[GeoStL] ExpertGPS and Scanned Maps
- From: BruceS <bruces3418@xxxxxxxxx>
- To: geocaching@xxxxxxxxxxxxx
- Date: Sun, 5 Jun 2005 12:53:44 -0500
-
For those of you that have ExpertGPS and have wondered how/when to use
scanned map functionality, I have finally figured it out.
I have been planning some backpacking trips on the Ozark trail and
they have a very nice collection of maps for the the trail (
http://www.ozarktrail.com ), these maps are actually jpeg files from
the National Geographic Topo program. The difficulty was to able to
figure out waypoint along the trail to help with navigation. I could
have printed the utm maps and used a map protractor and done it with
some time. I could have also tried to trace the trail over to the
maps in ExpertGPS but his would have been very time consuming.
Instead I tried the scanned map function in ExpertGPS. This allows
you to calibrate the jpeg file to real lats and longs. All that you
need is to have 3 known points on the image. This was easy with these
maps as I could look at the topo maps downloaded by ExpertGPS and
finding the corresponding points on the scanned Topo image. I used
the dd mm ss version of the downloads from ozarktrail.com and after
calibration the minute gridlines in ExpertGPS lined up almost exactly
with the minute ticks on the downloaded image. So now I have a fully
calibrated image that shows where the trail is and can add waypoints
that I can then upload to my gps with some confidence.
The scanned map function will work with any jpg picture including
maps or aerial photos as long as you can identify 3 known points (2
will work fairly well but 3 is better) and they are drawn to scale.
I figured I would share this just in case someone else had seen this
listed ExpertGPS but didn't know how or why to use it.
Bruce
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