# distance_calculator

The distance calculator is a module for calculating distance between two geographic locations. It measures the distance along the surface of the earth. Formula takes into consideration the radius of the earth. For this algorithm, it is necessary to define an object that has longitude and latitude properties like this:

(location:Location {lat: 44.1194, lng: 15.2314})
TraitValue
Module typemodule
ImplementationC++
Graph directionundirected
Edge weightsunweighted
Parallelismsequential

## Procedures

### single()

Measures a distance from the start node to the end node.

#### Input:

• subgraph: Graph (OPTIONAL) ➡ A specific subgraph, which is an object of type Graph returned by the project() function, on which the algorithm is run.
• start: Vertex ➡ Starting point to measure distance. Required to have lng and lat properties.
• end: Vertex ➡ Ending point to measure distance. Required to have lng and lat properties.
• metrics: string ➡ Can be either "m" or "km". These stand for meters and kilometers respectively.
• decimals:int ➡ Number of decimals to round up the result.

#### Output:

• distance: double ➡ The final result obtained by calculating distance (in 'm' or 'km') between the 2 points that each have its latitude and longitude properties.

#### Usage:

The following query measures a distance from the start node to the end node:

MATCH (n:Location), (m:Location)
CALL distance_calculator.single(m, n, 'km')
YIELD distance
RETURN distance;

### multiple()

The procedure calculates the distance from all nodes from a start list, to all the nodes from an end list.

#### Input:

• subgraph: Graph (OPTIONAL) ➡ A specific subgraph, which is an object of type Graph returned by the project() function, on which the algorithm is run.
• start_points: List[Vertex] ➡ Starting points to measure distance collected in a list. Required to have lng and lat properties. Must be of the same size as end_points.
• end_points: List[Vertex] ➡ Ending points to measure distance collected in a list. Required to have lng and lat properties. Must be of the same size as start_points.
• metrics: string ➡ Can be either "m" or "km". These stand for metres and kilometres respectively.
• decimals:int ➡ Number of decimals to round up the result.

#### Output:

• distance: List[double] ➡ The final result obtained by calculating distance (in 'm' or 'km') from all the nodes from the start list, to all the nodes from the end list.

#### Usage:

MATCH (n), (m)
WITH COLLECT(n) AS location_set1, COLLECT(m) AS location_set2
CALL distance_calculator.multiple(location_set1, location_set2, 'km') YIELD distances
RETURN distances;

## Examples

Calculate distance between Zagreb and Zadar.

### Database state

The database contains the following data:

Created with the following Cypher queries:

CREATE (location:Location {name: 'Zagreb', lat: 45.8150, lng: 15.9819});
CREATE (location:Location {name: 'Zadar', lat: 44.1194, lng: 15.2314});

### Calculate distance

MATCH (n {name: 'Zagreb'}), (m {name: 'Zadar'})
CALL distance_calculator.single(n, m, 'km') YIELD distance
RETURN distance;

Result:

+----------+
| distance |
+----------+
| 197.568  |
+----------+

Calculate distance between:

### Database state

The database contains the following data:

Created with the following Cypher queries:

CREATE (location:Location {name: 'Samobor', county: 'Zagrebacka', lat: 45.8011, lng: 15.7110});
CREATE (location:Location {name: 'Velika Gorica', county: 'Zagrebacka', lat: 45.7142, lng: 16.0752});

### Calculate distance

Get the values using the following query:

MATCH (n:Location {county: "Zagrebacka"})
WITH  COLLECT(n) as ZG, COLLECT(m) as ZD
CALL distance_calculator.multiple(ZG, ZD, "km", 2) YIELD distances
RETURN ZG, ZD, distances;

Results (the information about nodes in the lists have been shortened to include only city names):

+----------------+------------+-----------+
| ZG             | ZD         | distances |
+----------------+------------+-----------+
| Samobor        | Zadar      | 190.76    |
+----------------+------------+-----------+
| Velika Gorica  | Zadar      | 189.37    |
+----------------+------------+-----------+
| Samobor        | Biograd    | 208.31    |
+----------------+------------+-----------+
| Velika Gorica  | Biograd    | 203.76    |
+----------------+------------+-----------+