NavList:

   

Reply

Bill wrote:
>
> So it looks like it is calculating ellipsoidal, but not as well as Paul's
> unit. (2229 on mine vs. 2232 on Paul's in his example)  Perhaps time for a
> firmware update?

You may be confused on this point, Bill -- my Magellan 315 does *not*
compute distance on the ellipsoid. It uses a sphere. That's how I'm
able to do spherical trig on it.

A couple people on another discussion group tested their receivers for
me. The eMap uses an ellipsoid, a Lowrance model uses a sphere.

The test I asked them to run was to enter 3 waypoints, all on the same
longitude. Put P1 at the Equator, P2 at 40N, P3 at 80N. Create a route
from P1 to P2 to P3. If both legs are the same length, the device is
computing on a sphere. The Magellan 315 says both legs are exactly
2400 miles.

When I first discovered that, I was a bit disappointed. But now I
think it was perfectly reasonable for Magellan to simplify the
computation to a sphere. At long distance, a few km one way or the
other doesn't matter to me. The important thing is that the
approximation converges on the precise value as I get close to the
destination.

   

Reply