Get the certain area in the map?

userwfvk1 0
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I am working on Xamarin Forms with Maps. I need to get a certain area within the map and check if the user are inside of this area. for example, There is a certain village that I want to get the whole area and coordinates? I only i tried pin location but there is only 2 coordinates and cannot really determine if the user is inside the area.

I am going to save the area in my database and I already figured how to do this. but I don't know how can I get the coordinates of the certain area. How can I achieve this in Xamarin Forms?

I added an image for example, How Can I the the boxed area?enter image description here

xamarin.forms
1 Answers

First of all, Thank you @Jason for the provided links of answers.

I came up with this solution referencing to this question.

Checking if a longitude/latitude coordinate resides inside a complex polygon in an embedded device?

As I have mention on the comments above, I have a set of coordinates(lat/lng) inside my database and draw it on my maps in android to form a rectangular shape using polyline.

To check if the user is inside the drawn rectangle. I have modified the answer of Drew Noakes in the provided link above of this answer.

CODE

        /// <summary>
        /// Check if the user's location is inside the rectangle
        /// </summary>
        /// <param name="location">Current user's location</param>
        /// <param name="_vertices">Rectangular shape for checking</param>
        /// <returns></returns>
        private bool CheckUserLocation(Location location, Polyline _vertices)
        {
            var lastPoint = _vertices.Geopath[_vertices.Geopath.Count - 1];
            var isInside = false;
            var x = location.Longitude;
            foreach (var point in _vertices.Geopath)
            {
                var x1 = lastPoint.Longitude;
                var x2 = point.Longitude;
                var dx = x2 - x1;

                if (Math.Abs(dx) > 180.0)
                {
                    
                    if (x > 0)
                    {
                        while (x1 < 0)
                            x1 += 360;
                        while (x2 < 0)
                            x2 += 360;
                    }
                    else
                    {
                        while (x1 > 0)
                            x1 -= 360;
                        while (x2 > 0)
                            x2 -= 360;
                    }
                    dx = x2 - x1;
                }

                if ((x1 <= x && x2 > x) || (x1 >= x && x2 < x))
                {
                    var grad = (point.Latitude - lastPoint.Latitude) / dx;
                    var intersectAtLat = lastPoint.Latitude + ((x - x1) * grad);

                    if (intersectAtLat > location.Latitude)
                        isInside = !isInside;
                }
                lastPoint = point;
            }

            return isInside;
        }

If you are curious on how I tested it, here is what I did.

First, I retrieved my current location and manually draw a rectangle circulating on my location.

Second, Draw a second rectangle not so far away from my current location but outside the first drawn rectangle.

Third, I passed the first Polyline drawn on the function

CheckUserLocation(myCurrentLocation, firstRectangle) //THIS RETURNS TRUE

Another test is I passed the second rectangle to the function

CheckUserLocation(myCurrentLocation, secondRectangle) //THIS RETURNS FALSE

I will test it again if there is something wrong with this answer. But I hope someone will find this answer helpful.

userwfvk10
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