[Manifold-l] Bearing(I)

[Colin Driscoll]

Peter,

It sounds like you are using the most recent 7x release (7.1.1.279) so see
this thread on Georeference

 http://69.17.46.171/Site/Thread.aspx?id=27048&ti=632931194554830000

To get sense from Bearing (I) you will need to reinstall the previous
release (7.1.0.138) which I was lucky enough to have on my laptop.

Cheers

Colin



-----Original Message-----
From: manifold-l-bounces at lists.directionsmag.com
[mailto:manifold-l-bounces at lists.directionsmag.com] On Behalf Of Peter
Ronning
Sent: Saturday, 9 September 2006 9:32 AM
To: manifold-l at lists.directionsmag.com
Subject: [Manifold-l] Bearing(I)

I recently laid out several lines, with known lengths and bearings, in a 2D
CAD program, saved the lines in a DXF, and imported the dxf into Manifold as
a drawing.  I assigned the drawing a UTM Zone 9 projection.  The location is
at about 57 degrees north latitude.

Once I had the drawing in Manifold, I checked the bearings of the lines by
looking at their intrinsic field, Bearing(I).  I know enough about
projections that I didn't expect the bearings in Manifold to be exactly the
same as the bearings in the dxf file.  However, the differences are
startling.  For example, a line that is at 60 deg in the dxf file has a
Bearing(I) of 47.666 deg.

The visual representation of the line on the Manifold screen looks like a 60
degree line, not a 48 degree line.

In the help file it states that the bearing is computed using ellipsoidal
geometry, with east at 90 degrees and west at 270 degrees.  Given that, and
the projection issues, I would not have expected the Bearing(I) to be 60,
but I would have expected it to be perhaps within a couple of degrees of 60.

Does the 47.666 seem reasonable to those more knowledgeable than I?

_________________________________________
Peter A. Ronning, P.Eng.
New Caledonian Geological Consulting
Phone (604) 684-6864  FAX (604) 608-2957
email: peter at ronning.ca

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