title: $:/plugins/tiddlywiki/geospatial/docs

! Filter Operators

!! `geopoint` operator

The `geopoint` operator converts separate latitude, longitude and (optionally) altitude numbers into a [[GeoJSON Point Feature]] that can be used with other geospatial primitives.

The coordinates are specified as two or three operands:

```
[geopoint<latitude>,<longitude>,<attitude>]
```

Any operands that cannot be interpreted as a valid number will be interpreted as the value zero.

For example:

```
<$text text={{{ [geopoint[51.751944],[-1.257778]] }}}/>
```

Returns:

```
{"type":"Feature","properties":{},"geometry":{"type":"Point","coordinates":[51.751944,-1.257778,0]}}
```

!! `geodistance` operator

The `geodistance` operator calculates the distance between two points in [[GeoJSON Point Feature]] format. The points are specified as two operands. An optional third operand specifies the units as `miles`, `kilometers`, `degrees` or `radians` (defaults to `miles`).

```
<$let
	oxford={{{ [geopoint[51.751944],[-1.257778]] }}}
	new-york={{{ [geopoint[40.730610],[-73.935242]] }}}
>
<$text text={{{ [geodistance<oxford>,<new-york>] }}}/>,
<$text text={{{ [geodistance<oxford>,<new-york>,[miles]] }}}/>,
</$let>
```

!! `geounion` operator

The `geounion` operator calculates the union between two or more [[GeoJSON Polygon Features|GeoJSON Polygon Feature]].

Each input list item is interpreted as a [[GeoJSON Polygon Feature Collection]] containing polygons.

```
[geounion[]]
```

!! `geointersect` operator

The `geointersect` operator calculates the intersection between two or more [[GeoJSON Polygon Features|GeoJSON Polygon Feature]].

Each input list item is interpreted as a [[GeoJSON Polygon Feature Collection]] containing polygons.

```
[geointersect[]]
```

!! `geodifference` operator

The `geodifference` operator calculates the difference between two or more [[GeoJSON Polygon Features|GeoJSON Polygon Feature]].

Each input list item is interpreted as a [[GeoJSON Polygon Feature Collection]] containing polygons.

```
[geodifference[]]
```

!! `geolookup` operator

The `geolookup` operator identifies the polygon(s) within a [[GeoJSON Polygon Feature]] that correspond to a particular point, and returns the JSON properties of that polygon.

Each input list item is interpreted as a [[GeoJSON Point Feature]] and the operand is interpreted as a [[GeoJSON Polygon Feature Collection]].

For example, here we lookup the point 100.5,0.5 in the [[GeoJSON Polygon Feature Collection]] stored in the tiddler `TestData` and then extracts the indexes `0` and `animal` from the resulting JSON:

```
<$text text={{{ [geopoint[100.5],[0.5]geolookup{TestData}jsonget[0],[animal]] }}}/>
```

!! `olc-decode` operator

The `olc-decode` operator converts an [[OpenLocationCode|https://github.com/google/open-location-code]] shortcut into the [[GeoJSON Point Feature]] at its centre or the [[GeoJSON Polygon Feature]] representing the bounds of the area identified by the input code.

```
[olc-decode:bounds[9C3WQP2R+QV]]
[olc-decode:point[9C3WQP2R+QVH]]
```

!! `olc-encode` operator

The `old-encode` operator converts separate latitude and longitude numbers into an [[OpenLocationCode|https://github.com/google/open-location-code]] shortcut code with a specified length (defaults to 11 characters).

```
[olc-encode[51.751944],[-1.257778]]
[olc-encode[51.751944],[-1.257778],[11]]
```