---
title: Triangle
description: Definition, illustrated examples and supported representations of Triangle in Spatial Types 1.x.
canonical_html: ./triangle.html
canonical_markdown: ./triangle.md
---

[View HTML version](./triangle.html)

> **Next version** — This documentation describes a major version that is not yet the current stable release of `spatial-types`.
> [View the library roadmap](../../index.md)

## What is a Triangle?

A valid Triangle is a Polygon with three distinct vertices and no holes. Its single exterior ring returns to its starting point, so the ring contains four
positions.

Spatial Types can also store an incomplete or open triangle boundary, or additional rings, without enforcing these geometric rules.
Use explicit [geometric validation](../validators.md) to check the represented triangle.

![Two triangles with three vertices each. Each exterior ring closes by repeating its first position.](../../../assets/images/spatial-types/types/triangle.svg)

## Triangle — Supported representations

Availability in the current version of Spatial Types:

| Coordinate layout | Geometry Mutable | Geometry Immutable | Geography Mutable | Geography Immutable |
| ----------------- | :--------------: | :----------------: | :---------------: | :-----------------: |
| XY                |         ✅        |          ✅         |         ✅         |          ✅          |
| XYZ               |         ✅        |          ✅         |         ✅         |          ✅          |
| XYM               |         ✅        |          ✅         |         ✅         |          ✅          |
| XYZM              |         ✅        |          ✅         |         ✅         |          ✅          |

## Creating the illustrated objects

The examples recreate the labelled objects above using Geometry in XY.
Composer’s autoloader must already be loaded. Variable names match the point letters in the illustration.

### Immutable objects

```php
<?php

use LongitudeOne\SpatialTypes\Types\Dimension2\Geometry\PointImmutable;
use LongitudeOne\SpatialTypes\Types\Dimension2\Geometry\LineStringImmutable;
use LongitudeOne\SpatialTypes\Types\Dimension2\Geometry\TriangleImmutable;

// Immutable objects must be fully initialized through their constructors.

$a = new PointImmutable(7, 6.5);
$b = new PointImmutable(28.5, 6.5);
$c = new PointImmutable(7, 20);
$d = new PointImmutable(43, 6.5);
$e = new PointImmutable(68.5, 9.5);
$f = new PointImmutable(55.5, 20.5);

$firstRing = new LineStringImmutable([$a, $b, $c, $a]);
$firstTriangle = new TriangleImmutable([$firstRing]);
$secondRing = new LineStringImmutable([$d, $e, $f, $d]);
$secondTriangle = new TriangleImmutable([$secondRing]);
```

### Mutable objects

```php
<?php

use LongitudeOne\SpatialTypes\Types\Dimension2\Point;
use LongitudeOne\SpatialTypes\Types\Dimension2\LineString;
use LongitudeOne\SpatialTypes\Types\Dimension2\Triangle;

$a = new Point(7, 6.5);
$b = new Point(28.5, 6.5);
$c = new Point(7, 20);
$d = new Point(43, 6.5);
$e = new Point(68.5, 9.5);
$f = new Point(55.5, 20.5);

$firstRing = new LineString([$a, $b, $c, $a]);
$firstTriangle = new Triangle([$firstRing]); // Using the constructor.
$secondRing = new LineString([$d, $e, $f, $d]);
// Starting empty and adding the exterior ring with a method.
$secondTriangle = new Triangle([])->addRing($secondRing);
```