[OSRS-PROJ] Radius parameters

[Gerald I. Evenden]

Radius parameters such as R_A only apply when using projections in their
spherical form.  R_A is probably the most useful as it give the radius of a
sphere with the same surface area as the ellipsoid selected.  Also, it is
necessary
to select a ellipsoid when using R_A even though the projection is in the
spherical mode.

Snyder often uses a radius in his manual that is the R_A for Clarke 1866.

The other radius parameters have limited usage for sophisticates. ;-)

__________________________________________________
Jerry Evenden and the Low Riders, Katie and  Daisy May
gevenden at capecod.net  http://www.capecod.net/~gevenden
----- Original Message -----
From: Black, Jerry <BlackJ at mar.dfo-mpo.gc.ca>
To: <osrs-proj at remotesensing.org>
Sent: Monday, October 02, 2000 12:52 PM
Subject: [OSRS-PROJ] Radius parameters


> Hi,
>
> I hope this is not too off-topic... I'm using the proj4 library in my own
> application (on a win95 pc), and while it appears to work relatively well,
> I'm limited by my lack of understanding.
>
> In particular, I don't understand the significance of the Radius
Parameters
> as described in Evenden's reports. While the effect of choosing a given
> radius parameter is documented (e.g. R_A), what I'm lacking the rational
for
> choosing one of these parameters (or not), when choosing a given
projection.
>
>
> Is the choice merely up to the user (and therefore likely selected on some
> particular minimization of distortion), or are there well-known common
> practices (e.g. for a MERC projection of the Cdn east coast always use
R_A).
>
> Thanks in advance,

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