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Snap to crossing between lines in OpenLayers

How to snap lines to points automatically?how to snap two line vertex in two different layers used in QGISSnap (editing tools) in ArcGIS not working properlyHow to snap a road network to a hexagonal grid in QGIS?Snap lines to polygon verticies at interscetionQGIS snap questionOpenLayers 4 between geometrySnap lines based on hierarchyHow to snap to intersection of lines with Classic snapping?PostGIS snap line segment endpoint to closest other line segment

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

Is it possible to let the snap interaction snap to the crossing of two different lines (or polygons) in OpenLayers?

It can snap to vertices and lines between vertices, but I can't see a way to snap to the crossing of different geometries.

asked Apr 3 at 15:00

Hansson

134

What is the nature of these lines/polygons? Can they be considered/combined to one geometry collection?

– TomazicM
Apr 3 at 16:33

No they are different polygons/lines. They might be combined temporarily for the snap calculation.

– Hansson
2 days ago

Then solution from @Mike should be accepted. Just take code from line source2.clear(); onward.

– TomazicM
2 days ago

add a comment |

Is it possible to let the snap interaction snap to the crossing of two different lines (or polygons) in OpenLayers?

It can snap to vertices and lines between vertices, but I can't see a way to snap to the crossing of different geometries.

asked Apr 3 at 15:00

Hansson

134

What is the nature of these lines/polygons? Can they be considered/combined to one geometry collection?

– TomazicM
Apr 3 at 16:33

No they are different polygons/lines. They might be combined temporarily for the snap calculation.

– Hansson
2 days ago

Then solution from @Mike should be accepted. Just take code from line source2.clear(); onward.

– TomazicM
2 days ago

add a comment |

Is it possible to let the snap interaction snap to the crossing of two different lines (or polygons) in OpenLayers?

It can snap to vertices and lines between vertices, but I can't see a way to snap to the crossing of different geometries.

asked Apr 3 at 15:00

Hansson

134

Is it possible to let the snap interaction snap to the crossing of two different lines (or polygons) in OpenLayers?

It can snap to vertices and lines between vertices, but I can't see a way to snap to the crossing of different geometries.

openlayers snapping

asked Apr 3 at 15:00

Hansson

134

asked Apr 3 at 15:00

Hansson

134

asked Apr 3 at 15:00

Hansson

134

asked Apr 3 at 15:00

Hansson

134

asked Apr 3 at 15:00

Hansson

134

What is the nature of these lines/polygons? Can they be considered/combined to one geometry collection?

– TomazicM
Apr 3 at 16:33

No they are different polygons/lines. They might be combined temporarily for the snap calculation.

– Hansson
2 days ago

Then solution from @Mike should be accepted. Just take code from line source2.clear(); onward.

– TomazicM
2 days ago

add a comment |

What is the nature of these lines/polygons? Can they be considered/combined to one geometry collection?

– TomazicM
Apr 3 at 16:33

No they are different polygons/lines. They might be combined temporarily for the snap calculation.

– Hansson
2 days ago

Then solution from @Mike should be accepted. Just take code from line source2.clear(); onward.

– TomazicM
2 days ago

What is the nature of these lines/polygons? Can they be considered/combined to one geometry collection?

– TomazicM
Apr 3 at 16:33

No they are different polygons/lines. They might be combined temporarily for the snap calculation.

– Hansson
2 days ago

Then solution from @Mike should be accepted. Just take code from line source2.clear(); onward.

– TomazicM
2 days ago

add a comment |

1 Answer
1

active

oldest

votes

You can use turf.js to calculate the intersection points of linestrings and polygons, and use those, either in a second source or a feature collection, to control your snap interaction. Unfortunately turf.js works only on EPSG:4326 geometry and the point at which geometries intersect can different depending on how they are projected, so instead of reprojecting view coordinates to lon/lat I define a temporary projection where the view projection coordinates are scaled down small enough (to values < 1) to be treated as lon/lat by turf.js. Here's a working demo http://mikenunn.16mb.com/demo/linestring-intersects.html If you draw two or more intersecting linestrings (it won't catch self-intersecting lines) the intersection points will be highlighted (for non-demo use the second source does not need be shown on to the map) and the snap interaction snaps to them.

Here's the code used in the demo:

<!DOCTYPE html>
<html>
<head>
<title>OpenLayers LineString Intersection</title>
<link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<script src="https://npmcdn.com/@turf/turf@5.1.6/turf.min.js"></script>
</head>
<body>
<div id="map" class="map"></div>
<script>

 var raster = new ol.layer.Tile(
 source: new ol.source.OSM() 
 );

 var source = new ol.source.Vector();

 var style = new ol.style.Style(
 stroke: new ol.style.Stroke(
 color: 'black',
 width: 5
 )
 );

 var vector = new ol.layer.Vector(
 source: source,
 style: style
 );

 var source2 = new ol.source.Vector();

 var style2 = new ol.style.Style(
 image: new ol.style.Circle(
 fill: new ol.style.Fill(
 color: 'red'
 ),
 radius: 5
 )
 );

 var vector2 = new ol.layer.Vector(
 source: source2,
 style: style2
 );

 var map = new ol.Map(
 layers: [raster, vector, vector2],
 target: 'map',
 view: new ol.View(
 center: [-11000000, 4600000],
 zoom: 4
 )
 );

 var viewProjection = map.getView().getProjection();

 var smallProjection = new ol.proj.Projection(
 code: 'small',
 units: 'm'
 );
 ol.proj.addProjection(smallProjection);

 var scale = ol.extent.getWidth(viewProjection.getExtent());

 var smallTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 var normalTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 ol.proj.addCoordinateTransforms(viewProjection, smallProjection, smallTransform, normalTransform);

 var format = new ol.format.GeoJSON();
 source.on(['addfeature','changefeature','removefeature'], function() 
 source2.clear();
 var features = source.getFeatures();
 for (var i=0; i<features.length; i++) 
 var geom = features[i].getGeometry().getType();
 if (geom == 'LineString' 
 );

 var draw = new ol.interaction.Draw(
 source: source,
 type: 'LineString'
 );
 map.addInteraction(draw);

 var snap = new ol.interaction.Snap(
 source: source2,
 pixelTolerance: 20
 );
 map.addInteraction(snap);

</script>
</body>
</html>

answered Apr 4 at 14:18

Mike

2,470139

Thank you for you good answer, but I was hoping for a solution within OpenLayers. We use various projections and until now we have avoided turf because of its size. We might have an option to do the intersection crossing check on the backend that could provide a snap point vector layer.

– Hansson
2 days ago

add a comment |

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Here's the code used in the demo:

<!DOCTYPE html>
<html>
<head>
<title>OpenLayers LineString Intersection</title>
<link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<script src="https://npmcdn.com/@turf/turf@5.1.6/turf.min.js"></script>
</head>
<body>
<div id="map" class="map"></div>
<script>

 var raster = new ol.layer.Tile(
 source: new ol.source.OSM() 
 );

 var source = new ol.source.Vector();

 var style = new ol.style.Style(
 stroke: new ol.style.Stroke(
 color: 'black',
 width: 5
 )
 );

 var vector = new ol.layer.Vector(
 source: source,
 style: style
 );

 var source2 = new ol.source.Vector();

 var style2 = new ol.style.Style(
 image: new ol.style.Circle(
 fill: new ol.style.Fill(
 color: 'red'
 ),
 radius: 5
 )
 );

 var vector2 = new ol.layer.Vector(
 source: source2,
 style: style2
 );

 var map = new ol.Map(
 layers: [raster, vector, vector2],
 target: 'map',
 view: new ol.View(
 center: [-11000000, 4600000],
 zoom: 4
 )
 );

 var viewProjection = map.getView().getProjection();

 var smallProjection = new ol.proj.Projection(
 code: 'small',
 units: 'm'
 );
 ol.proj.addProjection(smallProjection);

 var scale = ol.extent.getWidth(viewProjection.getExtent());

 var smallTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 var normalTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 ol.proj.addCoordinateTransforms(viewProjection, smallProjection, smallTransform, normalTransform);

 var format = new ol.format.GeoJSON();
 source.on(['addfeature','changefeature','removefeature'], function() 
 source2.clear();
 var features = source.getFeatures();
 for (var i=0; i<features.length; i++) 
 var geom = features[i].getGeometry().getType();
 if (geom == 'LineString' 
 );

 var draw = new ol.interaction.Draw(
 source: source,
 type: 'LineString'
 );
 map.addInteraction(draw);

 var snap = new ol.interaction.Snap(
 source: source2,
 pixelTolerance: 20
 );
 map.addInteraction(snap);

</script>
</body>
</html>

answered Apr 4 at 14:18

Mike

2,470139

Thank you for you good answer, but I was hoping for a solution within OpenLayers. We use various projections and until now we have avoided turf because of its size. We might have an option to do the intersection crossing check on the backend that could provide a snap point vector layer.

– Hansson
2 days ago

add a comment |

Here's the code used in the demo:

<!DOCTYPE html>
<html>
<head>
<title>OpenLayers LineString Intersection</title>
<link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<script src="https://npmcdn.com/@turf/turf@5.1.6/turf.min.js"></script>
</head>
<body>
<div id="map" class="map"></div>
<script>

 var raster = new ol.layer.Tile(
 source: new ol.source.OSM() 
 );

 var source = new ol.source.Vector();

 var style = new ol.style.Style(
 stroke: new ol.style.Stroke(
 color: 'black',
 width: 5
 )
 );

 var vector = new ol.layer.Vector(
 source: source,
 style: style
 );

 var source2 = new ol.source.Vector();

 var style2 = new ol.style.Style(
 image: new ol.style.Circle(
 fill: new ol.style.Fill(
 color: 'red'
 ),
 radius: 5
 )
 );

 var vector2 = new ol.layer.Vector(
 source: source2,
 style: style2
 );

 var map = new ol.Map(
 layers: [raster, vector, vector2],
 target: 'map',
 view: new ol.View(
 center: [-11000000, 4600000],
 zoom: 4
 )
 );

 var viewProjection = map.getView().getProjection();

 var smallProjection = new ol.proj.Projection(
 code: 'small',
 units: 'm'
 );
 ol.proj.addProjection(smallProjection);

 var scale = ol.extent.getWidth(viewProjection.getExtent());

 var smallTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 var normalTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 ol.proj.addCoordinateTransforms(viewProjection, smallProjection, smallTransform, normalTransform);

 var format = new ol.format.GeoJSON();
 source.on(['addfeature','changefeature','removefeature'], function() 
 source2.clear();
 var features = source.getFeatures();
 for (var i=0; i<features.length; i++) 
 var geom = features[i].getGeometry().getType();
 if (geom == 'LineString' 
 );

 var draw = new ol.interaction.Draw(
 source: source,
 type: 'LineString'
 );
 map.addInteraction(draw);

 var snap = new ol.interaction.Snap(
 source: source2,
 pixelTolerance: 20
 );
 map.addInteraction(snap);

</script>
</body>
</html>

answered Apr 4 at 14:18

Mike

2,470139

Thank you for you good answer, but I was hoping for a solution within OpenLayers. We use various projections and until now we have avoided turf because of its size. We might have an option to do the intersection crossing check on the backend that could provide a snap point vector layer.

– Hansson
2 days ago

add a comment |

Here's the code used in the demo:

<!DOCTYPE html>
<html>
<head>
<title>OpenLayers LineString Intersection</title>
<link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<script src="https://npmcdn.com/@turf/turf@5.1.6/turf.min.js"></script>
</head>
<body>
<div id="map" class="map"></div>
<script>

 var raster = new ol.layer.Tile(
 source: new ol.source.OSM() 
 );

 var source = new ol.source.Vector();

 var style = new ol.style.Style(
 stroke: new ol.style.Stroke(
 color: 'black',
 width: 5
 )
 );

 var vector = new ol.layer.Vector(
 source: source,
 style: style
 );

 var source2 = new ol.source.Vector();

 var style2 = new ol.style.Style(
 image: new ol.style.Circle(
 fill: new ol.style.Fill(
 color: 'red'
 ),
 radius: 5
 )
 );

 var vector2 = new ol.layer.Vector(
 source: source2,
 style: style2
 );

 var map = new ol.Map(
 layers: [raster, vector, vector2],
 target: 'map',
 view: new ol.View(
 center: [-11000000, 4600000],
 zoom: 4
 )
 );

 var viewProjection = map.getView().getProjection();

 var smallProjection = new ol.proj.Projection(
 code: 'small',
 units: 'm'
 );
 ol.proj.addProjection(smallProjection);

 var scale = ol.extent.getWidth(viewProjection.getExtent());

 var smallTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 var normalTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 ol.proj.addCoordinateTransforms(viewProjection, smallProjection, smallTransform, normalTransform);

 var format = new ol.format.GeoJSON();
 source.on(['addfeature','changefeature','removefeature'], function() 
 source2.clear();
 var features = source.getFeatures();
 for (var i=0; i<features.length; i++) 
 var geom = features[i].getGeometry().getType();
 if (geom == 'LineString' 
 );

 var draw = new ol.interaction.Draw(
 source: source,
 type: 'LineString'
 );
 map.addInteraction(draw);

 var snap = new ol.interaction.Snap(
 source: source2,
 pixelTolerance: 20
 );
 map.addInteraction(snap);

</script>
</body>
</html>

answered Apr 4 at 14:18

Mike

2,470139

Here's the code used in the demo:

<!DOCTYPE html>
<html>
<head>
<title>OpenLayers LineString Intersection</title>
<link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
<!-- The line below is only needed for old environments like Internet Explorer and Android 4.x -->
<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"></script>
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<script src="https://npmcdn.com/@turf/turf@5.1.6/turf.min.js"></script>
</head>
<body>
<div id="map" class="map"></div>
<script>

 var raster = new ol.layer.Tile(
 source: new ol.source.OSM() 
 );

 var source = new ol.source.Vector();

 var style = new ol.style.Style(
 stroke: new ol.style.Stroke(
 color: 'black',
 width: 5
 )
 );

 var vector = new ol.layer.Vector(
 source: source,
 style: style
 );

 var source2 = new ol.source.Vector();

 var style2 = new ol.style.Style(
 image: new ol.style.Circle(
 fill: new ol.style.Fill(
 color: 'red'
 ),
 radius: 5
 )
 );

 var vector2 = new ol.layer.Vector(
 source: source2,
 style: style2
 );

 var map = new ol.Map(
 layers: [raster, vector, vector2],
 target: 'map',
 view: new ol.View(
 center: [-11000000, 4600000],
 zoom: 4
 )
 );

 var viewProjection = map.getView().getProjection();

 var smallProjection = new ol.proj.Projection(
 code: 'small',
 units: 'm'
 );
 ol.proj.addProjection(smallProjection);

 var scale = ol.extent.getWidth(viewProjection.getExtent());

 var smallTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 var normalTransform = function(coordinates, output, dimensions) 
 var dims = dimensions 

 ol.proj.addCoordinateTransforms(viewProjection, smallProjection, smallTransform, normalTransform);

 var format = new ol.format.GeoJSON();
 source.on(['addfeature','changefeature','removefeature'], function() 
 source2.clear();
 var features = source.getFeatures();
 for (var i=0; i<features.length; i++) 
 var geom = features[i].getGeometry().getType();
 if (geom == 'LineString' 
 );

 var draw = new ol.interaction.Draw(
 source: source,
 type: 'LineString'
 );
 map.addInteraction(draw);

 var snap = new ol.interaction.Snap(
 source: source2,
 pixelTolerance: 20
 );
 map.addInteraction(snap);

</script>
</body>
</html>

answered Apr 4 at 14:18

Mike

2,470139

answered Apr 4 at 14:18

Mike

2,470139

answered Apr 4 at 14:18

Mike

2,470139

answered Apr 4 at 14:18

Mike

2,470139

Thank you for you good answer, but I was hoping for a solution within OpenLayers. We use various projections and until now we have avoided turf because of its size. We might have an option to do the intersection crossing check on the backend that could provide a snap point vector layer.

– Hansson
2 days ago

add a comment |

Thank you for you good answer, but I was hoping for a solution within OpenLayers. We use various projections and until now we have avoided turf because of its size. We might have an option to do the intersection crossing check on the backend that could provide a snap point vector layer.

– Hansson
2 days ago

Thank you for you good answer, but I was hoping for a solution within OpenLayers. We use various projections and until now we have avoided turf because of its size. We might have an option to do the intersection crossing check on the backend that could provide a snap point vector layer.

– Hansson
2 days ago

add a comment |

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