added perimeter

DanielJDufour · Aug 22, 2021 · 572278c · 572278c
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diff --git a/docs/PROPERTIES.md b/docs/PROPERTIES.md
@@ -12,6 +12,7 @@ Once you've created a GeoExtent, you will have access to the following propertie
 | height | 121 | The height of the extent in units of the [srs](https://en.wikipedia.org/wiki/Spatial_reference_system).  This is often either degrees latitude or meters. |
 | width | 93 | The width of the extent in units of the [srs](https://en.wikipedia.org/wiki/Spatial_reference_system).  This is often either degrees longitude or meters. |
 | area | 11253 | The area of the extent in units of the [srs](https://en.wikipedia.org/wiki/Spatial_reference_system). This is often in degrees or meters squared. Because this uses the units of the srs, this is just an approximation and can't be relied upon as the "true" area. |
+| perimeter | 428 | The perimeter of the extent in units of the [srs](https://en.wikipedia.org/wiki/Spatial_reference_system). This is often in degrees or meters. Because this uses the units of the srs, this is just an approximation and can't be relied upon as the "true" perimeter.
 | center | { x: -25.5, y: 13.5 } | The center of the extent or half-way point along the x and y directions. |
 | bottomLeft | { x: -72, y: -47 } | The bottom-left corner of the extent |
 | bottomRight | { x: 21, y: -47 } | The bottom-right corner of the extent |

diff --git a/geo-extent.js b/geo-extent.js
@@ -157,6 +157,7 @@ export class GeoExtent {
     ];
 
     this.area = this.width * this.height;
+    this.perimeter = 2 * this.width + 2 * this.height;
     this.bbox = [xmin, ymin, xmax, ymax];
     this.center = { x: avg(xmin, xmax), y: avg(ymin, ymax) };
     this.str = this.bbox.join(",");

diff --git a/test/test.mjs b/test/test.mjs
@@ -20,6 +20,7 @@ const NORTH_WEST_QUARTER_SPHERE = [-180, 0, 0, 90];
 const AS_OBJ_RESULT = {
   srs: 'EPSG:4326',
   area: AREA,
+  perimeter: 2 * WIDTH + 2 * HEIGHT,
   bbox: BBOX,
   center: CENTER,
   xmin: XMIN,
@@ -65,6 +66,7 @@ test("create from points", ({ eq }) => {
     topLeft: { x: 147, y: -18 },
     topRight: { x: 147, y: -18 },
     area: 0,
+    perimeter: 0,
     bbox: [ 147, -18, 147, -18 ],
     center: { x: 147, y: -18 },
     str: '147,-18,147,-18',