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flip-intersect line cover algo first pass
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@morganherlocker
morganherlocker committed Nov 4, 2014
1 parent 2d2a5d5 commit 10f1843
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Showing 14 changed files with 60,132 additions and 210,846 deletions.
101 changes: 72 additions & 29 deletions index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -58,7 +58,7 @@ function getLocked (geom, limits) {
}
locked = hashToArray(tileHash);
} else {
throw new Error('Geoemtry type not implemented')
throw new Error('Geoemtry type not implemented');
}
if(limits.min_zoom !== limits.max_zoom){
locked = mergeTiles(locked, limits);
Expand Down Expand Up @@ -206,7 +206,7 @@ function isLocalMin(i, segments) {

while (next && current[1][1] === next[1][1]) {
seek++;
next = segments[i+seek]
next = segments[i+seek];
}

// No next segment.
Expand All @@ -228,7 +228,7 @@ function isLocalMax(i, segments) {

while (next && current[1][1] === next[1][1]) {
seek++;
next = segments[i+seek]
next = segments[i+seek];
}

// No next segment.
Expand All @@ -241,6 +241,7 @@ function isLocalMax(i, segments) {
}

// modified from http://jsfiddle.net/justin_c_rounds/Gd2S2/light/
// line1 is an infinite line, and line2 is a finite segment
function lineIntersects(line1StartX, line1StartY, line1EndX, line1EndY, line2StartX, line2StartY, line2EndX, line2EndY, localMinMax) {
var denominator,
a,
Expand Down Expand Up @@ -286,14 +287,15 @@ function lineCover(coordinates, max_zoom) {
var segments = [];
for(var i = 0; i < coordinates.length - 1; i++) {
var iNext = i+1;
segments.push([[coordinates[i][0], coordinates[i][1]], [coordinates[iNext][0], coordinates[iNext][1]]]);
// add endpoint tiles in case line is contained withing a single tile
tileHash[tilebelt.pointToTile(coordinates[i][0], coordinates[i][1], max_zoom).join('/')] = true;
tileHash[tilebelt.pointToTile(coordinates[iNext][0], coordinates[iNext][1], max_zoom).join('/')] = true;
// encode segments as tile fractions
var start = pointToTileFraction(coordinates[i][0], coordinates[i][1], max_zoom);
var stop = pointToTileFraction(coordinates[iNext][0], coordinates[iNext][1], max_zoom);
segments.push([[start[0], start[1]], [stop[0], stop[1]]]);
}

for (var i = 0; i < segments.length; i ++) {
// encode coordinates as tile relative pairs
segments[i][0] = pointToTileFraction(segments[i][0][0], segments[i][0][1], max_zoom);
segments[i][1] = pointToTileFraction(segments[i][1][0], segments[i][1][1], max_zoom);
// modified Bresenham digital differential analyzer algorithm
for (var i = 0; i < segments.length; i++) {
var x0 = segments[i][0][0];
y0 = segments[i][0][1];
x1 = segments[i][1][0];
Expand All @@ -307,23 +309,64 @@ function lineCover(coordinates, max_zoom) {
x1 = firstX;
y1 = firstY;
}
x0 = Math.floor(x0);
y0 = Math.floor(y0);
x1 = Math.floor(x1);
y1 = Math.floor(y1);
var dx = Math.abs(x1-x0);
var dy = Math.abs(y1-y0);
var sx = (x0 < x1) ? 1 : -1;
var sy = (y0 < y1) ? 1 : -1;
var err = dx - dy;

while(true) {
tileHash[x0+'/'+y0+'/'+max_zoom] = true;
if(x0 > x1) throw new Error('Unable to find end of segment');
if (x0==x1 && y0==y1) break;
var e2 = 2*err;
if (e2 >-dy){ err -= dy; x0 += sx; }
else if (e2 < dx){ err += dx; y0 += sy; }
var x0Floor = Math.floor(x0);
var y0Floor = Math.floor(y0);
var x1Floor = Math.floor(x1);
var y1Floor = Math.floor(y1);
/*
vertical intersects:
| | | |
| | | |
| | | |
*/
var x = 0;
while(x0+x <= x1Floor+1) {
var intersection = lineIntersects(Math.floor(x0+x), y0-10000, Math.floor(x0+x), y0+10000,
x0, y0, x1, y1);

// add tile to the left and right of the intersection
//todo: check intersect and the two tiles being hashed
if(intersection){
tileHash[Math.floor(intersection[0]-1)+'/'+Math.floor(intersection[1])+'/'+max_zoom] = true;
tileHash[Math.floor(intersection[0])+'/'+Math.floor(intersection[1])+'/'+max_zoom] = true;
}
x++;
}

/*
horizontal intersects
________
________
________
*/
// verify x0,y0 is top
if(y0 < y1) {
var firstX = x0;
var firstY = y0;
x0 = x1;
y0 = y1;
x1 = firstX;
y1 = firstY;
}
var x0Floor = Math.floor(x0);
var y0Floor = Math.floor(y0);
var x1Floor = Math.floor(x1);
var y1Floor = Math.floor(y1);
var y = 0;
while(y0+y >= y1Floor) {
var intersection = lineIntersects(x0-1000, Math.floor(y0+y), x0+1000, Math.floor(y0+y),
x0, y0, x1, y1);

// add tile above and below the intersection
if(intersection){
tileHash[Math.floor(intersection[0])+'/'+Math.floor(intersection[1])+'/'+max_zoom] = true;
tileHash[Math.floor(intersection[0])+'/'+Math.floor(intersection[1]-1)+'/'+max_zoom] = true;
}
y--;
}
}
return tileHash;
Expand All @@ -347,7 +390,7 @@ function pointToTileFraction (lon, lat, z) {
}

function hashMerge(hash1, hash2) {
var keys = Object.keys(hash2)
var keys = Object.keys(hash2);
for(var i = 0; i < keys.length; i++) {
hash1[keys[i]] = true;
}
Expand All @@ -356,7 +399,7 @@ function hashMerge(hash1, hash2) {

function hashToArray(hash) {
keys = Object.keys(hash);
var tiles = []
var tiles = [];
for(var i = 0; i < keys.length; i++) {
var tileStrings = keys[i].split('/');
tiles.push([parseInt(tileStrings[0]), parseInt(tileStrings[1]), parseInt(tileStrings[2])]);
Expand Down
2 changes: 1 addition & 1 deletion test/fixtures/building_out.geojson
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Original file line number Diff line number Diff line change
Expand Up @@ -162,4 +162,4 @@
}
}
]
}
}
31 changes: 31 additions & 0 deletions test/fixtures/donut_out.geojson
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Original file line number Diff line number Diff line change
Expand Up @@ -280,6 +280,37 @@
},
"properties": {}
},
{
"type": "Feature",
"geometry": {
"type": "Polygon",
"coordinates": [
[
[
-76.1517334,
45.46783598
],
[
-76.14624023,
45.46783598
],
[
-76.14624023,
45.47168826
],
[
-76.1517334,
45.47168826
],
[
-76.1517334,
45.46783598
]
]
]
},
"properties": {}
},
{
"type": "Feature",
"geometry": {
Expand Down
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