Android Question Map: Diameter of circle displayed=screen width

toby · Nov 12, 2018

I want to adjust the zoom value according to a specified circle radius so that on the phone screen the circle covers the entire screen width, as the attached screenshot shows.

Here is where I'm stuck:

B4X:

'zoom in
    Dim zoom As Float=13 'how to calculate this value
                                     'so that the circle width is same or almost the same as screen width?
    Dim cp As CameraPosition
    cp.Initialize( latitude, longitude, zoom)
    gmap.AnimateCamera(cp)

Sample project attached.

TIA

toby · Nov 13, 2018

I've found some solution at https://stackoverflow.com/questions/9768439/how-to-google-map-circles-fit-the-map

B4X:

map.fitBounds(circle.getBounds());

It seems to me that they're not yet implemented in B4A.

Erel · Nov 13, 2018

Check this library: https://www.b4x.com/android/forum/threads/googlemapsextras.26277/#content

klaus · Nov 13, 2018

You could do it this way:

B4X:

Private VisibleWidth, degCircle, Ratio As Double
Private OriginalZoom, Zoom As Float
Private LatLngB As LatLngBounds
OriginalZoom = gmap.CameraPosition.Zoom
LatLngB = gme.GetProjection(gmap).GetVisibleRegion.LatLngBounds    'Visible region bounds
VisibleWidth = Abs(LatLngB.SouthWest.Longitude - LatLngB.NorthEast.Longitude) 'width of the visible region on the screen
degCircle = 360 / 40075000 * radius * 2 / CosD(latitude) ' circle diameter in degrees
Ratio = Logarithm(VisibleWidth / degCircle, 2)    'ratio visible width / circle diameter
Zoom = OriginalZoom + Ratio    'optimum zoom

EDIT: amended the code and the project according to post #5 and #6.

toby · Nov 15, 2018

Thank you @klaus for the code!

I tried it with different diameters (2000,5000,8000 & 10000) and the results I got are inconsistent. As shown in the attached screenshots, Diameter 5000 & 10000 gave me perfect results while the other two didn't. Did I miss something?

klaus · Nov 15, 2018

Change this line:
VisibleWidth = Abs(LatLngB.SouthWest.Latitude - LatLngB.NorthEast.Latitude)
to
VisibleWidth = Abs(LatLngB.SouthWest.Longitude - LatLngB.NorthEast.Longitude)

And this line, I had rounded the zoom to an integer value.
Ratio =Floor(Logarithm(VisibleWidth / degCircle, 2))
to
Ratio = Logarithm(VisibleWidth / degCircle, 2)

Sorry for the 'bad' solution.
I have updated the project and the code in post #4 and

toby · Nov 16, 2018

Ça fonctionne parfaitement! Merci beaucoup @klaus! I'm very impressed and you deserve a medal

!

Android Question Map: Diameter of circle displayed=screen width

toby

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Android Question Map: Diameter of circle displayed=screen width

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