Drawing lat/lng points on an image

Question

I have the following:

• An image - a hand drawn map - of an area of roughly 600x400 meters. The image is drawn on top of Google Maps tiles.
• The latitude/longitude (from Google Maps) of the corners of this image. Or put differently, I have the north and south latitude and the east and west longitude of the image.
• A latitude/longitude coordinate from iPhone's CoreLocation.

How do I draw a point on this image (or nothing if it's out of bounds), representing the coordinate from CoreLocation?

Added bonus: draw an arrow on the edge of the map, pointing to the coordinate, if the coordinate is out of bounds of the image.

I would like to do this without using a library like proj, in order to not have to bundle a large library, and understand what I'm doing and why.

As you probably guessed by know, I'm writing this in Objective-C. Your answer doesn't have to be in Objective-C, though.

Answer 1

If I understand it correctly, you need to do two things. The first is to put your custom image into a map view and have your custom tiles appear at the correct coordinates, then pan, zoom and so on. The second thing you need to do is to draw a point onto that image at a certain latitude and longitude.

What you need is custom overlays, available in iOS 4 and up. The best place to find out about custom overlays is the WWDC 2010 video called "Session 127 - Customizing Maps with Overlays". There is also custom code available for the video. In the video, the presenter creates a custom map and embeds it in an MKMapView. He also describes a tool which you can use to make your tiles (to cut them up, get their shapes into the Mercator projection and name them properly). His map is scanned from a marine map, then placed on top of the normal map view.

You would be able to use boundingMapRect to create a bounds rectangle by converting your custom map's bounds to points. You can convert between points and coordinates using MKMapPointForCoordinate and MKCoordinateForMapPoint.

As for getting a point drawn on the map, you can do this a couple of ways. The easiest is to just use a custom MKAnnotationView with a dot as its image. This way the image doesn't grow and shrink as you zoom in. If you want the dot to grow and shrink, you should use a custom overlay for that too. You could easily use an MKCircleView, which is a subclass of MKOverlayView

For an arrow, you could use a normal view and rotate it (and place it on one side of the screen) according to the direction of your out-of-bounds point. Use MKMapPointForCoordinate and then calculate the directtion from the centre of your view.

But your best source is going to be that video. He goes into great depth about the whole process and gives source for a working app which is 90% of what you need for your own map.