Calculate MKCoordinateRegion with a fixed diagonal distance - ios

I want to calculate a MKCoordinateRegion with a diagonal distance of 30km and the proportions of the region should be the same as the maps frame.
My approach looks like this:
let alpha = atan(mapView.frame.width / mapView.frame.height).radiansToDegrees
let beta = 90 - alpha
let spanDiagonal = 30_000.0
let spanWidth = spanDiagonal * Double(cos(beta.degreesToRadians))
let spanHeight = sqrt(spanDiagonal * spanDiagonal + spanWidth * spanWidth)
let region = MKCoordinateRegionMakeWithDistance(mapView.centerCoordinate, spanWidth, spanHeight)
let tlLat = region.center.latitude + (region.span.latitudeDelta / 2.0)
let tlLong = region.center.longitude - (region.span.longitudeDelta / 2.0)
let brLat = region.center.latitude - (region.span.latitudeDelta / 2.0)
let brLong = region.center.longitude + (region.span.longitudeDelta / 2.0)
let tl = CLLocationCoordinate2D(latitude: tlLat, longitude: tlLong)
let br = CLLocationCoordinate2D(latitude: brLat, longitude: brLong)
print(MKMetersBetweenMapPoints(MKMapPointForCoordinate(tl), MKMapPointForCoordinate(br)))
I calculated the angle of the frame and then a triangle with this angle and a base of 30000. This resulted in what I thought the right span height and width.
The problem that I have is that the diagonal of the region is about 10km larger. I think the cause for this is the conversion of meters to degrees that is somehow wrong.
Do you see a problem with my approach or do you know any better way to calculate a region with the same proportions of the frame, a diagonal of 30km and the same center as the map?

I ended up using this awesome library which implements the Euclid algorithm and allows you to expand a bounding box around a coordinate. Exactly what I was looking for!

Related

Programmatically move in the direction camera is facing

I'm trying to move a user position marker in the direction the camera is facing. Kind of like you would control a character in a game.
Since camera in MapKit is aligned north, I thought for moving forward I'd add some latitude degrees and then rotate the resulting point on camera angle.
I have some converters from meters to how many degrees is that:
class Converter {
fileprivate static let earthRadius = 6378000.0 // meter
class func latitudeDegrees(fromMeter meter: Double) -> Double {
return meter / earthRadius * (180 / Double.pi)
}
class func longitudeDegress(fromMeter meter: Double, latitude: Double) -> Double {
return meter / earthRadius * (180 / Double.pi) / cos(latitude * Double.pi / 180)
}
}
So for moving forward, my code looks like this:
let latitudeDelta = Converter.latitudeDegrees(fromMeter: speed)
let y = userLocation.latitude + latitudeDelta
let x = userLocation.longitude
let a = -self.mapView.camera.heading * Double.pi / 180
self.userLocation = CLLocationCoordinate2D(latitude: x*sin(a) + y*cos(a), longitude:x*cos(a) - y*sin(a))
I've tried different approaches, and none seem to work. Is there something fundamentally wrong? Could it be that I also need to consider Earth curvature in the calculations?
After some more struggling, I found out that this problem is called "Direct Geodesic Problem". Here I found all the formulas I needed, but in the end used a great C library.

convert Lat/Long to X,Y Coordinates in iOS [duplicate]

I am showing an image in an UIImageView and i'd like to convert coordinates to x/y values so i can show cities on this image.
This is what i tried based on my research:
CGFloat height = mapView.frame.size.height;
CGFloat width = mapView.frame.size.width;
int x = (int) ((width/360.0) * (180 + 8.242493)); // Mainz lon
int y = (int) ((height/180.0) * (90 - 49.993615)); // Mainz lat
NSLog(#"x: %i y: %i", x, y);
PinView *pinView = [[PinView alloc]initPinViewWithPoint:x andY:y];
[self.view addSubview:pinView];
which gives me 167 as x and y=104 but this example should have the values x=73 and y=294.
mapView is my UIImageView, just for clarification.
So my second try was to use the MKMapKit:
CLLocationCoordinate2D coord = CLLocationCoordinate2DMake(49.993615, 8.242493);
MKMapPoint point = MKMapPointForCoordinate(coord);
NSLog(#"x is %f and y is %f",point.x,point.y);
But this gives me some really strange values:
x = 140363776.241755 and y is 91045888.536491.
So do you have an idea what i have to do to get this working ?
Thanks so much!
To make this work you need to know 4 pieces of data:
Latitude and longitude of the top left corner of the image.
Latitude and longitude of the bottom right corner of the image.
Width and height of the image (in points).
Latitude and longitude of the data point.
With that info you can do the following:
// These should roughly box Germany - use the actual values appropriate to your image
double minLat = 54.8;
double minLong = 5.5;
double maxLat = 47.2;
double maxLong = 15.1;
// Map image size (in points)
CGSize mapSize = mapView.frame.size;
// Determine the map scale (points per degree)
double xScale = mapSize.width / (maxLong - minLong);
double yScale = mapSize.height / (maxLat - minLat);
// Latitude and longitude of city
double spotLat = 49.993615;
double spotLong = 8.242493;
// position of map image for point
CGFloat x = (spotLong - minLong) * xScale;
CGFloat y = (spotLat - minLat) * yScale;
If x or y are negative or greater than the image's size, then the point is off of the map.
This simple solution assumes the map image uses the basic cylindrical projection (Mercator) where all lines of latitude and longitude are straight lines.
Edit:
To convert an image point back to a coordinate, just reverse the calculation:
double pointLong = pointX / xScale + minLong;
double pointLat = pointY / yScale + minLat;
where pointX and pointY represent a point on the image in screen points. (0, 0) is the top left corner of the image.

Calculating bounding box given center lat /long and distance on iOS?

In my iOS app I have a lat and long that gives me my location. I want to be able to calculate the bounding box that satisfies a certain distance d from my location. How can I do this?
TRY 1:
So I tried the solution given by #Neeku. I can see how it's supposed to return the right information but unfortunately it's off. So I don't think I can use it.
The code I wrote is this and I pass in 1000 meters:
MKCoordinateRegion startRegion = MKCoordinateRegionMakeWithDistance(center, meters, meters);
CLLocationCoordinate2D northWestCorner, southEastCorner;
northWestCorner.latitude = startRegion.center.latitude + .5 * startRegion.span.latitudeDelta;
northWestCorner.longitude = startRegion.center.longitude - .5 * startRegion.span.longitudeDelta;
southEastCorner.latitude = startRegion.center.latitude - .5 * startRegion.span.latitudeDelta;
southEastCorner.longitude = startRegion.center.longitude - .5 * startRegion.span.longitudeDelta;
NSLog(#"CENTER <%#,%#>", #(center.latitude),#(center.longitude));
NSLog(#"NW <%#,%#>, SE <%#,%#>",#(northWestCorner.latitude),#(northWestCorner.longitude),#(southEastCorner.latitude),#(southEastCorner.longitude));
So then the result is:
CENTER <38.0826682,46.3028721>
NW <38.08717278501047,46.29717303828632>, SE <38.07816361498953,46.29717303828632>
I then put that in google maps and get this: (see screenshot)
So then to my understanding the 1000 meters should go from the center to the sides of the box. The map is measuring the corner which should be OVER 1000 meters and it's actually just over 800 meters. This is the problem I am trying to solve.
I tried this method before and the distances simply aren't accurate. So, this solution has not worked for me. If you have more suggestions or maybe want to point out what is done wrong here please let me know.
Thank you
Let's say that your desired distance is 111 meters. Then you use the following code:
// 111 kilometers / 1000 = 111 meters.
// 1 degree of latitude = ~111 kilometers.
// 1 / 1000 means an offset of coordinate by 111 meters.
float offset = 1.0 / 1000.0;
float latMax = location.latitude + offset;
float latMin = location.latitude - offset;
// With longitude, things are a bit more complex.
// 1 degree of longitude = 111km only at equator (gradually shrinks to zero at the poles)
// So need to take into account latitude too, using cos(lat).
float lngOffset = offset * cos(location.latitude * M_PI / 180.0);
float lngMax = location.longitude + lngOffset;
float lngMin = location.longitude - lngOffset;
latMax, latMin, lngMax, lngMin will give you your bounding box coordinates.
(You can change this code pretty easily if you need distance other than 111 meters. Just update offset variable accordingly).
You can add/subtract half of the span from the latitude and longitude respectively and you get the values that you need:
CLLocationCoordinate2D centerCoord = CLLocationCoordinate2DMake(38.0826682, 46.3028721);
MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(centerCoord, 1000, 1000);
double latMin = region.center.latitude - .5 * startRegion.span.latitudeDelta;
double latMax = region.center.latitude + .5 * startRegion.span.latitudeDelta;
double lonMin = region.center.longitude - .5 * startRegion.span.longitudeDelta;
double lonMax = region.center.longitude + .5 * startRegion.span.longitudeDelta;
Just remember that:
latitudeDelta
The amount of north-to-south distance (measured in degrees) to display on the map. Unlike longitudinal distances, which vary based on
the latitude, one degree of latitude is always approximately 111
kilometers (69 miles).
longitudeDelta
The amount of east-to-west distance (measured in degrees) to display for the map region. The number of kilometers spanned by a
longitude range varies based on the current latitude. For example, one
degree of longitude spans a distance of approximately 111 kilometers
(69 miles) at the equator but shrinks to 0 kilometers at the poles.

convertCoordinate toPointToView returning bad results with tilted maps

I have a UIView overlayed on a map, and I'm drawing some graphics in screen space between two of the coordinates using
- (CGPoint)convertCoordinate:(CLLocationCoordinate2D)coordinate toPointToView:(UIView *)view
The problem is that when the map is very zoomed in and tilted (3D-like), the pixel position of the coordinate that is way off-screen stops being consistent. Sometimes the function returns NaN, sometimes it returns the right number and others it jumps to the other side of the screen.
Not sure how can I explain it better. Has anyone run into this?
During research have find a many solution. Any solution might be work for you.
Solution:1
int x = (int) ((MAP_WIDTH/360.0) * (180 + lon));
int y = (int) ((MAP_HEIGHT/180.0) * (90 - lat));
Solution:2
func addLocation(coordinate: CLLocationCoordinate2D)
{
// max MKMapPoint values
let maxY = Double(267995781)
let maxX = Double(268435456)
let mapPoint = MKMapPointForCoordinate(coordinate)
let normalizatePointX = CGFloat(mapPoint.x / maxX)
let normalizatePointY = CGFloat(mapPoint.y / maxY)
print(normalizatePointX)
print(normalizatePointX)
}
Solutuin:3
x = (total width of image in px) * (180 + latitude) / 360
y = (total height of image in px) * (90 - longitude) / 180
note: when using negative longitude of latitude make sure to add or subtract the negative number i.e. +(-92) or -(-35) which would actually be -92 and +35

Finding Bounding Box from CLLocationCoordinate2D

I am working with an API that allows me to specify a "bounding box" of coordinate which allows me to only return results within that box:
Returns a list of geocaches inside the specified bounding box sorted
by the distance from the center of the box.
The parameters south
latitude, west longitude, north latitude, east longitude define the
edges of a bounding box.
Coordinates should be in decimal degrees Use
positive numbers for north latitude and east longitude and negative
numbers of south latitude and west longitude.
The box cannot cross
the 180° longitude line or the 90° or -90° points.
The math for this is a little beyond me, but I found somewhat helpful calculations, but I am not sure it is what I need for the API:
MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(self.mapView.centerCoordinate, 2000.0, 2000.0);
CLLocationCoordinate2D northWestCorner, southEastCorner;
northWestCorner.latitude = center.latitude - (region.span.latitudeDelta / 2.0);
northWestCorner.longitude = center.longitude + (region.span.longitudeDelta / 2.0);
southEastCorner.latitude = center.latitude + (region.span.latitudeDelta / 2.0);
southEastCorner.longitude = center.longitude - (region.span.longitudeDelta / 2.0);
Does anyone know how I could do this? Are the calculations here not helpful in order to get the west longitude, north latitude, east longitude that define the edges of the bounding box?
EDIT:
The error I am getting:
Invalid value for parameter: bbox=south,west,north,east
Using the center value:
center=37.552821,-122.377413
Converted Box (after calculations from above):
bbox=37.561831,-122.388730,37.543811,-122.366096
Final Working code:
// Current distance
MKMapRect mRect = mapView.visibleMapRect;
MKMapPoint eastMapPoint = MKMapPointMake(MKMapRectGetMinX(mRect), MKMapRectGetMidY(mRect));
MKMapPoint westMapPoint = MKMapPointMake(MKMapRectGetMaxX(mRect), MKMapRectGetMidY(mRect));
CLLocationDistance distance = MKMetersBetweenMapPoints(eastMapPoint, westMapPoint);
// Region
MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(request.center, distance, distance);
CLLocationCoordinate2D northWestCorner, southEastCorner;
northWestCorner.latitude = request.center.latitude + (region.span.latitudeDelta / 2.0);
northWestCorner.longitude = request.center.longitude - (region.span.longitudeDelta / 2.0);
southEastCorner.latitude = request.center.latitude - (region.span.latitudeDelta / 2.0);
southEastCorner.longitude = request.center.longitude + (region.span.longitudeDelta / 2.0);
base = [base stringByAppendingFormat:#"bbox=%f,%f,%f,%f&", southEastCorner.latitude,northWestCorner.longitude,northWestCorner.latitude,southEastCorner.longitude];
You seem to have gotten your hemispheres reversed. North and east are positive. So if you start from the center latitude and you want to find the northern boundary you ADD half the delta, not subtract.

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