/ 
Geo-Spline-0.16
River stage zero No dependents
/ Geo::Spline

NAME

Geo::Spline - Calculate geographic locations between GPS fixes.

SYNOPSIS

use Geo::Spline;
my $p0={time=>1160449100.67, #seconds
        lat=>39.197807,      #degrees
        lon=>-77.263510,     #degrees
        speed=>31.124,       #m/s
        heading=>144.8300};  #degrees clockwise from North
my $p1={time=>1160449225.66,
        lat=>39.167718,
        lon=>-77.242278,
        speed=>30.615,
        heading=>150.5300};
my $spline=Geo::Spline->new($p0, $p1);
my %point=$spline->point(1160449150);
print "Lat:", $point{"lat"}, ", Lon:", $point{"lon"}, "\n\n";

my @points=$spline->pointlist();
foreach (@points) {
  print "Lat:", $_->{"lat"}, ", Lon:", $_->{"lon"}, "\n";
}

DESCRIPTION

This program was developed to be able to calculate the position between two GPS fixes using a 2-dimensional 3rd order polynomial spline.

f(t)  = A + B(t-t0)  + C(t-t0)^2 + D(t-t0)^3 #position in X and Y
f'(t) = B + 2C(t-t0) + 3D(t-t0)^2            #velocity in X and Y

I did some simple Math (for an engineer with a math minor) to come up with these formulas to calculate the unknowns from our knowns.

A = x0                                     # when (t-t0)=0 in f(t)
B = v0                                     # when (t-t0)=0 in f'(t)
C = (x1-A-B(t1-t0)-D(t1-t0)^3)/(t1-t0)^2   # solve for C from f(t)
C = (v1-B-3D(t1-t0)^2)/2(t1-t0)            # solve for C from f'(t)
D = (v1(t1-t0)+B(t1-t0)-2x1+2A)/(t1-t0)^3  # equate C=C then solve for D

CONSTRUCTOR

new

my $spline=Geo::Spline->new($p0, $p1);

METHODS

ellipsoid

Method to set or retrieve the current ellipsoid object. The ellipsoid is a Geo::Ellipsoids object.

my $ellipsoid=$obj->ellipsoid;  #Default is WGS84

$obj->ellipsoid('Clarke 1866'); #Built in ellipsoids from Geo::Ellipsoids
$obj->ellipsoid({a=>1});        #Custom Sphere 1 unit radius

point

Method returns a single point from a single time.

my $point=$spline->point($t1);
my %point=$spline->point($t1);

pointlist

Method returns a list of points from a list of times.

my $list=$spline->pointlist($t1,$t2,$t3);
my @list=$spline->pointlist($t1,$t2,$t3);

timelist

Method returns a list of times (n+1). The default will return a list with an integer number of seconds between spline end points.

my $list=$spline->timelist($samples); 
my @list=$spline->timelist();

TODO

Integrate a better Lat, Lon to meter conversions.

BUGS

Please send to the geo-perl email list.

LIMITS

I use a very rough conversion from degrees to meters and then back. It is accurate for short distances.

AUTHOR

Michael R. Davis qw/perl michaelrdavis com/

LICENSE

Copyright (c) 2006 Michael R. Davis (mrdvt92)

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SEE ALSO

http://search.cpan.org/src/MRDVT/Geo-Spline-0.16/doc/spline.xls http://search.cpan.org/src/MRDVT/Geo-Spline-0.16/doc/spline.png Math::Spline Geo::Ellipsoids