## Converting Java formula to work with Mendix

0
Hi!   I am creating a java action to calculate the distance between two points using the haversine formula. I already found the following code which I am sure works. public static double distance(double lat1, double lat2, double lon1, double lon2) { final int R = 6371; // Radius of the earth double latDistance = Math.toRadians(lat2 - lat1); double lonDistance = Math.toRadians(lon2 - lon1); double a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2) + Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) * Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2); double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)); double distance = R * c * 1000; // convert to meters double height = el1 - el2; distance = Math.pow(distance, 2); return Math.sqrt(distance); } But when I paste this into my java action inside of Eclipse, I get some syntax errors in the first 2 lines, telling me to the comma's have to be replaced by semicolons.   The lat1, lat2, etc. values have to be equal to the following: public class JA_Henry_CalculateDistance extends CustomJavaAction<java.math.BigDecimal> { private java.math.BigDecimal LatitudeStartingPoint; private java.math.BigDecimal LongitudeStartingPoint; private java.math.BigDecimal LatitudeDestination; private java.math.BigDecimal LongitudeDestination; public JA_Henry_CalculateDistance(IContext context, java.math.BigDecimal LatitudeStartingPoint, java.math.BigDecimal LongitudeStartingPoint, java.math.BigDecimal LatitudeDestination, java.math.BigDecimal LongitudeDestination) { super(context); this.LatitudeStartingPoint = LatitudeStartingPoint; this.LongitudeStartingPoint = LongitudeStartingPoint; this.LatitudeDestination = LatitudeDestination; this.LongitudeDestination = LongitudeDestination; }   I'm new to Java and Mendix and I'm not finding a lot on syntax online.  Any help would be appreciated!   Thanks in advance.
3

Hi Henry,

You'll need to do some conversions because decimals are put into the Java action as BigDecimals and the function provided uses doubles. Easiest method is to just create doubles from the input then create a new BigDecimal as output. I've found this works for me:

``````		double latStartDouble = LatStart.doubleValue();
double latEndDouble = LatEnd.doubleValue();
double longStartDouble = LongStart.doubleValue();
double longEndDouble = LongEnd.doubleValue();
final int R = 6371; // Radius of the earth

double latDistance = Math.toRadians(latEndDouble - latStartDouble);
double lonDistance = Math.toRadians(longStartDouble - longEndDouble);
double a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2) + Math.cos(Math.toRadians(latStartDouble))
* Math.cos(Math.toRadians(latEndDouble)) * Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2);
double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
double distance = R * c * 1000; // convert to meters

distance = Math.pow(distance, 2);

return new BigDecimal(Math.sqrt(distance));``````

Note that you'll need to remove the first line of the provided function, as it’s not necessary for the Java action.

0

Hi Henry,

You can refer to the code below:

``````public class JA_Henry_CalculateDistance extends CustomJavaAction<java.math.BigDecimal>
{
private java.math.BigDecimal lat1;
private java.math.BigDecimal lat2;
private java.math.BigDecimal lon1;
private java.math.BigDecimal lon2;

public JA_Henry_CalculateDistance(IContext context, java.math.BigDecimal lat1, java.math.BigDecimal lat2, java.math.BigDecimal lon1, java.math.BigDecimal lon2)
{
super(context);
this.lat1 = lat1;
this.lat2 = lat2;
this.lon1 = lon1;
this.lon2 = lon2;
}

@java.lang.Override
public java.math.BigDecimal executeAction() throws Exception
{
// BEGIN USER CODE

double lat1D=lat1.doubleValue();
double lat2D=lat2.doubleValue();
double lon1D=lon1.doubleValue();
double lon2D=lon2.doubleValue();

double dis = this.distance(lat1D, lat2D, lon1D, lon2D);

return new BigDecimal(dis);

// END USER CODE
}

/**
* Returns a string representation of this action
* @return a string representation of this action
*/
@java.lang.Override
public java.lang.String toString()
{
return "JA_Henry_CalculateDistance";
}

// BEGIN EXTRA CODE

public static double distance(double lat1, double lat2, double lon1,
double lon2) {

final int R = 6371; // Radius of the earth

double latDistance = Math.toRadians(lat2 - lat1);
double lonDistance = Math.toRadians(lon2 - lon1);
double a = Math.sin(latDistance / 2) * Math.sin(latDistance / 2)
* Math.sin(lonDistance / 2) * Math.sin(lonDistance / 2);
double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));

double distance = R * c * 1000; // convert to meters

distance = Math.pow(distance, 2);

return Math.sqrt(distance);
}

// END EXTRA CODE``````