Hi
So my aim is to draw a grid on the map for maidenhead locator grid, the grid system at world level is 20 degrees longitude and 10 degress latitude.
The grid changes at two further levels for country and local area.To draw the grid once there is would be too many polylines and the app would crash. So the idea is to use the visible rectangle area changed on the mapview.
I have implemented this just for longitude lines at the moment and have noticed three things
1 Drawining a vertical polyline at 180 longitude from -90 to 90 latitude the line can appear and disappear when viewing at different zoom levels or just panning around.
2 Drawining any polylines across - longitude to a + longitude the line fails to be drawn and not visible it needs to be drawn only from - to 0 and from 0 to + longitudes
3 The following code below draws the longitude lines for the top level maidenhead grid, however the lines dissapear and appear and flicker.
Below is the code I have implemented
func mapViewDidChangeVisibleRegion(_ mapView: MKMapView) {
DispatchQueue.main.async {
let zoomLevel = mapView.getZoomLevel()
if(mapView.overlays.count > 0)
{
for line in mapView.overlays
{
mapView.removeOverlay(line)
}
}
let northEast = mapView.convert(CGPoint(x: mapView.bounds.width, y: 0), toCoordinateFrom: mapView)
let southWest = mapView.convert(CGPoint(x: 0, y: mapView.bounds.height), toCoordinateFrom: mapView)
let minLon = 10 * Int((floor(southWest.longitude) / 10.0).rounded())
let maxLon = 10 * Int((floor(northEast.longitude) / 10.0).rounded())
let minLat = 10 * Int((floor(southWest.latitude) / 10.0).rounded())
let maxLat = 10 * Int((floor(northEast.latitude) / 10.0).rounded())
if(zoomLevel < 6)
{
for latIndex in stride(from: minLat, through: maxLat, by: 10)
{
var pointsLon : [CLLocationCoordinate2D] = [CLLocationCoordinate2D]()
if(minLon < 0 && maxLon < 0)
{
let startPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(minLon))
pointsLon.append(startPos)
let endPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(maxLon))
pointsLon.append(endPos)
}
if(minLon > 0 && maxLon > 0)
{
let startPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(minLon))
pointsLon.append(startPos)
let endPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(maxLon))
pointsLon.append(endPos)
}
if(minLon < 0 && maxLon > 0 )
{
let startPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(maxLon))
pointsLon.append(startPos)
let midPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(0))
pointsLon.append(midPos)
let endPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(minLon))
pointsLon.append(endPos)
}
if(minLon > 0 && maxLon < 0 )
{
let sPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(maxLon))
pointsLon.append(sPos)
let mPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(-180))
pointsLon.append(mPos)
let polyline = MKPolyline(coordinates: pointsLon, count: pointsLon.count)
self.polylines.append(polyline)
mapView.addOverlay(polyline, level: .aboveRoads )
pointsLon.removeAll()
let startPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(minLon))
pointsLon.append(startPos)
let midPos = CLLocationCoordinate2DMake(CLLocationDegrees(latIndex), CLLocationDegrees(180))
pointsLon.append(midPos)
}
let polyline = MKPolyline(coordinates: pointsLon, count: pointsLon.count)
self.polylines.append(polyline)
mapView.addOverlay(polyline, level: .aboveRoads )
}
}
else if(zoomLevel < 12)
{
//to be implemented
}
else{
//to be implemented
}
}
}
I have been trying to workout why this does not render properly, is their something I am doing wrong in code or is their a better approach, or is their a bug in mapkit.
Any help would be greatly appreaciated as I am out of ideas.
Thanks in advance
Mark...
