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HTML

              
                <!--

Dont't forget to include the required css and javascript:
<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.7.2/leaflet.css" />
<script src="http://cdn.leafletjs.com/leaflet-0.7.2/leaflet.js"></script>

-->
<div id="map"></div>
              
            
!

CSS

              
                body,
html {
  height: 100%;
}
  
#map {
  width: 100%;
  height: 100%;
}
              
            
!

JS

              
                // dependencies and utilities

function geoBoundingBox (gj) {
  var coords, bbox

  if (!gj.hasOwnProperty('type')) return

  coords = getCoordinatesDump(gj)
  bbox = [Number.POSITIVE_INFINITY, Number.POSITIVE_INFINITY,
          Number.NEGATIVE_INFINITY, Number.NEGATIVE_INFINITY]
  return coords.reduce(function(prev,coord) {
    return [
      Math.min(coord[0], prev[0]),
      Math.min(coord[1], prev[1]),
      Math.max(coord[0], prev[2]),
      Math.max(coord[1], prev[3])
    ]
  }, bbox)
};

function getCoordinatesDump (gj) {
  var coords
 
  if (gj.type == 'Point') {
    coords = [gj.coordinates]
  } else if (gj.type == 'LineString' || gj.type == 'MultiPoint') {
    coords = gj.coordinates
  } else if (gj.type == 'Polygon' || gj.type == 'MultiLineString') {
    coords = gj.coordinates.reduce(function(dump, part) {
      return dump.concat(part);
    }, [])
  } else if (gj.type == 'MultiPolygon') {
    coords = gj.coordinates.reduce(function(dump, poly) {
      return dump.concat(poly.reduce(function(points,part) {
        return points.concat(part)
      },[]))
    },[])
  } else if (gj.type == 'Feature') {
    coords =  getCoordinatesDump(gj.geometry)
  } else if (gj.type == 'GeometryCollection') {
    coords = gj.geometries.reduce(function(dump, g) {
      return dump.concat(getCoordinatesDump(g))
    },[])
  } else if (gj.type == 'FeatureCollection') {
    coords = gj.features.reduce(function(dump, f) {
      return dump.concat(getCoordinatesDump(f))
    },[])
  }
  return coords
}

function createPolygonFromBounds (latLngBounds) {
  var center = latLngBounds.getCenter()
  var latlngs = []

  latlngs.push(latLngBounds.getSouthWest());//bottom left
  latlngs.push({ lat: latLngBounds.getSouth(), lng: center.lng })//bottom center
  latlngs.push(latLngBounds.getSouthEast()) // bottom right
  latlngs.push({ lat: center.lat, lng: latLngBounds.getEast() })// center right
  latlngs.push(latLngBounds.getNorthEast());// top right
  latlngs.push({ lat: latLngBounds.getNorth(), lng: map.getCenter().lng }) // top center
  latlngs.push(latLngBounds.getNorthWest()) // top left
  latlngs.push({ lat: map.getCenter().lat, lng: latLngBounds.getWest() }) // center left

  return new L.polygon(latlngs)
}

// copied from @mapbox/tilebelt

var d2r = Math.PI / 180,
    r2d = 180 / Math.PI;

/**
 * Get the bbox of a tile
 *
 * @name tileToBBOX
 * @param {Array<number>} tile
 * @returns {Array<number>} bbox
 * @example
 * var bbox = tileToBBOX([5, 10, 10])
 * //=bbox
 */
function tileToBBOX(tile) {
    var e = tile2lon(tile[0] + 1, tile[2]);
    var w = tile2lon(tile[0], tile[2]);
    var s = tile2lat(tile[1] + 1, tile[2]);
    var n = tile2lat(tile[1], tile[2]);
    return [w, s, e, n];
}

/**
 * Get a geojson representation of a tile
 *
 * @name tileToGeoJSON
 * @param {Array<number>} tile
 * @returns {Feature<Polygon>}
 * @example
 * var poly = tileToGeoJSON([5, 10, 10])
 * //=poly
 */
function tileToGeoJSON(tile) {
    var bbox = tileToBBOX(tile);
    var poly = {
        type: 'Polygon',
        coordinates: [[
            [bbox[0], bbox[1]],
            [bbox[0], bbox[3]],
            [bbox[2], bbox[3]],
            [bbox[2], bbox[1]],
            [bbox[0], bbox[1]]
        ]]
    };
    return poly;
}

function tile2lon(x, z) {
    return x / Math.pow(2, z) * 360 - 180;
}

function tile2lat(y, z) {
    var n = Math.PI - 2 * Math.PI * y / Math.pow(2, z);
    return r2d * Math.atan(0.5 * (Math.exp(n) - Math.exp(-n)));
}

// TODO: update this to support multiPolygon as well
// TODO: return a list of points that intersect instead
function polyIntersectsWithMultiPoly (poly, multiPoly) {
  var intersects = false

  poly.coordinates.forEach(function (coord1) {
    coord1.forEach(function (coord2) {
      const polyPoint = turf.point(coord2)

      if (turf.inside(polyPoint, multiPoly) && !intersects) {
        intersects = true
      }
    })
  })

  return intersects
}

// ------------------------------- actual issue

var map = L.map('map', {
  center: [36.1714895, -120.201561],
  zoom: 15,
  maxZoom: 21,
})

console.log('map', map.options)


// Create a Tile Layer and add it to the map
// var tiles = new L.tileLayer('http://{s}.tile.stamen.com/watercolor/{z}/{x}/{y}.png').addTo(map)

var tiles = L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png').addTo(map)

var shape = {
  "type": "Feature",
  "geometry": {
    "type":"MultiPolygon",
    "coordinates":[
      [
        [
          [
            -120.210483180564,
            36.1733407559931
          ],
          [
            -120.208957248083,
            36.1736847467392
          ],
          [
            -120.207629508842,
            36.1739369696058
          ],
          [
            -120.206294631218,
            36.1742082281604
          ],
          [
            -120.204985927664,
            36.1744794867151
          ],
          [
            -120.203515420763,
            36.1747983344899
          ],
          [
            -120.202270962657,
            36.1750529368174
          ],
          [
            -120.200993192097,
            36.1752789856131
          ],
          [
            -120.200326943015,
            36.1754360300395
          ],
          [
            -120.19920383742,
            36.175657319913
          ],
          [
            -120.198002209612,
            36.1759047838576
          ],
          [
            -120.196786305038,
            36.1761546272631
          ],
          [
            -120.195625128068,
            36.1763806760586
          ],
          [
            -120.195101646646,
            36.1764187474349
          ],
          [
            -120.195032642277,
            36.1764139885128
          ],
          [
            -120.194998495206,
            36.1764258657549
          ],
          [
            -120.194942222759,
            36.1763878144417
          ],
          [
            -120.194449674331,
            36.1758857481695
          ],
          [
            -120.193545479148,
            36.1749767940652
          ],
          [
            -120.192724565102,
            36.1741035318761
          ],
          [
            -120.192734082946,
            36.1739464874497
          ],
          [
            -120.192661603695,
            36.1739393828761
          ],
          [
            -120.192647457341,
            36.1734810410078
          ],
          [
            -120.192648435218,
            36.1731153152421
          ],
          [
            -120.192654746354,
            36.173069109145
          ],
          [
            -120.192648176705,
            36.1720294621949
          ],
          [
            -120.19265080181,
            36.1704700949203
          ],
          [
            -120.192648176705,
            36.1685097727573
          ],
          [
            -120.192643663427,
            36.1666986492261
          ],
          [
            -120.192638904505,
            36.1666248859348
          ],
          [
            -120.193309912509,
            36.1666225064739
          ],
          [
            -120.197186054487,
            36.1666034707858
          ],
          [
            -120.199351364003,
            36.1666106091687
          ],
          [
            -120.20003188985,
            36.1665939529418
          ],
          [
            -120.200986053714,
            36.1665939529418
          ],
          [
            -120.201055087253,
            36.1665531949778
          ],
          [
            -120.201302522027,
            36.1665558815657
          ],
          [
            -120.201426254,
            36.16668437246
          ],
          [
            -120.201602334114,
            36.1667343411411
          ],
          [
            -120.201666579561,
            36.1668342785033
          ],
          [
            -120.201816485605,
            36.1668771088014
          ],
          [
            -120.201878351591,
            36.1668556936525
          ],
          [
            -120.202006842485,
            36.1668771088014
          ],
          [
            -120.202009267592,
            36.1665995234639
          ],
          [
            -120.202144851224,
            36.1666034707858
          ],
          [
            -120.203731951714,
            36.1666010913248
          ],
          [
            -120.205077087342,
            36.166589594439
          ],
          [
            -120.206254180381,
            36.1665939529418
          ],
          [
            -120.207510535792,
            36.1665891940198
          ],
          [
            -120.207610473154,
            36.1665987118637
          ],
          [
            -120.208845413416,
            36.1669318364046
          ],
          [
            -120.210092250983,
            36.1671840592712
          ],
          [
            -120.210301643552,
            36.1673125501656
          ],
          [
            -120.210299264091,
            36.1674386615989
          ],
          [
            -120.210422996063,
            36.1674505589039
          ],
          [
            -120.210472964744,
            36.1674457999819
          ],
          [
            -120.210469095648,
            36.1697633885423
          ],
          [
            -120.210356371155,
            36.1697848101506
          ],
          [
            -120.210301643552,
            36.1698038458387
          ],
          [
            -120.210294505169,
            36.1698323993706
          ],
          [
            -120.210349232772,
            36.1698657118247
          ],
          [
            -120.210468829499,
            36.1699228119854
          ],
          [
            -120.210483180564,
            36.1733407559931
          ]
        ]
      ]
    ]
  }
}

var zoom = 19

var boundCoords = geoBoundingBox(shape)
var boundLatLngs = new L.latLngBounds(L.GeoJSON.coordsToLatLngs([[boundCoords[0], boundCoords[1]], [boundCoords[2], boundCoords[3]]]))
var boundShape = createPolygonFromBounds(boundLatLngs).setStyle({ color: 'yellow' })

var boundNorthEastCorner = boundLatLngs.getNorthEast()
var boundSouthWestCorner = boundLatLngs.getSouthWest()

var boundNorthWestCorner = boundLatLngs.getNorthWest()
var boundSouthEastCorner = boundLatLngs.getSouthEast()

console.log('bound corners [ne, sw, nw, se]', boundNorthEastCorner, boundSouthWestCorner, boundNorthWestCorner, boundSouthEastCorner)

var boundPoints = L.bounds(
  map.project(boundNorthWestCorner, zoom),
  map.project(boundSouthEastCorner, zoom)
)

var boundNorthWestMarker = L.marker(boundNorthWestCorner, { title: 'NW' })
var boundSouthEastMarker = L.marker(boundSouthEastCorner, { title: 'SE' })

console.log('boundaries', boundCoords, boundLatLngs, boundPoints, boundShape)
console.log('--- north west', boundNorthWestCorner)
console.log('--- south east', boundSouthEastCorner)

// @see https://gist.github.com/mourner/8825883
var tileBounds = L.bounds(
  boundPoints.min.divideBy(tiles.getTileSize().x).floor(),
  boundPoints.max.divideBy(tiles.getTileSize().x).floor()
)

console.log('tile bounds', tileBounds)

// var tileBoundsShape = createPolygonFromBounds(tileBounds).setStyle({ color: 'brown' })

// ------------------------------- intersection detection

// 1. avoid conversion altogether (try to stay with LatLng)
//  - probably not possible since we need to iterate through the coordinates (what would the base unit be?)
// 2. potentially use TurfJS http://turfjs.org/docs#squareGrid
// 3. look into vector math and calculus approaches to providing the intersection between the bbox and shape integrals as a grid of tiles
// 4. checkout https://github.com/tilemapjp/mbtiles.js/tree/master
// 5. write a custom CRS
// 6. check if the x/y values (before being converted back into lat/lng)
// 7. convert GeoJSON shape into x/y values
///   - convert x/y's that are scaled to tile boundaries into meters instead of the x/y (divided by 256)
//      * the problem is (likely) that we are checking tile indices and not x/y scaled to meters
//       - interestingly, these coordinates end up providing the correct result when `L.TileLayer.prototype.getTileUrl` is called
//    - ensure i/j is in meters

var dump = []

// TODO: test iterating through the width of a tile (in x/y) instead of tile indices
for (var j = tileBounds.min.y; j <= tileBounds.max.y; j += 1) {
  dump.push(new Array(tileBounds.max.y - tileBounds.min.y))

  for (var i = tileBounds.min.x; i <= tileBounds.max.x; i += 1) {
    var tilePoint = new L.Point(i, j) // RESEARCH: the x/y scaled to tile could be throwing this off
    // var tileLatLng = map.layerPointToLatLng(tilePoint) // FIXME: this value is experiencing drift!
    // var tileShape = { type: 'Point', coordinates: [tileLatLng.lng, tileLatLng.lat] }
    // var tileIntersects = gju.pointInPolygon(tileShape, shape)
    var tileShape = tileToGeoJSON([tilePoint.x, tilePoint.y, zoom])
    var tileIntersects = polyIntersectsWithMultiPoly(tileShape, shape)
    // var tileIntersects = turf.intersect(shape, tileShape)
 
    // console.log('\n--- tile lat/lng', tileLatLng)
    console.log('\n--- tile point', tilePoint)
    console.log('--- tile x/y (orig)', i, j)
    console.log('--- tile unprojected', map.unproject(tilePoint, 19))
    console.log('--- tile shape', tileShape)
    console.log('--- field shape', shape)
    console.log('--- tile pixel origin', map.getPixelOrigin(), map.unproject(map.getPixelOrigin()))
    console.log('--- intersects?', tileIntersects)
    
    L.geoJSON(tileShape, { style: { color: 'pink' }}).addTo(map)
 
    if (tileIntersects) {
      L.geoJSON(tileShape, { style: { color: 'teal' } }).addTo(map)
      // L.marker(tileLatLng, { title: 'Tile', style: { color: 'red' } })
      
      dump[j - tileBounds.min.y][i - tileBounds.min.x] = { tilePoint: tilePoint }//, tileLatLng: tileLatLng }
    }

    // FIXME: `tileLatLng` is drifting, causing `tileIntersects` to always be false
  }
}

// ---------------------------------- visualize the shapes

console.log('tile size', tiles.getTileSize().x)
console.log('tile bounds', tileBounds)
console.log('dump', dump)

var meta = {
  field: {
    bounds: boundCoords,
    shape: shape
  },
  tiles: {
    bounds: tileBounds,
    dimensions: {
      x: tiles.getTileSize().x,
      y: tiles.getTileSize().y
    }
  },
  zoom: zoom,
  dump: dump
}

console.log('meta', JSON.stringify(meta))

// boundNorthWestMarker.addTo(map)
// boundSouthEastMarker.addTo(map)
boundShape.addTo(map)

L.geoJSON(shape).addTo(map)
              
            
!
999px

Console