Arcade: Snap point to polyline (mid-segment)

Bud

Could an Arcade function be added to do the following:

Snap a point to a polyline — but snap it mid-segment, not just to the closest vertex.

The function would return the snapped point — as well as return the ID of the polyline the point was snapped to.

Thanks.

JohannesLindner · ‎03-20-2022

Yes, a snap function would be great.

In the meantime, you can do it yourself (this is in multiple of my Calculation Attribute Rules):

function closest_feature(test_feature, compare_feature_set) {
  // returns the feature of compare_feature_set that is closest to test_feature
  var min_distance = 9999999
  var closest_feature = null
  for(var f in compare_feature_set) {
    var d = Distance(test_feature, f)
    if(d < min_distance) {
      min_distance = d
      closest_feature = f
    }
  }
  return closest_feature
}

function project_orthogonally(point_geometry, line_geometry) {
  // returns a projection of the point_geometry onto the line_geometry
  // only start and end point of the line_geometry are considered!
  // https://de.wikipedia.org/wiki/Orthogonalprojektion
  // https://en.wikibooks.org/wiki/Linear_Algebra/Orthogonal_Projection_Onto_a_Line
  var p = point_geometry
  var r0 = line_geometry.paths[0][0]
  var r1 = line_geometry.paths[0][-1]
  var ux = r1.x - r0.x
  var uy = r1.y - r0.y
  var lambda = ((p.x-r0.x)*ux + (p.y-r0.y)*uy) / (ux*ux + uy*uy)
  var new_p = Point({"x": r0.x + lambda * ux, "y": r0.y + lambda * uy, "spatialReference": p.spatialReference})
  // if new_p is on the line defined by r0 and r1 but not on the actual line_geometry, snap it to the closest end point
  if(Disjoint(new_p, line_geometry)) {
    new_p = IIF(Distance(r0, p) < Distance(r1, p), r0, r1)
  }
  return new_p
}

function snap_point_to_polyline(point_geometry, polyline_geometry) {
  // returns a point that is snapped to the polyline_geometry
  
  // create feature set of the polyline's segments
  var sr = point_geometry.spatialReference
  var vertices = polyline_geometry.paths[0]
  var fs_segments = {"fields": [], "spatialReference": sr, "geometryType": "esriGeometryPolyline", "features": []}
  for(var s=0; s<Count(vertices)-1; s++) {
    var p0 = vertices[s]
    var p1 = vertices[s+1]
    Push(fs_segments.features, {"geometry": {"paths": [[ [p0.x, p0.y], [p1.x, p1.y] ]], "spatialReference": sr}})
  }
  fs_segments = FeatureSet(Text(fs_segments))
  // project point_geometry onto the closest segment
  var closest_segment_geo = Geometry(closest_feature(point_geometry, fs_segments))
  return project_orthogonally(point_geometry, closest_segment_geo ) 
}


var fs_lines = FeatureSetByName($datastore, "Lines")
// optionally, buffer
fs_lines = Intersects(fs_lines, Buffer($feature, 100))

var closest_line_geometry = Geometry(closest_feature($feature, fs_lines))
return snap_point_to_polyline(Geometry($feature), closest_line_geometry)

Bud · ‎03-30-2022

Bud · ‎07-10-2023

Although, I don't think those functions help with "snapping mid-segment".

JohannesLindner · ‎07-11-2023

Ooh, I missed that update, thanks for the link!

It actually does solve your problem.

function closest_feature(test_feature, compare_feature_set) {
    // ...
}
function project_orthogonally(point_geometry, line_geometry) {
    // ...
}
function snap_point_to_polyline(point_geometry, polyline_geometry) {
    // ...
}


var line = Polyline({
  paths: [[  [0, 0],  [1, 1],  [1, 5], ]],
    spatialReference: {wkid: 3857}
})
var p = Point({x: 2, y: 2, spatialReference: {wkid: 3857}})

var sp1 = snap_point_to_polyline(p, line)
var sp2 = NearestCoordinate(line, p).coordinate

Console("With 3 custom functions: " + sp1)
Console("With NearestCoordinate: " + sp2)

With 3 custom functions: {"spatialReference":{"wkid":3857},"x":1,"y":2}
With NearestCoordinate: {"spatialReference":{"wkid":3857},"x":1,"y":2}