Mongo - GeoSpacial

Lesson Objectives

1. Explain GeoSpacial
2. Explain GeoJSON
3. Explain containers
4. Explain How To Create an Index
5. Explain $near
6. Explain $geoWithin
7. Explain $geoIntersects

Explain GeoSpacial

Explain GeoJSON

1. { type: "<GeoJSON type>" , coordinates: <coordinates> }
2. Always list coordinates in longitude, latitude order.
3. point

• { type: "Point", coordinates: [ 40, 5 ] }

1. line

• { type: "LineString", coordinates: [ [ 40, 5 ], [ 41, 6 ] ] }

1. polygons

• array of coordinate arrays (rings)
• at least four points and have same start/end position
• one outer ring and 0+ inner rings
• cannot self intersect
• single ring
• { type: "Polygon", coordinates: [ [ [ 0 , 0 ] , [ 3 , 6 ] , [ 6 , 1 ] , [ 0 , 0 ] ] ] }
• multiple rings
• 1st ring is outer ring
• Any interior ring must be entirely contained by the outer ring
• Interior rings cannot intersect or overlap each other
• Interior rings cannot share an edge.
• http://docs.mongodb.org/manual/_images/index-2dsphere-polygon-with-ring.png

{
  type: "Polygon",
  coordinates: [
    [
      [0, 0],
      [3, 6],
      [6, 1],
      [0, 0],
    ],
    [
      [2, 2],
      [3, 3],
      [4, 2],
      [2, 2],
    ],
  ],
}; 

Explain containers

1. MultiPoint

{
  type: "MultiPoint",
  coordinates: [
    [-73.958, 40.8003],
    [-73.9498, 40.7968],
    [-73.9737, 40.7648],
    [-73.9814, 40.7681],
  ],
}

1. MultiLineString

{
  type: "MultiLineString",
  coordinates: [
    [
      [-73.96943, 40.78519],
      [-73.96082, 40.78095],
    ],
    [
      [-73.96415, 40.79229],
      [-73.95544, 40.78854],
    ],
    [
      [-73.97162, 40.78205],
      [-73.96374, 40.77715],
    ],
    [
      [-73.9788, 40.77247],
      [-73.97036, 40.76811],
    ],
  ],
}

1. MultiPolygon

{
  type: "MultiPolygon",
  coordinates: [
    [
      [
        [-73.958, 40.8003],
        [-73.9498, 40.7968],
        [-73.9737, 40.7648],
        [-73.9814, 40.7681],
        [-73.958, 40.8003],
      ],
    ],
    [
      [
        [-73.958, 40.8003],
        [-73.9498, 40.7968],
        [-73.9737, 40.7648],
        [-73.958, 40.8003],
      ],
    ],
  ],
}

1. GeometryCollection

{
  type: "GeometryCollection",
  geometries: [
    {
      type: "MultiPoint",
      coordinates: [
        [-73.958, 40.8003],
        [-73.9498, 40.7968],
        [-73.9737, 40.7648],
        [-73.9814, 40.7681],
      ],
    },
    {
      type: "MultiLineString",
      coordinates: [
        [
          [-73.96943, 40.78519],
          [-73.96082, 40.78095],
        ],
        [
          [-73.96415, 40.79229],
          [-73.95544, 40.78854],
        ],
        [
          [-73.97162, 40.78205],
          [-73.96374, 40.77715],
        ],
        [
          [-73.9788, 40.77247],
          [-73.97036, 40.76811],
        ],
      ],
    },
  ],
}

Explain How To Create an Index

1. db.collection.createIndex( { <location field> : "2dsphere" } )

Explain $near

db.test_data.insert({
  name: "north",
  position: { type: "Point", coordinates: [0, 1] },
});
db.test_data.insert({
  name: "east",
  position: { type: "Point", coordinates: [1, 0] },
});
db.test_data.insert({
  name: "south",
  position: { type: "Point", coordinates: [0, -1] },
});
db.test_data.insert({
  name: "west",
  position: { type: "Point", coordinates: [-1, 0] },
});
db.test_data.createIndex({ position: "2dsphere" });

db.test_data.find({
  position: {
    $near: {
      $geometry: {
        type: "Point",
        coordinates: [2, 0],
      },
      $minDistance: 0,
      $maxDistance: 200000,
    },
  },
});

Explain $geoWithin

db.test_data.find({
  position: {
    $geoWithin: {
      $geometry: {
        type: "Polygon",
        coordinates: [
          [
            [0.5, 0.5],
            [1.5, 0.5],
            [1.5, -0.5],
            [0.5, -0.5],
            [0.5, 0.5], // VERY IMPORTANT
          ],
        ],
      },
    },
  },
});

Explain $geoIntersects

db.test_data.insert({
  name: "line",
  position: {
    type: "LineString",
    coordinates: [
      [1, 0],
      [2, 0],
    ],
  },
});
WriteResult({ nInserted: 1 });

db.test_data.find({
  position: {
    $geoIntersects: {
      $geometry: {
        type: "Polygon",
        coordinates: [
          [
            [0.5, 0.5],
            [1.5, 0.5],
            [1.5, -0.5],
            [0.5, -0.5],
            [0.5, 0.5], // VERY IMPORTANT
          ],
        ],
      },
    },
  },
});