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expose the area of the geometry as *geometry*.area #47

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expose the area of the geometry as *geometry*.area #47

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2 changes: 1 addition & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -87,7 +87,7 @@ The returned geometry objects are typically passed to [d3.geoPath](https://githu

<a name="contours_contour" href="#contours_contour">#</a> <i>contours</i>.<b>contour</b>(<i>values</i>, <i>threshold</i>) [<>](https://github.com/d3/d3-contour/blob/master/src/contours.js "Source")

Computes a single contour, returning a [GeoJSON](http://geojson.org/geojson-spec.html) [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon) [geometry object](http://geojson.org/geojson-spec.html#geometry-objects) representing the area where the input <i>values</i> are greater than or equal to the given [*threshold* value](#contours_thresholds); the threshold value for each geometry object is exposed as <i>geometry</i>.value.
Computes a single contour, returning a [GeoJSON](http://geojson.org/geojson-spec.html) [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon) [geometry object](http://geojson.org/geojson-spec.html#geometry-objects) representing the area where the input <i>values</i> are greater than or equal to the given [*threshold* value](#contours_thresholds); the threshold value for each geometry object is exposed as <i>geometry</i>.value, and its area exposed as <i>geometry</i>.area.

The input *values* must be an array of length <i>n</i>×<i>m</i> where [<i>n</i>, <i>m</i>] is the contour generator’s [size](#contours_size); furthermore, each <i>values</i>[<i>i</i> + <i>jn</i>] must represent the value at the position ⟨<i>i</i>, <i>j</i>⟩. See [*contours*](#_contours) for an example.

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8 changes: 6 additions & 2 deletions src/contours.js
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Expand Up @@ -52,12 +52,15 @@ export default function() {
// Based on https://github.com/mbostock/shapefile/blob/v0.6.2/shp/polygon.js
function contour(values, value) {
var polygons = [],
holes = [];
holes = [],
a = 0;

isorings(values, value, function(ring) {
smooth(ring, values, value);
if (area(ring) > 0) polygons.push([ring]);
var ar = area(ring);
if (ar > 0) polygons.push([ring]);
else holes.push(ring);
a += ar / 2;
});

holes.forEach(function(hole) {
Expand All @@ -72,6 +75,7 @@ export default function() {
return {
type: "MultiPolygon",
value: value,
area: a,
coordinates: polygons
};
}
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7 changes: 7 additions & 0 deletions test/contours-test.js
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Expand Up @@ -18,6 +18,7 @@ tape("contours(values) returns the expected result for an empty polygon", functi
{
"type": "MultiPolygon",
"value": 0.5,
"area": 0,
"coordinates": []
}
]);
Expand All @@ -41,6 +42,7 @@ tape("contours(values) returns the expected result for a simple polygon", functi
{
"type": "MultiPolygon",
"value": 0.5,
"area": 14.5,
"coordinates": [
[
[[6, 7.5], [6, 6.5], [6, 5.5], [6, 4.5], [6, 3.5], [5.5, 3], [4.5, 3],
Expand Down Expand Up @@ -69,6 +71,7 @@ tape("contours(values).contour(value) returns the expected result for a simple p
], 0.5), {
"type": "MultiPolygon",
"value": 0.5,
"area": 14.5,
"coordinates": [
[
[[6, 7.5], [6, 6.5], [6, 5.5], [6, 4.5], [6, 3.5], [5.5, 3], [4.5, 3],
Expand Down Expand Up @@ -97,6 +100,7 @@ tape("contours.smooth(false)(values) returns the expected result for a simple po
{
"type": "MultiPolygon",
"value": 0.5,
"area": 14.5,
"coordinates": [
[
[[6, 7.5], [6, 6.5], [6, 5.5], [6, 4.5], [6, 3.5], [5.5, 3], [4.5, 3],
Expand Down Expand Up @@ -126,6 +130,7 @@ tape("contours(values) returns the expected result for a polygon with a hole", f
{
"type": "MultiPolygon",
"value": 0.5,
"area": 12,
"coordinates": [
[
[[6, 7.5], [6, 6.5], [6, 5.5], [6, 4.5], [6, 3.5], [5.5, 3], [4.5, 3],
Expand Down Expand Up @@ -157,6 +162,7 @@ tape("contours(values) returns the expected result for a multipolygon", function
{
"type": "MultiPolygon",
"value": 0.5,
"area": 14,
"coordinates": [
[
[[5, 7.5], [5, 6.5], [5, 5.5], [5, 4.5], [5, 3.5], [4.5, 3], [3.5, 3],
Expand Down Expand Up @@ -190,6 +196,7 @@ tape("contours(values) returns the expected result for a multipolygon with holes
{
"type": "MultiPolygon",
"value": 0.5,
"area": 16,
"coordinates": [
[
[[4, 5.5], [4, 4.5], [4, 3.5], [3.5, 3], [2.5, 3], [1.5, 3], [1, 3.5],
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