1. Ted Blank IOTA Conference Carson City, NV September, 2017
Using a Portable GPS To Determine Distance to the Centerline in the Field
Ted Blank
IOTA Conference
Carson City, NV
September, 2017

2. 80 km You have chosen a chord, Center Line calculated the distance,
perhaps even visited the site
or checked it out on Google
Street View.
Center Line

3. X X 80 km However, upon getting close to your site, you find out
that the road you chose is
closed due to flood damage! X X
80 km

4. ? X X There’s another road that crosses your chord, but
how will you know when
you are the proper distance
from the center line? ? X X

5. You will need a portable GPS unit which can display “Off-Course Distance”
Garmin GPSMap 64
Garmin eTrex 10, 20, 30
Garmin “Montana”
Garmin “Oregon”

6. Use Occult 4’s option to export the path of the centerline in “GPX” format.

9. Track File

10. Edit the “Track File” Open .TRX file in Wordpad Five “track segments”
First segment is center line
Keep this segment.
(Trim to <250 points)
Delete the other four
segments, which represent
the 1-sigma and 2-sigma
lines

11. Be careful not to delete these last two lines
Save file

12. Convert the Track File to a “Route File” using website:
- Register (free)
- Select “Convert” from GPS Track to GPS Route

14. Download and install free Garmin “Basecamp” software

15. Import your “route” file into Basecamp, and plug in your portable device

16. Device
Route File

17. Select and use the “Route”
you have just downloaded to
the handheld device.
Set up the device to display the
“Off Course” distance on the map.
You will now know your
perpendicular distance to the
center line at all times.