Question

I’m developing an application that’s tracing lines of highways on the Google Maps SDK Add-On.

There are a lot of points painted, which inadvertently make the Maps very sluggish to navigate. It seems iOS Maps take care of this issue, as a significant amount of points can be drawn without the maps becoming sluggish.

I started sampling points depending on zoom level. E.g. zoom level 7 only uses, and draws lines to, every 20th point to trace the route. But even that is still too many points and ends up with a very sluggish panning and zooming experience.

Two questions:

One: Is it possible to detect the current region of the map being displayed in the phone, and no longer paint points off-screen?

EDIT – after some initial investigation it’s easily possible to detect the clipping region and not paint points/lines. quickReject is the function I’ve used for this. It does not help too much with performance as all points are still being traversed to identify if they must be drawn – I’m sure it can be optimized.

Two: Is it at all possible to cache, perhaps the path, being drawn (this would have to be done per zoom level, I assume, due to the projection of the point?)

Answer 1

Is it possible to detect the current region of the map being displayed in the phone, and no longer paint points off-screen?

Yes, you can get the projection of the four corners of your screen :

Projection proj = mapView.getProjection();
GeoPoint topLeft = proj.fromPixels(0, 0);

GeoPoint bottomRight = proj.fromPixels(mapView.getWidth()-1, mapView.getHeight()-1);

double topLat = topLeft.getLatitudeE6()/1E6;
double topLon = topLeft.getLongitudeE6()/1E6;
double bottomLat = bottomRight.getLatitudeE6()/1E6;
double bottomLon = bottomRight.getLongitudeE6()/1E6;

While rendering, you should only select points that lie in these bounds.

See also :

• MapView with lazy loading
• Proper way of adding overlay items

In case you are at a very high zoom level see:

• Point clustering in MapView

Personally I’ve use route simplification algorithms to reduce the number of points on a straight path. For e.g if 20 points lie in the same line, it makes sense to use the start and end point and drawn a straight line.