[boost] [geometry] distance on multiline with spherical coordinates

Subject: [boost] [geometry] distance on multiline with spherical coordinates
From: Karsten Ahnert (karsten.ahnert_at_[hidden])
Date: 2012-06-25 14:39:35

Hi,

the following code produces some strange results:

typedef cs::spherical_equatorial< boost::geometry::degree > cs_type;
typedef model::point< double , 2, cs_type > point_type;
typedef model::linestring< point_type > linestring_type;

point_type p( 1.0 , 1.0 );
linestring_type l;
l.push_back( point_type( 0.0 , 2.0 ) );
l.push_back( point_type( 2.0 , 2.0 ) );
l.push_back( point_type( 4.0 , 2.0 ) );

cout << "Distance : " << boost::geometry::distance( p , l ) << endl;

for( size_t i=1 ; i<l.size() ; ++i )
{
    linestring_type l_tmp;
    l_tmp.push_back( l[i-1] );
    l_tmp.push_back( l[i] );
    cout << "Point distance : " << boost::geometry::distance( p , l_tmp
) << endl;
}

The output is

Distance : 0.0174373

Point distance : 0.0174586
Point distance : 0.0174373

This looks like a bug. The distance to the second segment can not be
smaller than that to the first one. If I change the coordinate system to
cartesian coordinates everything works as expected. Do I miss some major
points?