate than topographic maps because the topo maps date from the 1950's and GE images are less than five years old in most places. Note, the river itself is about 4 miles wide in this section. In some sections I plotted more than one possible side route through the ever changing islands and shallow shoals, choice to be determined by actual conditions when we got there.
(in case anyone wants to do this race, don't even think to ask me for my waypoint list or spreadsheet calculation - you will never pry them away from my cold paddle-curled fingers
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