[Proj] Finally: geodesic-1.0 is available

Charles Karney ckarney at sarnoff.com
Thu Jan 8 17:10:07 EST 2009

>> I find the mini command language within the program (as opposed to
>> a complex set of commandline options) an odd approach.
> I do not find it too odd.  For example, I use gp to compute the
> constants and what all and it is often used in the same manner.  Even
> maxima.  The difference is that I do not evaluate math or complex
> expressions.  ...

I note that the following "works":

 echo "earth ellps=WGS84; p1 10 20; p2 30 40" | ./geodesic -n

so that geodesic can be used as part of a pipe.  A slight complication
is that the output comes in multi-line form which will typically need to
be decoded.  In this way tabular data can be fed into the tool and
tabular results can be generated.

If you did want to facilitate this mode of usage, then I would suggest
something like

(1) ellipse can be specified on command line
(2) flag -f to specify forward calc
    input line = lon1 lat1 dist azi1
    output line = lon2 lat2 azi2
(3) flag -r to specify reverse calc
    input line = lon1 lat1 lon2 lat2
    output line = dist azi1 azi2

A few other comments:

(1) Decimal degrees are nice (especially in a pipe).  How do I get them?

(2) Prec changes the precision of lat/lon angles but not azimuths.

(3) How is the "height" used?  It doesn't seem to affect the results.

(4) No word on the accuracy?  For Vincenty, I've read 1 mm except for
near antipodal in which case don't believe the results.  Does this apply

On the last point:

Does anyone know of a large set of test data?  The papers on the
geodesic paper typically present a handful of cases.  Instead I'm
thinking of a large test set mostly with randomly chosen points but with
some significant fraction of "hard" examples (near antipodal, points
near the poles, etc.).  I'm thinking that these could be produced by
doing the forward calculation to high precision (using as many terms in
the expansion of the integral to get to 1 nm precision or better on the
WGS84 ellipsoid).  The result data could be used to test both forward
and reverse geodesic calculations.

Charles Karney <ckarney at sarnoff.com>
Sarnoff Corporation, Princeton, NJ 08543-5300

URL: http://charles.karney.info
Tel: +1 609 734 2312
Fax: +1 609 734 2662

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