Scale control

[1ec5]

Apple Maps (but not MKMapView itself) shows a scale (in both miles and kilometers) in the top-left corner of the map view while you pinch to zoom in or out. A scale would be a useful feature to bake into MGLMapView, either off by default or off except while you pinch. It would help to give context, especially since GL doesn’t snap the zoom level to increments and allows very high zoom levels.

[1ec5]

Correction: MKMapView.showsScale = YES turns on a persistent scale at the top-left corner.

[Bluezen]

Hi @1ec5 ! Do you know if there is a plan to add this feature in an upcoming release?

If not, how would you recommend me to proceed with the current iOS SDK 3.2.3 if I wanted to show a simple scale ?
Adding a custom UIView on top of the MKMapView which, on every Map position changes (-mapViewRegionIsChanging: -mapView:regionDidChangeAnimated: ), uses visibleCoordinateBounds (or something else ?) to extrapolate and update its display?

[1ec5]

We haven't scheduled this feature into an upcoming release yet, but we aren't opposed to getting the feature in if someone steps up with an implementation.

In the meantime, you have the right idea with the delegate methods (although you might find -mapViewDidFinishRenderingFrame:fullyRendered: to be more predictable). In terms of calculating the width of the scale's indicators, I'd use -[MGLMapView metersPerPointAtLatitude:], passing in the current center latitude.

If you come up with an implementation that you feel would be appropriate for the SDK, we'd be happy to consider your PR.

[Bluezen]

Thanks for pointing out -[MGLMapView metersPerPointAtLatitude:] and mapViewDidFinishRenderingFrame:fullyRendered !

Okay, if I am satisfied with my implementation I will propose a PR.

[friedbunny]

Somewhat relatedly, here’s a quick way to get the geographic distance spanned by the entire map view:

func mapView(mapView: MGLMapView, regionDidChangeAnimated animated: Bool) {
     let screenWidthInPoints = Double(mapView.bounds.size.width)
     let metersPerPoint = mapView.metersPerPointAtLatitude(mapView.centerCoordinate.latitude)
     let screenDistanceInMeters = Int(screenWidthInPoints * metersPerPoint)

     print("\(screenWidthInPoints) × \(metersPerPoint) = \(screenDistanceInMeters)m")
}

// Portrait iPhone 6++++
414.0 × 4.87247101190374 = 2017m
// Rotate to landscape
736.0 × 4.87247101190374 = 3586m

[1ec5]

This is GL JS parity issue now that mapbox/mapbox-gl-js#2940 has landed.

[1ec5]

An Android equivalent is being implemented in #6555.

[andrewstay]

Could you please update on the progress on this feature?

[frederoni]

Work towards this issue is happening in #7432

[1ec5]

The scale bar is being implemented in #7631.