Re: [Geographiclib-users] Find S12 using planimeter

[Charles K. <cha...@sr...>]

On 2014-09-25 09:01, Mike Toews wrote:
> I'm unable to build a higher precision version. On Debian Wheezy, I
> can't compile with either GEOGRAPHICLIB_PRECISION 4 or 5, since the
> supported releases of Boost 1.49 or MPFR 3.1.0 don't meet the
> requirements for v 1.37 of GeographicLib, which requires either Boost
> 1.54 or MPFR 3.5.9 (in CMakeLists.txt). So I'll test this out some
> other time.
>

You've got the MPFR requirements wrong...

I'm using 3.1.2 but I would expect 3.1.0 to be OK too.  The 3.5.9 refers
to MPFR C++ which is a single header file (mpreal.h) you can stick into
the include directory.  The MPFR C++ download link is

   http://www.holoborodko.com/pavel/mpfr/#download

I will fix the documentation in CMakeLists.txt and in doxygen to clarify
this.

By the way, at some point as you increase the precision you need to
switch to using Planimeter with the -E option.  The geodesics are then
computed with elliptic integrals.  The area calculation uses a 30th
order series (I never figured out how to express the are integral in
terms of elliptic integrals); so eventually you will run out of accuracy
on areas (but it's probably good for at least 1000 digits for WGS84).

   --Charles