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MD2000 · #1 (**permalink**) 04-24-2005

Hello,
I have the latitude and longitude of a position. I need to get the nearest street for that point. Is this called reverse geocoding?
Does anyone have an C# example how to do that? I only found VisualBasic examples.
Which algorithm gives me the best result?

Bye,

MD

**Wilfried** · #2 (**permalink**) 04-26-2005

Hi,

This gets you the streetaddress where you are on. But oif course not the nearest one if you are not on a street. If you need that you have to make a circle, take a radius of lets say 5 meter, then calc position every 5 meter on the circumfence of the circle. If not found then increase radius with 5 meter and do the same on the new circumfence. Of course you have to stop on a given maxium. Be aware that involved people must know you make an assumption with this !

Code:

            Map map = MP.ActiveMap;
            Location Loc = map.GetLocation(Lat, Lon, 1);
            FindResults StreetResults = map.ObjectsFromPoint(map.LocationToX(Loc), map.LocationToY(Loc));

            foreach (object o in StreetResults) {
                Location StreetLoc = o as Location;
                if(StreetLoc != null && StreetLoc.StreetAddress != null) {
                    Console.WriteLine("value    " + StreetLoc.StreetAddress.Value);
                    Console.WriteLine("street   " + StreetLoc.StreetAddress.Street);
                    Console.WriteLine("postcode " + StreetLoc.StreetAddress.PostalCode);
                    Console.WriteLine("city     " + StreetLoc.StreetAddress.City);
                }
            }

MD2000 · #3 (**permalink**) 04-26-2005

Hello,
thanks for your reply. There are two things, which I dont understand.

I use the point (Lat: 48,37017; Long: 10,8903).

1. Why does the ObjectsFromPoint function has as a result serveral locations?
Some of the result locations have a StreetAddress. None of them have a city.
The street are "A7", "A95", but the shouldnt be next to the given location.

2. How can I make a circle around a position to find the nearest street?

Do I have to use the goto function to get proper results?

Bye,

MD

MD2000 · #4 (**permalink**) 04-26-2005

Hello,
i found out that you need to use the goto() method, so that it will work.

I still have no idea how to make a circle to get the nearest street. Could you help me?

Bye,

MD

MD2000 · #5 (**permalink**) 04-27-2005

Hello,
I tried to use the code of one of the articles about Reverse Geocoding in Delphi and tried to convert it to C#:

Code:

				// First, try to find real latitude/longitude
				Location Loc = map.GetLocation(latitude, longitude, 1);
				Loc.GoTo();
				FindResults StreetResults = map.ObjectsFromPoint(map.LocationToX(Loc), map.LocationToY(Loc));

				Boolean foundStreet = false;
				foreach (object o in StreetResults) 
				{
					if (o is Location) 
					{
						Location StreetLoc = o as Location;
						if(StreetLoc != null && StreetLoc.StreetAddress != null) 
						{
							text += "\"" + dateTime + "\",\"" + StreetLoc.StreetAddress.PostalCode + "\",\"" + StreetLoc.StreetAddress.City + "\",\"" + StreetLoc.StreetAddress.Street + "\",\"" + latitude + "\",\"" + longitude + "\"\r\n";
							foundStreet = true;
							break;
						}
					}
				}

				// no street found ==> search around in circles
				if (!foundStreet) 
				{
					double maxDistance = 0.4;
					double distance = 0.05;
					while (distance <= maxDistance) 
					{
						double radius = 1 / 60 / 1852 * distance;
						double circum = Math.Floor(distance * 2 * Math.PI);
						double count =  circum / 5;
						double angleInc = 360 / count;
						if (angleInc <= 0) 
						{
							foundStreet = false;
							break;
						}
						double angle = 0;

						while (angle < 360) 
						{
							double lat = calcLat(latitude, longitude, angle, radius);
							double lon = calcLon(latitude, longitude, angle, radius);

							Loc = map.GetLocation(lat, lon, 1);
							Loc.GoTo();
							StreetResults = map.ObjectsFromPoint(map.LocationToX(Loc), map.LocationToY(Loc));

							// Search with new coordinates
							foreach (object o in StreetResults) 
							{
								if (o is Location) 
								{
									Location StreetLoc = o as Location;
									if(StreetLoc != null && StreetLoc.StreetAddress != null) 
									{
										text += "\"" + dateTime + "\",\"" + StreetLoc.StreetAddress.PostalCode + "\",\"" + StreetLoc.StreetAddress.City + "\",\"" + StreetLoc.StreetAddress.Street + "\",\"" + latitude + "\",\"" + longitude + "\"\r\n";
										foundStreet = true;
										break;
									}
								}
							}		
							
							if (foundStreet)
								break;
							angle = angle + angleInc;
						}
						if (foundStreet) 
						{
							break;
						}
						distance = distance + 0.05;
					}
				}

				if (!foundStreet) 
				{
					text += "\"" + dateTime + "\",\"---\",\"---\",\"---\",\"" + latitude + "\",\"" + longitude + "\"\r\n";
				}
			}












		private static double calcLon (double latitude, double longitude, double angle, double radius) 
		{
			double r = angle * Math.PI / 180;
			double c = radius;
			double b = c * Math.Cos(r) / Math.Cos((latitude * Math.PI / 180));
			return longitude + b;

		}

		private static double calcLat (double latitude, double longitude, double angle, double radius) 
		{
			double r = angle * Math.PI / 180;
			double c = radius;
			double a = c * Math.Sin(r);
			return latitude + a;
		}

Something must be wrong. Could anyone please help me, because I dont't get any street names, when the position is only close to a street.

Bye,

MD

**Wilfried** · #6 (**permalink**) 04-27-2005

Hi,

I made the class in C3 for you. this is the code:

Code:

    public class MPPosInCircle
    {
        int FMeterRes;      // position check resolution in meter
        int FMaxMeter;      // maximum size in meter of the circle radius

        public MPPosInCircle(int Resolution_meter, int MaxRadius_meter)
        {
            FMeterRes = Resolution_meter;
            FMaxMeter = MaxRadius_meter;
        }

        public delegate void Position(object sender, PositionArgs e);
        public event Position OnPosition;
        public class PositionArgs: EventArgs
        {
            double FLat;
            double FLon;
            int FRadius;
            Boolean FFound;

            public PositionArgs(double Lat, double Lon, int Radius)
            {
                FLat = Lat;
                FLon = Lon;
                FRadius = Radius;
            }

            public double Lat
            {
                get { return FLat; }
            }

            public double Lon
            {
                get { return FLon; }
            }

            public int Meter
            {
                get { return FRadius; }
            }

            public Boolean Found
            {
                get { return FFound; }
                set { FFound = value; }
            }
        }

        private double Deg2Rad(double degree)
        {
            return degree * Math.PI / 180;
        }

        /*private double Rad2Deg(double rad)
        {
            return rad * 180 / Math.PI;
        }*/

        private void CalcXY(double CenterLat, double CenterLon, double Angle, double Radius, out double Lat, out double Lon)
        {
            /*             B
                          /|
                         / |
                        /  |
                       /   |
                      /    |
                   c /     | a
                    /      |
                   /       |
                  /        |
                 /_________|
                A     b     C

                given A en c
                a = c * sin(A)
                b = c * cos(A)

                A == 0 is direction East in this drawing
                a = Latitude offset
                b = Longitude offset
                c = Radius of circle   */

            double r = Deg2Rad(Angle);
            double c = Radius;
            double a = c * Math.Sin(r);
            double b = c * Math.Cos(r) / Math.Cos(Deg2Rad(CenterLat));  // correct longitude for circle

            Lat = CenterLat + a;
            Lon = CenterLon + b;
        }

        public Boolean Execute(double CenterLat, double CenterLon)
        {
            double Lat, Lon;            // coordinate points on the circumfence of the circle
            double Radius;              // radius of the circle in degree
            Int32  Circum;              // circumfence of the circle in meter
            Int32  Count;               // the amount of points to calculate on the circumfence
            Int32  Angle;               // current angle against East to calculate in degree
            Int32  AngleInc;            // angle increments in degree per calculation
            Int32  Hits  = 0;           // count of hits calculated on the circumfence
            Int32  Meter = FMeterRes;   // Radius in meter, 1852 meter is 1 sea mile

            while (Meter <= FMaxMeter) {
                Radius   = (double)1 / 60 / 1852 * Meter;
                Circum   = (Int32)(Meter * 2 * Math.PI);
                Count    = Circum / FMeterRes;
                AngleInc = 360 / Count;

                if (AngleInc <= 0)
                    return false;
                Angle = 0;
                while (Angle < 360) {
                    CalcXY(CenterLat, CenterLon, Angle, Radius, out Lat, out Lon);
                    PositionArgs e = new PositionArgs(Lat, Lon, Meter);
                    if(OnPosition != null)
                        OnPosition(this, e);
                    if(e.Found)
                        Hits++;
                    Angle += AngleInc;
                }
                if (Hits > 0)
                    return true;
                Meter += FMeterRes;
            }
            return false;
        }
    }

To use it you can do something like this:

Code:

        public void PosInCirclePosition(object sender, MPPosInCircle.PositionArgs e)
        {
            double Alt = 1;
            Location Loc;
            //Location Loc;
            FindResults StreetResults;
            Pushpin PP;

            Loc = MP.ActiveMap.GetLocation(e.Lat, e.Lon, Alt);
            PP = MP.ActiveMap.AddPushpin(Loc, "");
            PP.Symbol = 2;
            StreetResults = MP.ActiveMap.ObjectsFromPoint(MP.ActiveMap.LocationToX(Loc), MP.ActiveMap.LocationToY(Loc));

            foreach(object o in StreetResults) {
                Location StreetLoc = o as Location;

                if(StreetLoc != null && StreetLoc.StreetAddress != null) {
                    Console.WriteLine("Found    " + StreetLoc.StreetAddress.Value);
                    //Console.WriteLine("postcode " + StreetLoc.StreetAddress.PostalCode);
                    Console.WriteLine("Distance " + Convert.ToString(e.Meter) + " meter from point");
                    e.Found = true;
                }
            }
        }

MD2000 · #7 (**permalink**) 04-27-2005

Hi Wilfried,
Thank you very much!
This will help me a lot, because I didn't understand the math part completely. I'll try the code soon.

Bye,

MD

MD2000 · #8 (**permalink**) 04-28-2005

Hello,
I'm not quite sure, how to use your methods. That's what I tried:

Code:

				MPPosInCircle.PositionArgs e = new MPPosInCircle.PositionArgs(latitude, longitude, 100);
				double Alt = 1;
				Location Loc;
				//Location Loc;
				FindResults StreetResults;
				Pushpin PP;

				Loc = map.GetLocation(e.Lat, e.Lon, Alt);
				PP = map.AddPushpin(Loc, "");
				PP.Symbol = 2;
				StreetResults = map.ObjectsFromPoint(map.LocationToX(Loc), map.LocationToY(Loc));

				foreach(object o in StreetResults) 
				{
					Location StreetLoc = o as Location;

					if(StreetLoc != null && StreetLoc.StreetAddress != null) 
					{
						Console.WriteLine("Found    " + StreetLoc.StreetAddress.Value);
						//Console.WriteLine("postcode " + StreetLoc.StreetAddress.PostalCode);
						Console.WriteLine("Distance " + Convert.ToString(e.Meter) + " meter from point");
						e.Found = true;
					}
				}

I don't know how to create the sender object.

Bye,

MD

**Wilfried** · #9 (**permalink**) 04-29-2005

Hi,

Quote:

I don't know how to create the sender object.

The code I posted was a quick copy/paste from some code of mine, so it is possible I forgot something

However what I did was following:

- find the address
- if not found create a class to search in circles

the class that runs in circles has an event handler and that's where the sender argument comes from.

I'm planning for a while to make an article for this but I dont got on time schedule

so please study the code snippets again and of cource dont hesitate to fire question on things that are not clear !

MD2000 · #10 (**permalink**) 04-30-2005

Hello,
I don't understand when and from where the Execute method is being called.

Bye,

Markus

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Getting street from latitude/longitude?

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