function legacy_gmap_polyutil_dp_encode in GMap Module 7.2
Implementation of the Douglas-Peucker polyline simplification algorithm.
See: http://facstaff.unca.edu/mcmcclur/GoogleMaps/EncodePolyline/algorithm.html
Parameters
array $points: An array of coordinate pairs.
Return value
array An array of keys => weights; the keys correspond with indices of points in the $points array. Some points may be insignificant according to the algorithm--they will not have entries in the return array. The "weights" are actually the point's distance from the line segment that it subdivides.
1 call to legacy_gmap_polyutil_dp_encode()
- legacy_gmap_polyutil_polyline in tests/
inc/ gmap_polyutil.inc - Simplify a set of points and generate an "Encoded Polyline" for Google Maps.
File
- tests/
inc/ gmap_polyutil.inc, line 132 - Encoded polyline utilities.
Namespace
tests\incCode
function legacy_gmap_polyutil_dp_encode($points) {
$weights = array();
if (count($points) > 2) {
// The 'stack' holds line segments to be simplified.
$stack[] = array(
0,
count($points) - 1,
);
while (count($stack) > 0) {
// Take a line segment to look at.
$segment = array_pop($stack);
// Figure out which subdividing point
// is the furthest off the line segment.
$max_dist = 0;
for ($i = $segment[0] + 1; $i < $segment[1]; $i++) {
$dist = legacy_gmap_polyutil_point_line_dist($points[$i], $points[$segment[0]], $points[$segment[1]]);
if ($dist > $max_dist) {
$max_dist = $dist;
$max_i = $i;
}
}
// If the subdividing point found above
// is significantly off the line
// segment then we want to simplify further.
// Add sub-segments to the stack.
if ($max_dist > GMAP_DP_EPSILON) {
$weights[$max_i] = $max_dist;
array_push($stack, array(
$segment[0],
$max_i,
));
array_push($stack, array(
$max_i,
$segment[1],
));
}
}
}
// The first and last points of the line should always be visible.
$levels = legacy__gmap_polyutil_zoom_levels();
$weights[0] = $levels[0];
$weights[count($points) - 1] = $levels[0];
return $weights;
}