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Normalize geometry structure; classify polygon rings #33

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8a8f615
Normalize geometry structure; classify polygon rings
jfirebaugh Oct 9, 2015
e4ec4c6
fix ring classification
mourner Mar 16, 2016
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8 changes: 8 additions & 0 deletions CHANGELOG.md
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@@ -1,5 +1,13 @@
## vector-tile-js changelog

### 2.0.0 (in progress)

- The structure of the return value of `loadGeometry()` was normalized. For point features, `loadGeometry()` now returns
an array of points. For polygon features, `loadGeometry()` now classifies rings and groups them into outer and inner
rings, using an extra level of array nesting. I.e., the return value for polygons is an array of arrays of arrays of
Points. The structure for line features (array of arrays of points) is unchanged.
- `toGeoJSON()` now classifies polygons into `Polygon` and `MultiPolygon` types based on ring structure.

### 1.2.0 (2015-12-10)

- Added "id" property to toGeoJSON() output
Expand Down
6 changes: 4 additions & 2 deletions README.md
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Expand Up @@ -97,7 +97,9 @@ An object that contains the data for a single feature.

#### Methods

- **loadGeometry()** — parses feature geometry and returns an array of
[Point](https://github.com/mapbox/point-geometry) arrays (with each point having `x` and `y` properties)
- **loadGeometry()** — returns feature geometry. Since the vector tile specification does not distinguish between Point and MultiPoint, LineString and MultiLineString, or Polygon and MultiPolygon, the result is always treated as a "Multi" variant:
- For point features, the return value is an array of [`Point`](https://github.com/mapbox/point-geometry)s.
- For line features, it is an array of arrays of `Point`s.
- For polygon features, it is an array of arrays of arrays of `Point`s.
- **bbox()** — calculates and returns the bounding box of the feature in the form `[x1, y1, x2, y2]`
- **toGeoJSON(x, y, z)** — returns a GeoJSON representation of the feature. (`x`, `y`, and `z` refer to the containing tile's index.)
131 changes: 129 additions & 2 deletions fixtures.js
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Expand Up @@ -2,7 +2,7 @@ var mapnik = require('mapnik');
var path = require('path');
var fs = require('fs');

mapnik.register_datasource(path.join(mapnik.settings.paths.input_plugins,'geojson.input'));
mapnik.register_datasource(path.join(mapnik.settings.paths.input_plugins, 'geojson.input'));

var fixtures = {
"zero-point": {
Expand Down Expand Up @@ -31,6 +31,19 @@ var fixtures = {
}
]
},
"zero-polygon": {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"geometry": {
"type": "MultiPolygon",
"coordinates": []
},
"properties": {}
}
]
},
"singleton-multi-point": {
"type": "FeatureCollection",
"features": [
Expand All @@ -57,6 +70,19 @@ var fixtures = {
}
]
},
"singleton-multi-polygon": {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"geometry": {
"type": "MultiPolygon",
"coordinates": [[[[0, 0], [1, 0], [1, 1], [0, 0]]]]
},
"properties": {}
}
]
},
"multi-point": {
"type": "FeatureCollection",
"features": [
Expand All @@ -82,11 +108,112 @@ var fixtures = {
"properties": {}
}
]
},
"multi-polygon": {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"geometry": {
"type": "MultiPolygon",
"coordinates": [[[[0, 0], [1, 0], [1, 1], [0, 0]]], [[[0, 0], [-1, 0], [-1, -1], [0, 0]]]]
},
"properties": {}
}
]
},
"polygon-with-inner": {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"geometry": {
"type": "Polygon",
"coordinates": [[[-2, 2], [2, 2], [2, -2], [-2, -2], [-2, 2]], [[-1, 1], [1, 1], [1, -1], [-1, -1], [-1, 1]]]
},
"properties": {}
}
]
},
"multipolygon": {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"properties": {},
"geometry": {
"type": "MultiPolygon",
"coordinates": [
[
[
[
-65.91796875,
-23.40276490540795
],
[
-65.91796875,
8.407168163601076
],
[
-35.859375,
8.407168163601076
],
[
-35.859375,
-23.40276490540795
],
[
-65.91796875,
-23.40276490540795
]
]
],
[
[
[
-9.84375,
12.897489183755892
],
[
-9.84375,
37.16031654673677
],
[
18.28125,
37.16031654673677
],
[
18.28125,
12.897489183755892
],
[
-9.84375,
12.897489183755892
]
]
]
]
}
}
]
},
"stacked-multipolygon": {
"type": "FeatureCollection",
"features": [
{
"type": "Feature",
"geometry": {
"type": "MultiPolygon",
"coordinates": [[[[-2, 2], [2, 2], [2, -2], [-2, -2], [-2, 2]]], [[[-1, 1], [1, 1], [1, -1], [-1, -1], [-1, 1]]]]
},
"properties": {}
}
]
}
}

for (var fixture in fixtures) {
var vtile = new mapnik.VectorTile(0,0,0);
var vtile = new mapnik.VectorTile(0, 0, 0);
vtile.addGeoJSON(JSON.stringify(fixtures[fixture]), "geojson");
fs.writeFileSync('./test/fixtures/' + fixture + '.pbf', vtile.getData());
}
108 changes: 86 additions & 22 deletions lib/vectortilefeature.js
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Expand Up @@ -47,8 +47,8 @@ VectorTileFeature.prototype.loadGeometry = function() {
length = 0,
x = 0,
y = 0,
lines = [],
line;
line = [],
lines = [line];

while (pbf.pos < end) {
if (!length) {
Expand All @@ -59,21 +59,23 @@ VectorTileFeature.prototype.loadGeometry = function() {

length--;

if (cmd === 1 || cmd === 2) {
if (cmd === 2 || (cmd === 1 && this.type === 1)) { // MLLLC
x += pbf.readSVarint();
y += pbf.readSVarint();
line.push(new Point(x, y));

if (cmd === 1) { // moveTo
if (line) lines.push(line);
} else if (cmd === 1) {
x += pbf.readSVarint();
y += pbf.readSVarint();
if (line.length) {
line = [];
lines.push(line);
}

line.push(new Point(x, y));

} else if (cmd === 7) {

// Workaround for https://github.com/mapbox/mapnik-vector-tile/issues/90
if (line) {
if (line.length) {
line.push(line[0].clone()); // closePolygon
}

Expand All @@ -82,9 +84,16 @@ VectorTileFeature.prototype.loadGeometry = function() {
}
}

if (line) lines.push(line);

return lines;
switch (this.type) {
case 1:
return line;
case 2:
return lines;
case 3:
return classifyRings(lines);
default:
throw new Error('Unknown vector tile feature type: ' + this.type);
}
};

VectorTileFeature.prototype.bbox = function() {
Expand Down Expand Up @@ -131,10 +140,10 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
x0 = this.extent * x,
y0 = this.extent * y,
coords = this.loadGeometry(),
type = VectorTileFeature.types[this.type];
type = VectorTileFeature.types[this.type],
i, j;

for (var i = 0; i < coords.length; i++) {
var line = coords[i];
function project(line) {
for (var j = 0; j < line.length; j++) {
var p = line[j], y2 = 180 - (p.y + y0) * 360 / size;
line[j] = [
Expand All @@ -144,15 +153,30 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {
}
}

if (type === 'Point' && coords.length === 1) {
coords = coords[0][0];
} else if (type === 'Point') {
coords = coords[0];
type = 'MultiPoint';
} else if (type === 'LineString' && coords.length === 1) {
switch (this.type) {
case 1:
project(coords);
break;

case 2:
for (i = 0; i < coords.length; i++) {
project(coords[i]);
}
break;

case 3:
for (i = 0; i < coords.length; i++) {
for (j = 0; j < coords[i].length; j++) {
project(coords[i][j]);
}
}
break;
}

if (coords.length === 1) {
coords = coords[0];
} else if (type === 'LineString') {
type = 'MultiLineString';
} else {
type = 'Multi' + type;
}

var result = {
Expand All @@ -170,3 +194,43 @@ VectorTileFeature.prototype.toGeoJSON = function(x, y, z) {

return result;
};

// classifies an array of rings into polygons with outer rings and holes

function classifyRings(rings) {
var len = rings.length;

if (len <= 1) return [rings];

var polygons = [],
polygon,
ccw;

for (var i = 0; i < len; i++) {
var area = signedArea(rings[i]);
if (area === 0) continue;

if (ccw === undefined) ccw = area < 0;

if (ccw === area < 0) {
if (polygon) polygons.push(polygon);
polygon = [rings[i]];

} else {
polygon.push(rings[i]);
}
}
if (polygon) polygons.push(polygon);

return polygons;
}

function signedArea(ring) {
var sum = 0;
for (var i = 0, len = ring.length, j = len - 1, p1, p2; i < len; j = i++) {
p1 = ring[i];
p2 = ring[j];
sum += (p2.x - p1.x) * (p1.y + p2.y);
}
return sum;
}
2 changes: 1 addition & 1 deletion package.json
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Expand Up @@ -12,7 +12,7 @@
"benchmark": "^1.0.0",
"coveralls": "~2.11.2",
"istanbul": "~0.3.6",
"mapnik": "^3.1.6",
"mapnik": "^3.4.8",
"jshint": "^2.6.3",
"pbf": "^1.3.2",
"tape": "~3.5.0",
Expand Down
4 changes: 2 additions & 2 deletions test/fixtures/multi-point.pbf
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@@ -1,2 +1,2 @@

geojson" � � .-(� x

geojson"� �.-(� x
Expand Down
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