Geo-Index
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float sin_lat_diff_over_2 = sinf( ( lat_0 - f_lat_1 ) / 2.0 );float sin_lon_diff_over_2 = sinf( ( lon_0 - f_lon_1 ) / 2.0 );float n = ( sin_lat_diff_over_2 * sin_lat_diff_over_2 )+ (( sin_lon_diff_over_2 * sin_lon_diff_over_2 )* f_cos_lat_1* cosf( lat_0 ));/* The haversine formula may get messyaroundantipodal points so clip to the largest sane value. */if( n < 0.0 ) { n = 0.0; }returnf_diameter * asinf( sqrtf(n) );}/* Functions using doubles */double d_diameter, d_lat_1, d_lon_1;
double sin_lat_diff_over_2 =sin( ( lat_0 - d_lat_1 ) / 2.0 );double sin_lon_diff_over_2 =sin( ( lon_0 - d_lon_1 ) / 2.0 );double n = ( sin_lat_diff_over_2 * sin_lat_diff_over_2 )+ (( sin_lon_diff_over_2 * sin_lon_diff_over_2 )* d_cos_lat_1*cos( lat_0 ));/* The haversine formula may get messyaroundantipodal points so clip to the largest sane value. */if( n < 0.0 ) { n = 0.0; }returnd_diameter * asin(sqrt(n) );}/* End of C code */MODULE = Geo::Index PACKAGE = Geo::IndexPROTOTYPES: DISABLE
lib/Geo/Index.pm view on Meta::CPAN
($closest) =$index->Closest( [ -80, 20 ] );"$$closest{name}\n";# Also prints 'South Pole'($closest) =$index->Closest($points[1], {post_condition=>'NONE'} );"$$closest{name}\n";# Also prints 'South Pole'($farthest) =$index->Farthest( [ 90, 0 ] );"$$farthest{name}\n";# Also prints 'South Pole'# Compute distance in meters between two points (using haversine formula)$m=$index->Distance( {lat=>51.507222,lon=>-0.1275 }, [ -6.2, 106.816667 ] );printf("London to Jakarta: %i km\n",$m/ 1000);$index->DistanceFrom( [ 90, 0 ] );$m=$index->DistanceTo($points[1] );printf("Pole to pole: %i km\n",$m/ 1000);=head1 DESCRIPTION
lib/Geo/Index.pm view on Meta::CPAN
B<C<lon_rad>> - The point's longitude in radians [ -pi .. pi )=item *B<C<circumference>> - Circumference (in meters) of the circle of latitudethat the point falls on. This is computed from the body's equatorialcircumference assuming a spherical (not an oblate) body.=item *B<C<search_result_distance>> - Distance (in meters) of point from searchpoint of previous search. The distance computation assumes a spherical bodyand is computed using a ruggedized version of the haversine formula. Thisvalue is only generated when C<L<Search(...)|/Search( ... )>> is called with the C<radius>or C<sort_results> option. See also C<L<Distance(...)|/Distance( ... )>>, C<L<DistanceFrom(...)|/DistanceFrom( ... )>>,and C<L<DistanceTo(...)|/DistanceTo( ... )>>.=item *B<C<antipode_distance>> - Distance (in meters) of point from searchpoint's antipode as determined by a previous call to C<L<Farthest(...)|/Farthest( ... )>>.This distance is computed using a ruggedized version of the haversine formula.=backAs a convenience, most methods allow points to be specified using a shorthandnotation S<C<[ I<lat>, I<lon> ]>> or S<C<[ I<lat>, I<lon>, I<data> ]>>. Pointsgiven in this notation will be converted to hash-based points. If a pointcreated using this notation is returned as a search result it will be as areference to the hash constructed by Geo::Index and not as a reference to theoriginal array. To access the data field of a point created using the shorthandnotation use C<$$point{'data'}> where C<$point> is a search result point.
lib/Geo/Index.pm view on Meta::CPAN
$$p1{lat_rad} = Math::Trig::deg2rad($$p1{lat})unless($$p1{lat_rad});$$p1{lon_rad} = Math::Trig::deg2rad($$p1{lon})unless($$p1{lon_rad});returnHaversineDistance($$p1{lat_rad},$$p1{lon_rad});}#. Distance functions#.#. Geo::Index uses the haversine formula to compute great circle distances#. between points.#.#. Three versions are supported: a fallback version written in Perl (used if the#. C versions fail to compile) and two accelerated versions written in C, one#. using floats and the other using doubles. By default the C float version is#. used; if it fails to compile then the Perl version is used. Use of a specific#. version can also be requested with Geo::Index->SetDistanceFunctionType(...).#.#. The Perl version uses doubles. When using floats instead of doubles the loss#. of precision is typically under a meter (about 2 meters in the worst case).
lib/Geo/Index.pm view on Meta::CPAN
my$sin_lat_diff_over_2=sin( ($lat_0-$DistanceFrom_lat_1) / 2.0 );my$sin_lon_diff_over_2=sin( ($lon_0-$DistanceFrom_lon_1) / 2.0 );my$n= ($sin_lat_diff_over_2*$sin_lat_diff_over_2)+ (($sin_lon_diff_over_2*$sin_lon_diff_over_2)*$DistanceFrom_cos_lat_1*cos($lat_0));#. The haversine formula may get messy around antipodal points so clip to the largest sane value.if($n< 0.0 ) {$n= 0.0; }return$DistanceFrom_diameter* asin(sqrt($n) );}=head2 GetConfiguration( )
lib/Geo/Index.pm view on Meta::CPAN
This could be encountered in a number of ways. For example, a search using acondition function that itself runs a search against the secondindexcould beproblematic. This could be encountered evenwhenusing a singleindex. Forexample,ifcode relies on the distancesvaluesfrom a search it should save acopy of thembeforerunning subsearches against the same set of points. If thisis not done then the distancevaluesfrom the first search may be overwritten bythose of the subsequent searches.=item *Geo::Index uses the spherical haversine formula to compute distances. Whilequite fast, its accuracy over long distances is poor, with a worst case errorof about 0.1% (22 km). Since the module already has provision for changing thebackends used for the distance methods, adding a new backend to, for example,compute accurate distances on e.g. a WGS-84 spheroid would be simple andstraight-forward.=item *In places the code can be repetitious or awkward in style. This was donebecause, especially in the inner loops, speed has been favoured over clarity.
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