CLLocation - getDistanceFrom

[Newbie09]

Is anybody using this Class?
Here is my problem
<CODE>
CLLocation *loc1 = [[CLLocation alloc] initWithLatitude:+29.640426 longitude:-090.599039]; //70301
CLLocation *loc2 = [[CLLocation alloc] initWithLatitude:+38.637002 longitude:-090.650024]; //63005

double distance = [loc1 getDistanceFrom: loc2] / 1000;

NSLog(@"Distance between CoreLoc 70301 & 63005 = %g", distance);
</CODE>

Distance = 999.756

This returns a different value than google maps.

from: Chesterfield, MO 63005 to: THIBODAUX,LA - Google Maps

All in Kms. Is there a way to increase the acccuracy?

Thanks

[kendolondon]

Google maps is giving you the actual road distance travelled between the two locations whereas CLLocation is giving you straight line distance between the two.

I don't think there's anyway of getting turn-by-turn directions (and hence road distance) between two points in CLLocation and that's not supported in V3 either.

[Newbie09]

Originally Posted by kendolondon

Google maps is giving you the actual road distance travelled between the two locations whereas CLLocation is giving you straight line distance between the two.

I don't think there's anyway of getting turn-by-turn directions (and hence road distance) between two points in CLLocation and that's not supported in V3 either.

Thanks kendolondon. Yelp Apps - Does it mean that the distance provided in Yelp's restaurant search is just a Straight distance? I just compared the distance between Yelp's distance and Goolge maps distance. They are way off. How does this sound? May sound stupid, but no other go. Can I increase the straight distance by 10% to derive the road distance?

[kendolondon]

I'm not familiar with Yelp's App but, at a guess, they're probably querying a database that's off the device and the results are being returned with the distance already calculated - that's how I'd do it anyway! They could be using any method to calculate the distance although I doubt that they're doing a full route plan for every hit as that's quite a lot of processing just to get an accurate distance!

Whether adding an arbitrary 10% is a suitable option really depends on your application. You'll probably tend to find that the error between straight line and road distance actually increases the closer together the two items are. For example, in my town which has a large number of one way & pedestrian streets, getting to a location that's only 1km away in a straight line could easily be 2-3km by road! As you get up to 'big' distances, however, the percentage error is likely to become smaller.

I suspect most applications display their search results based on straight line distance and then compute the actual route distance only on demand so users are going to be used to this behavior.

[Newbie09]

Originally Posted by kendolondon

I'm not familiar with Yelp's App but, at a guess, they're probably querying a database that's off the device and the results are being returned with the distance already calculated - that's how I'd do it anyway! They could be using any method to calculate the distance although I doubt that they're doing a full route plan for every hit as that's quite a lot of processing just to get an accurate distance!

Whether adding an arbitrary 10% is a suitable option really depends on your application. You'll probably tend to find that the error between straight line and road distance actually increases the closer together the two items are. For example, in my town which has a large number of one way & pedestrian streets, getting to a location that's only 1km away in a straight line could easily be 2-3km by road! As you get up to 'big' distances, however, the percentage error is likely to become smaller.

I suspect most applications display their search results based on straight line distance and then compute the actual route distance only on demand so users are going to be used to this behavior.

Hey kendolondon. Thank you veru much. I just checked few apps that shows distance and all are straight line distance. I think I am gonna go with this approach until Apple comes with a Maps API that will give the road distance. Thanks a lot