Center / Zoom over Group of Markers on Databind

[Dan]

I am binding a set of addresses to the RadMap server-side, and would like to set the Zoom and CenterPosition so that the points on the map are all within view.

For instance, the user may have zoomed into the US - the selects a list that adds addresses in Europe.  I would like to reset the map zoom/center to show this whole group.  How would I go about doing this?

[Dan]

I have figured out how to center the Map over a series of Lat/Lng points - using their averages.  

I would like to figure out how to set the Zoom now - so that it fits all of the mapped points - but am not sure how to figure which zoom level to use?  If I find the greatest variances between Lat and Lng points - how would that relate to the Zoom level 0-19?  

A couple examples of the desired effect:

 - The user is zoomed in on Washington DC
 - The user selects a list of addresses in China
 - I would recenter the map based on the Lat/Lng coordinate averages
 - But how do I set the Zoom?

 - The user is at zoom level 2 - which seems to show the whole world map once.
 - They select addresses in Los Angeles
 - I would recenter the map based on the Lat/Lng coordinate averages
 - How would I figure the zoom to set the map to just show Los Angeles?

[Dan]

Some messing around + Googling, and this bit of code does the trick for me.

Hope this is helpful to someone else.

As a side note - this would be a nice thing to integrate into the RadMap control...

01.Protected Sub setMap(MappedNames As List(Of GeocodedAddress), map As RadMap)
02.
03.    Dim mapWidth As Integer = 1050
04.    Dim paddingFactor As Double = 1.2
05.
06.    Dim minY As Double = MappedNames.Min(Function(x) x.Latitude)
07.    Dim maxY As Double = MappedNames.Max(Function(x) x.Latitude)
08.    Dim minX As Double = MappedNames.Min(Function(x) x.Longitude)
09.    Dim maxX As Double = MappedNames.Max(Function(x) x.Longitude)
10.    Dim centerY As Double = (minY + maxY) / 2
11.    Dim centerX As Double = (minX + maxX) / 2
12.
13.    Dim minRadianY As Double = Math.Log((Math.Sin(Degree2Radian(minY)) + 1) / Math.Cos(Degree2Radian(minY)))
14.    Dim maxRadianY As Double = Math.Log((Math.Sin(Degree2Radian(maxY)) + 1) / Math.Cos(Degree2Radian(maxY)))
15.    Dim centerRadianY As Double = (minRadianY + maxRadianY) / 2
16.    centerY = Radian2Degree(Math.Atan(Math.Sinh(centerRadianY)))
17.
18.    Dim deltaX As Double = maxX - minX
19.    Dim resolutionX As Double = deltaX / mapWidth
20.
21.    Dim vy0 As Double = Math.Log(Math.Tan(Math.PI * (0.25 + centerY / 360)))
22.    Dim vy1 As Double = Math.Log(Math.Tan(Math.PI * (0.25 + maxY / 360)))
23.    Dim viewHeightHalf As Double = map.Height.Value / 2
24.    Dim zoomFactorPowered As Double = viewHeightHalf / (40.7436654315252 * (vy1 - vy0))
25.    Dim resolutionY As Double = 360.0 / (zoomFactorPowered * 256)
26.
27.    Dim resolution As Double = Math.Max(resolutionX, resolutionY) * paddingFactor
28.    Dim zoom As Double = Math.Log(360 / (resolution * 256), 2)
29.
30.    map.Zoom = Math.Floor(zoom)
31.    map.CenterSettings.Latitude = centerY
32.    map.CenterSettings.Longitude = centerX
33.
34.End Sub

[Ianko]

Hello Dan,

Thank you for sharing this useful method with the Telerik community.

Indeed such functionality would be very useful in the RadMap control. I logged this feature request, so that other users could vote for this suggestion also.

On a side note, it would be appreciated if you could extend the bellow example with some comments and also provide a simple, locally runnable project, so that it could be easily examined. This way I would be able to convert this thread into a Code Library and reward you with some Telerik points for the knowledge sharing.

Regards,
Ianko
Telerik