rotate polygon around point in leaflet map

Question

I have an issue, in my leaflet map I\'ve created a triangle from polygon:

var polygon = L.polygon([ 
    [parseFloat(decimal_lat),parseFloat(decimal_lon)], 
         


        

Answer 1

I adapted @dooderson and @MBo from this question answers, the final code is something like this, it works perfectly!

rotatePoints (center, points, yaw) {
  const res = []
  const centerPoint = map.latLngToLayerPoint(center)
  const angle = yaw * (Math.PI / 180)
  for (let i = 0; i < points.length; i++) {
    const p = map.latLngToLayerPoint(points[i])
    // translate to center
    const p2 = new Point(p.x - centerPoint.x, p.y - centerPoint.y)
    // rotate using matrix rotation
    const p3 = new Point(Math.cos(angle) * p2.x - Math.sin(angle) * p2.y, Math.sin(angle) * p2.x + Math.cos(angle) * p2.y)
    // translate back to center
    let p4 = new Point(p3.x + centerPoint.x, p3.y + centerPoint.y)
    // done with that point
    p4 = map.layerPointToLatLng(p4)
    res.push(p4)
}
return res
}

Answer 2

One way to do it is through matrix rotation. https://en.wikipedia.org/wiki/Rotation_matrix. You want to translate the point to the center then apply the rotation, then translate it back.

This is what the end of your code would look like.

  //changing polyline with slider but I want to change polygon there
  range_yaw.onchange = function() {
    var yawAngle = (parseFloat(range_yaw.value) / (819 / 360) + 90)
    // line
    var center = [decimal_lat, decimal_lon]
    var end = [decimal_lat + 2, decimal_lon + 2]
    var pointListRotated = rotatePoints(center, [center, end], yawAngle)
    polyline.setLatLngs(pointListRotated);
    // polygon
    var polygonPoints = [
      center,
      [center[0] + 1, center[1] - 1],
      [center[0] + 1, center[1] + 1]
    ]
    polygonRotated = rotatePoints(center, polygonPoints, yawAngle)
    polygon.setLatLngs(polygonRotated)
  };

  //
  // rotate a list of points in [lat, lng] format about the center.
  //
  function rotatePoints(center, points, yaw) {
    var res = []
    var angle = yaw * (Math.PI / 180)
    for(var i=0; i<points.length; i++) {
      var p = points[i]
      // translate to center
      var p2 = [ p[0]-center[0], p[1]-center[1] ]
      // rotate using matrix rotation
      var p3 = [ Math.cos(angle)*p2[0] - Math.sin(angle)*p2[1], Math.sin(angle)*p2[0] + Math.cos(angle)*p2[1]]
      // translate back to center
      var p4 = [ p3[0]+center[0], p3[1]+center[1]]
      // done with that point
      res.push(p4)
    }
    return res
  }

Here is a DEMO

Answer 3

You can approach it a couple ways. Here is one...

FIRST: calculate the bearing and distance to the two 'outer' points from the anchor point. Here are a couple helper functions: https://github.com/gregallensworth/Leaflet/blob/master/LatLng_Bearings.js

SECOND: adjust those bearings however you want...keep the original distances.

THIRD: Using the new bearings and the distances, calculate the new LatLngs using the accepted answer here: How to calculate the latlng of a point a certain distance away from another? (This uses google maps instead of leaflet, but its easy to port to leaflet)

Let me know if you have any problems implementing...