Calculate the distance between two points in iphon

问题:

I am creating an application that requires the user to input two places (Postal codes). My application will calculate the driving-distance between these two points ad output the result. The user has the option of adding Way-Points. I think I would have to use the google maps API and get an xml file with the result and then parse the xml file. Can anyone help me because i not sure how to do this. Appreciate all help.

Example... Start: BR1 1LR

Waypoint: BR2 0LH

Waypoint: BR3 4AY

Destination: BR1 1LR

回答1:

Yes you can calculate the distance ,for that you need to have the latitude and longitude to get the distance.Objective C provides the method to calculate the distance between points here is the example......

float distance =[mUserCurrentLocation distanceFromLocation:location1]/1000;

This will provide you the distance in Kilometers.

回答2:

I know this is really late, but I'm posting my solution to this in case anybody needs it.

Firstly, i declared the URL (the one that calls google maps api)

#define DST_API @"http://maps.googleapis.com/maps/api/distancematrix/xml?origins=%@&destinations=%@&units=%@&sensor=false"

Next I created a string containing this URL:

NSString *URL = [NSString stringWithFormat:DST_API, source, destination, units];

Where source, destination are strings containing the start point and end point. units can be @"imperial" or @"metric". Now that i had the URL, i would get back an xml string. To parse this, i used TBXML. There is always a large debate about which XML Parser to use. I used TBXML as it was easy, and is the fastest.

TBXML *directionsParser = [[TBXML alloc] initWithURL:[NSURL URLWithString:URL]];

// Check if the Overall status is OK
TBXMLElement *root = directionsParser.rootXMLElement;
TBXMLElement *element = [TBXML childElementNamed:@"status" parentElement:root]; 
NSString *value = [TBXML textForElement:element];
if ([value caseInsensitiveCompare:@"OK"] != NSOrderedSame) {
    [directionsParser release];
    return result;
}

Once checking the root status is OK, then obtain the result for the XPath expression: //row/element/distance/value

element = [TBXML childElementNamed:@"row" parentElement:root];
element = [TBXML childElementNamed:@"element" parentElement:element];
element = [TBXML childElementNamed:@"status" parentElement:element];
value = [TBXML textForElement:element];

// Check if the Element status is OK
if ([value caseInsensitiveCompare:@"OK"] != NSOrderedSame) {
        [directionsParser release];
    return result;
}

element = element->parentElement;

element = [TBXML childElementNamed:@"distance" parentElement:element];

//Note if you want the result as text, replace 'value' with 'text'
element = [TBXML childElementNamed:@"value" parentElement:element];

NSString *result = [TBXML textForElement:element];

[directionsParser release];
//Do what ever you want with result

If anyone wants to have a URL to include way points, then here it is

#define DIR_API @"http://maps.googleapis.com/maps/api/directions/xml?origin=%@&destination=%@&waypoints=%@&units=%@&sensor=false"

But to use way points, things work a bit differently as Jano pointed out.

回答3:

If you want the road distance you need to ask Google and then parse the resulting XML, using a XML parser and the XPath expression //leg/step/distance/value, which will give you all the distance, that you will have to sum. See this about parsing xml and using XPath expressions.

回答4:

The distanceFromLocation: method will give you the absolute distance between any two CLLocation points, not a driving distance. For that, you must use the Google Maps API as you suspected.