Ytukyg

Using OL4 and Angular 5, I want to calculate the shortest line between two geometries, because I want to draw the shortest line between two geometries.

for example I have two polygons like this:

const geom1 = new ol_geom_Polygon([[[39.08317178, 34.94428969], [40.15753633, 35.19891679], 

        [40.09419625, 35.46617166], [39.0198317, 35.21154456], [39.08317178, 34.94428969]]]);



const geom2 = new ol_geom_Polygon([[[42.06884752, 37.70855705], [41.28393081, 37.41465862], 

        [41.93091268, 36.88185002], [42.06884752, 37.70855705]]]);

OL4 geometry class has getClosestPoint function but it return the closest point of the geometry to a passed point.

I need a similar function but it receive a geometry object instead of point.

Regards.

I think any shortest line will always include one of the vertices of one of the linestrings (for polygons the linestrings will be the outer rings), therefore whichever of those coordinates gives the closest closest point is the shortest line. I've checked the source code for getClosestPoint and it uses a simple pythagoras distance calculation, so geometries should be transformed to map coordinates before calling a function such as this which returns a line from geom1 to geom2 where the geometries can be single polygons and/or single linestrings.

function getShortestLine(geom1, geom2) {



    var result;

    var distanceSq = Infinity;



    (geom1.getLinearRing ? geom1.getLinearRing(0) : geom1).getCoordinates().forEach(function(coordinates) {

        var closest = geom2.getClosestPoint(coordinates);

        var distanceNew = Math.pow(closest[0]-coordinates[0],2) + Math.pow(closest[1]-coordinates[1],2);

        if (distanceNew < distanceSq) {

            distanceSq = distanceNew;

            result = [ coordinates, closest ];

        }

    });



    (geom2.getLinearRing ? geom2.getLinearRing(0) : geom2).getCoordinates().forEach(function(coordinates) {

        var closest = geom1.getClosestPoint(coordinates);

        var distanceNew = Math.pow(closest[0]-coordinates[0],2) + Math.pow(closest[1]-coordinates[1],2);

        if (distanceNew < distanceSq) {

            distanceSq = distanceNew;

            result = [ closest, coordinates ];

        }

    });



    return new ol.geom.LineString(result);



}

Actually, Mike's answer is about 95% perfect :) .. so I done some improvements and here is the final code in TypeScript:

  public getShortestLine(geom1: ol_geom_Geometry, geom2: ol_geom_Geometry): ol_geom_LineString {

    if (geom1.getType() === 'Point' && geom2.getType() === 'Point') {

      return new ol_geom_LineString([(geom1 as ol_geom_Point).getCoordinates(), (geom2 as ol_geom_Point).getCoordinates()]);

    }



    let result = ;

    let distanceSq = Infinity;



    let geom1Coordinates = ;

    if (geom1.getType() === 'Polygon') {

      geom1Coordinates = (geom1 as ol_geom_Polygon).getLinearRing(0).getCoordinates();

    } else if (geom1.getType() === 'Point') {

      geom1Coordinates = [(geom1 as ol_geom_Point).getCoordinates()];

    } else {

      geom1Coordinates = (geom1 as any).getCoordinates();

    }



    let geom2Coordinates = ;

    if (geom2.getType() === 'Polygon') {

      geom2Coordinates = (geom2 as ol_geom_Polygon).getLinearRing(0).getCoordinates();

    } else if (geom2.getType() === 'Point') {

      geom2Coordinates = [(geom2 as ol_geom_Point).getCoordinates()];

    } else {

      geom2Coordinates = (geom2 as any).getCoordinates();

    }



    geom1Coordinates.forEach(coordinates => {

      const closest = geom2.getClosestPoint(coordinates);

      const distanceNew = Math.pow(closest[0] - coordinates[0], 2) + Math.pow(closest[1] - coordinates[1], 2);

      if (distanceNew < distanceSq) {

        distanceSq = distanceNew;

        result = [coordinates, closest];

      }

    });



    geom2Coordinates.forEach(coordinates => {

      const closest = geom1.getClosestPoint(coordinates);

      const distanceNew = Math.pow(closest[0] - coordinates[0], 2) + Math.pow(closest[1] - coordinates[1], 2);

      if (distanceNew < distanceSq) {

        distanceSq = distanceNew;

        result = [closest, coordinates];

      }

    });



    return new ol_geom_LineString(result);

  }