Originally Posted by
Looigi
FWIW: RWGPS, MMR, USGS, etc, have rather coarse granularity for elevation. You can go up and down a lot on a ride without crossing a contour line every time. A Garmin with a barometric sensor will add this in, mapping websites may not. As a result the Garmin will always show more elevation gain than the websites.
Thats the thing though...the garmin is showing about the same compared to the sites data, but with the correction from RWGPS shows at the 3 points i compared to the USGS tool within 3-5'. I can use the usgs tool going up a hill i ride and it might show 969' and go up the.hill 30' and it show 971. I dont think the USGS site is going off a contour line, or at the least, has an accurate way to measure elevation exactly at the marker
Ill pull up the tool i used once i get home, see if i can look up elevation benchmarks and then see what the website marks them at.
And FWIW, heres some info on the dam we ride from...the parking lot on the west side of the dam, we ride from there, across the dam. The lot is pretty close to the same level (maybe a few feet if that) as the bridge over the dam. This article says top of the dam is 911' in elevation, so i can definitely see 25-30' drop from the bridge/path down to the water level/top of the dam
http://en.wikipedia.org/wiki/Hoover_Dam_(Ohio)