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Calibrating a map that is not 'True North' (PathAway 4.x)

Posted: Wed Mar 21, 2007 6:30 am
by msjfb
I have scanned maps I have for an upcoming boating trip. North is not 'up' on the maps.
Am I correct in understanding that I can use the scans 'as is' if I calibrate them in Map Manager using the 'known points' method and a minimum of 3 points ?

If not and I have to rotate the maps before calibrating, anyone have any suggestions as to how to do this ?

EDIT: When I say true north, I mean North is not straight up on the map.. Not a question about Magnetic North vs True North.

Thanks,

Frank

Posted: Wed Mar 21, 2007 8:08 pm
by Scott
When calibrating a map with "Known Points (skewed)", the map does not need to be perfectly "North Up". As long as the top of the map is within 45 degrees of north, then it can be calibrated correctly. If you need to rotate it, you can use any graphics imaging program, or even Windows Explorer to rotate the map in 90 degree increments until North is somewhat facing up.

Posted: Wed Mar 21, 2007 9:15 pm
by msjfb
That's great, thanks.
Is 3 points really enough : I was thinking of using 4 points (one near each corner) ^

Frank

Posted: Wed Mar 21, 2007 10:24 pm
by Scott
The more points the better, as long as they are accurate. 3 will do if there is no curvature to the map.

Posted: Wed Mar 21, 2007 10:25 pm
by Scott
Also, the further apart the points are, the more accurate the map calibration will be.

Posted: Wed Mar 21, 2007 10:35 pm
by msjfb
Your input is much appreciated. Thanks.