MKCoordinateRegionMakeWithDistance Problem

[HockeyHippo]

So basically I'm trying to make two zoom functions, zoom in and zoom out.

I looked at the documentation and this is what I found:

MKCoordinateRegionMakeWithDistance
Creates a new MKCoordinateRegion from the specified coordinate and distance values.

MKCoordinateRegion MKCoordinateRegionMakeWithDistance(
CLLocationCoordinate2D centerCoordinate,
CLLocationDistance latitudinalMeters,
CLLocationDistance longitudinalMeters
);
Parameters
centerCoordinate
The center point of the new coordinate region.
latitudinalMeters
The amount of north-to-south distance (measured in meters) to use for the span.
longitudinalMeters
The amount of east-to-west distance (measured in meters) to use for the span.
Return Value
A region with the specified values.

Availability
Available in iOS 3.0 and later.
Declared In
MKGeometry.h

So then I declared my two variables

	CLLocationDistance latitudinalMeters;
	latitudinalMeters = 200000;
	CLLocationDistance longitudinalMeters;
	longitudinalMeters = 200000;

And created these two functions:

-(IBAction) zoomOut: (MKMapView *) mapView: (CLLocationDistance *) latitudinalMeters: (CLLocationDistance *) longitudinalMeters{
	
	CLLocationCoordinate2D coordinate;
	coordinate.latitude =  mapView.userLocation.location.coordinate.latitude;
	coordinate.longitude = mapView.userLocation.location.coordinate.longitude;
	longitudinalMeters += 10000;
	latitudinalMeters += 10000;
	mapView.region = MKCoordinateRegionMakeWithDistance(coordinate, latitudinalMeters, longitudinalMeters);


}

-(IBAction) zoomIn: (MKMapView *) mapView: (CLLocationDistance *) latitudinalMeters: (CLLocationDistance *) longitudinalMeters{
	
	CLLocationCoordinate2D coordinate;
	coordinate.latitude =  mapView.userLocation.location.coordinate.latitude;
	coordinate.longitude = mapView.userLocation.location.coordinate.longitude;
	longitudinalMeters -= 10000;
	latitudinalMeters -=  10000;
	mapView.region = MKCoordinateRegionMakeWithDistance(coordinate, latitudinalMeters, longitudinalMeters);

}

But it keeps saying:

error: incompatible type for argument 2 of 'MKCoordinateRegionMakeWithDistance'

x4


Can I not use a variable here?

[Duncan C]

Originally Posted by HockeyHippo

So basically I'm trying to make two zoom functions, zoom in and zoom out.


<snip>
Can I not use a variable here?

Of course you can use a variable. The problem is that your methods are set up to take POINTERS to CLLocationDistance values as parameters. CLLocationDistance is a simple data type. You don't want the asterisks in the parameter types. Your method declarations should look like this:

-(IBAction) zoomOut: (MKMapView *) mapView: (CLLocationDistance) latitudinalMeters: (CLLocationDistance) longitudinalMeters
{
//code
}

-(IBAction) zoomIn: (MKMapView *) mapView: (CLLocationDistance) latitudinalMeters: (CLLocationDistance) longitudinalMeters
{
//code
}

Another problem with your code is that you are setting the initial span to 200 kilometers, which is pretty big, and then zooming in or out by 1 km for each click. Initially, that will make for a 0.5% change in zoom level. However, if you click "zoom out" enough times, the zoom level will go negative. Bad things will likely happen if you try to specify a negative zoom level.

If instead you zoom OUT over and over from 200 km, the 1KM you add each time will be a smaller and smaller change in total zoom level to the point where you won't even be able to see the change. Imagine a zoom change from 1000 km to 1001 km. Do you think you could even see it unless you were pixel peeking?

You should really be multiplying/dividing the previous latitudinalMeters/longitudinalMeters values by some constant like 1.1. Multiplying by 1.1 would make the map zoom out 10%, and dividing by 1.1. would make it zoom IN by 10%, no matter what the zoom level. That's what you want.

[HockeyHippo]

Thank you so much!

I know that the values I had were not very appropriate. To be honest those numbers are pretty random :P I just wanted to get it to build first before I spent the time to adjust the numbers to get them right.

Anyways, the pointer change made it work! Thanks so much!