I have data from 4 measurers so far, closely grouped. I found that practice makes perfect, and learned some tricks.
Here is how I think the best measurement evidence will be generated:
1. Using Google Earth, begin with a virgin map with nothing on it.
2. Using previous data, put a mark at the start and finish.
a. The Start is 616.42 feet north of the center of road T-549
b. The Finish is 128.9 feet north of the center of the driveway to the park. There is a very faint paintmark at the proper location, visible by squinting or using Street View.
3. With Start and Finish marked, measure the course in one go. When you are done, save the file as a GE .kmg file.
a. Click on the measure line and read the length in feet.
b. Use high magnification when needed at corners.
c. If path is obscured, go back in time, and get an unobscured view. This will not interrupt a measurement that you may have in progress.
d. If you make a "bad click" which is way off the line you want, just give it a right-click. Each right click will erase the last point entered. You don't have to start over!
The more times you do this the shorter will be the resultant measurement. Measure as tight as you can, but do not leave the road surface. Pretty soon you will see that you cannot improve significantly. You will have measured the SPR.
If you are satisfied that you have got it as good as you can, let me know and send me the kmg file. Remember - only one measure line in the file!
I have noticed that if I collect kmg’s in my GE program, clicking on one of them will sometimes give me the wrong kmg. So I store them in another folder, and save nothing in the GE program.