| Subject: | corrected a miscalculation of auto precision |
Hi.
It seems that there are some errors in auto precision calculation,
especially in how to handle integers.
I tried to fix it. Check out the patch attached or see following github
branch.
http://github.com/hiratara/Geo-Hash/tree/fix-precision
| Subject: | fix-precision.patch |
diff --git a/lib/Geo/Hash.pm b/lib/Geo/Hash.pm
index 5093df7..1604edf 100644
--- a/lib/Geo/Hash.pm
+++ b/lib/Geo/Hash.pm
@@ -2,6 +2,7 @@ package Geo::Hash;
use warnings;
use strict;
+use POSIX qw/ceil/;
use Carp;
=head1 NAME
@@ -58,14 +59,23 @@ sub _mid {
return ( $ar->[$wh][0] + $ar->[$wh][1] ) / 2;
}
-# The number of bits necessary to represent the specified number of
-# decimal digits
-sub _d2b { int( shift() * 3.32192809488736 + 1 ) }
-
-sub _bits_for_number {
+sub _num_of_decimal_places($) {
my $n = shift;
return 0 unless $n =~ s/.*\.//;
- return _d2b( length $n );
+ return length $n;
+}
+
+sub _length_for_bits($$) {
+ my ($bits, $is_lat) = @_;
+ my $q = int($bits / 5);
+ my $r = $bits % 5;
+ if ($r == 0) {
+ return $q * 2;
+ } elsif ($r <= ($is_lat ? 2 : 3)) {
+ return $q * 2 + 1;
+ } else {
+ return $q * 2 + 2;
+ }
}
=head2 C<< precision >>
@@ -77,11 +87,16 @@ lat, lon pair.
=cut
+use constant LOG2_10 => log(10) / log(2);
+use constant LOG2_180 => log(180) / log(2);
+use constant LOG2_360 => log(360) / log(2);
sub precision {
my ( $self, $lat, $lon ) = @_;
- my $lab = _bits_for_number( $lat ) + 8;
- my $lob = _bits_for_number( $lon ) + 9;
- return int( ( ( $lab > $lob ? $lab : $lob ) + 1 ) / 2.5 );
+ my $lab = ceil(_num_of_decimal_places($lat) * LOG2_10 + LOG2_180);
+ my $lob = ceil(_num_of_decimal_places($lon) * LOG2_10 + LOG2_360);
+ my $la_len = _length_for_bits($lab, 1);
+ my $lo_len = _length_for_bits($lob, 0);
+ return $la_len > $lo_len ? $la_len : $lo_len;
}
=head2 C<< encode >>
diff --git a/t/precision.t b/t/precision.t
new file mode 100644
index 0000000..15cac8c
--- /dev/null
+++ b/t/precision.t
@@ -0,0 +1,17 @@
+use strict;
+use warnings;
+use Test::More;
+use Geo::Hash;
+
+my $gh = Geo::Hash->new;
+is $gh->precision('45', '-120'), 4;
+is $gh->precision('45.0', '-120'), 5;
+is $gh->precision('45', '-120.0'), 5;
+is $gh->precision('45.00', '-120'), 6;
+is $gh->precision('45', '-120.00'), 7;
+is $gh->precision('45.000', '-120'), 8;
+is $gh->precision('45', '-120.000'), 8;
+is $gh->precision('45.00000', '-120'), 10;
+is $gh->precision('45', '-120.00000'), 11;
+
+done_testing;