Simplification

Atelier SVG includes algorithms for reducing the number of points in a path while preserving its visual shape. This is useful for optimizing file size and improving rendering performance.

SimplifierInterface

All simplifiers implement Atelier\Svg\Path\Simplifier\SimplifierInterface:

public function simplify(Data $pathData, float $tolerance): Data;

The method returns a new Data object: the original is not modified. The $tolerance parameter controls how aggressively points are removed. A tolerance of zero returns the original path unchanged. Negative values throw InvalidArgumentException.

Non-line segments (curves, arcs, close commands) are preserved as-is. Only sequences of MoveTo + LineTo segments (polylines) are simplified.

Simplifier (Ramer-Douglas-Peucker)

Atelier\Svg\Path\Simplifier\Simplifier uses the Ramer-Douglas-Peucker algorithm. It recursively finds the point farthest from the line between the start and end, keeping it only if its perpendicular distance exceeds the tolerance.

The tolerance represents the maximum allowed perpendicular distance (in SVG user units) from a removed point to the simplified line.

use Atelier\Svg\Path\Simplifier\Simplifier;
use Atelier\Svg\Path\PathParser;

$parser = new PathParser();
$data = $parser->parse('M 0,0 L 1,0.1 L 2,0 L 3,0.1 L 4,0');

$simplifier = new Simplifier();
$simplified = $simplifier->simplify($data, tolerance: 0.2);

// Points within 0.2 units of the straight line are removed
echo $simplified; // "M 0,0 L 4,0"

Best suited for paths where preserving endpoints is important.

VisvalingamWhyattSimplifier

Atelier\Svg\Path\Simplifier\VisvalingamWhyattSimplifier uses the Visvalingam-Whyatt algorithm. It iteratively removes the point that forms the smallest triangle with its neighbors, stopping when all remaining triangles exceed the area tolerance.

The tolerance represents the minimum triangle area (in square SVG user units) that a point must contribute to be retained.

use Atelier\Svg\Path\Simplifier\VisvalingamWhyattSimplifier;

$simplifier = new VisvalingamWhyattSimplifier();
$simplified = $simplifier->simplify($data, tolerance: 5.0);

Tends to produce more visually pleasing results than RDP for cartographic and organic shapes.

CollinearPointRemover

Atelier\Svg\Path\Simplifier\CollinearPointRemover removes points that are nearly collinear with their neighbors. For each interior point, it computes the perpendicular distance to the line formed by the previous and next points. Points within tolerance are dropped.

use Atelier\Svg\Path\Simplifier\CollinearPointRemover;

$simplifier = new CollinearPointRemover();
$simplified = $simplifier->simplify($data, tolerance: 0.5);

This is the fastest of the three algorithms. Use it as a first pass to strip obviously redundant points before applying a more sophisticated simplifier.

Choosing a Tolerance

The right value depends on the scale of your coordinates and the level of detail required.

See also

• Path data model: Data, segments, parser
• Path analysis: measure paths before and after simplification
• Optimization: broader optimization strategies