[pct-l] PCT Atlas - Clarification Please

[Lon Cooper]

Brian,

I use a Garmin GPS, and Garmin software called Mapsource to view/edit
my GPS data. I then save the data as a .gpx file that is imported into
NG TOPO! to make the printable maps on pctmap.net.

When I say the log distance is 75.3 miles, that is the distance I see
in Garmin Mapsource when I open the track log. When the data is
converted to a NG TOPO! route it shows an even shorter distance...in
this case 73.8 miles. I have found NG TOPO! consistently reads shorter
than Garmin Mapsource with the same data. I always use the Garmin
software for distances because I think is more accurate. The only
thing I do in NG TOPO! is print and create labels on the maps.

If anyone is interested, you can download the gps log file and TOPO!
file (for the Border to Scissors) I have been discussing here:

http://www.pctmap.net/pctdownloads/scissors_test.zip

I am not sure it really matters if a 100 mile section of the PCT is
100 miles or 98 miles, except as AsABat suggest for clear
communication in things like the water report. It gives me confidence
in both my data and the Databook that they agree as closely as they
do.

-Lon
AKA Halfmile



On Feb 6, 2008 11:40 PM, Brian Lewis <brianle at nwlink.com> wrote:
> > My GPS log has the distance from the border to Scissors at 75.3 miles.
> >
> > My logs constantly show the trail distances 2 - 3% less than the
> > databook for the 1,000 miles of trial that I have logged so far.
>
> I find that using a GPS with NG Topo software pretty consistently gives
> distances about that amount less than what independent sources report it as.
> If I'm guessing correctly at your meaning here, Lon, I think that you're
> saying that you look at the GPS track built from waypoints and see what the
> Topo software says the distance is --- is that right?
>
> I suspect a couple of factors at work here (at least a couple).  One is
> whether the Topo software factors in uphill/downhill distance, or is looking
> at it "as a crow flies the plot".   Another is just that inevitably the
> track-built-from-waypoints is going to be a series of straightline segments,
> approximating but never fully conforming to all the twists and turns of the
> trail.
>
> Recalling calculus, I guess if the segments get short enough then your
> approximation gets better and better ... <g>
>
> Apologies in advance if you meant something different and I'm
> misinterpreting.
>
>
>
>         Brian Lewis
>
>
>
> _______________________________________________
> Pct-l mailing list
> Pct-l at backcountry.net
> To unsubscribe or change list options (digest, etc):
> http://mailman.backcountry.net/mailman/listinfo/pct-l
>