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General Category => Using The Maps/Garmin Software => Topic started by: hwstock on September 18, 2014, 07:34:22 AM

Title: error in caltopo 2011 near Humphreys Peak in Sierra (west of Bishop)
Post by: hwstock on September 18, 2014, 07:34:22 AM
This look like the same sort of error I found 2 years back for the NV maps near Desatoya Twins

Below is a screenshot for ExpertGPS of tracks that I know go to the summit of Humphreys Peak; check the dark blue track:
http://hwstock.org/err/realhump.jpg

Now here is the screen shot for the same track on the Garmin 62sc:
http://hwstock.org/err/62stc.jpg

The caltopo map contours are displaced by about 300' in x-y



I haven't figured out what caused the error.  The contours for nearby Mt Emerson are right on the spot; that's on the next topo sheet (24k) south.
Title: Re: error in caltopo 2011 near Humphreys Peak in Sierra (west of Bishop)
Post by: maps4gps on September 19, 2014, 12:40:08 PM
Likely the USGS digital elevation file used to create the contours was in error.  USGS has used 9 or more methods to create these files; the older ones not being so good/accurate.

Occasionally even files created by the best methods with have a glitch.
Title: Re: error in caltopo 2011 near Humphreys Peak in Sierra (west of Bishop)
Post by: hwstock on September 19, 2014, 01:43:00 PM
Thanks for trying so hard.  I find errors all the time in usgs data.