Mobile Device Features 2

Compass

• Certain devices have a built in compass sensor.

• If they do, they call the ondeviceorientation() function when the compass reading changes.

• An event object is passed to the function with the compass reading in evt.webkitCompassHeading.

function window_ondeviceorientation(evt)
  TextBox1.value=evt.webkitCompassHeading
End function

• The Compass sample uses this information to rotate an image of a compass.

• The webKitTransform function rotates an image efficiently.

pos="0"

function window_ondeviceorientation(e)
  imgCompass.style.webkitTransform="rotate(" & pos & "deg)"
  pos = e.webkitCompassHeading
  imgCompass.style.webkitTransform="rotate(-" & pos & "deg)"
End function

Geolocation

geolocation.jpg

• Geolocation uses GPS sensors to return the current location of the device.

• The watchPosition() function sets the frequency of the Geolocation events.

• When a Geolocation event is triggered, the function named in the watchPosition function is called.

• The following data is passed to the event:

location.coords.longitude	The current longitude of the device. GPS required.
location.coords.latitude	The current latitude of the device. GPS required.
location.coords.altitude	The height of the location. GPS required.
location.coords.accuracy	The accuracy of the location. GPS required.
location.coords.altitudeAccuracy	The accuracy of the altitude. GPS required.
location.coords.heading	Degrees clockwise from North. GPS required.
location.coords.speed	Speed, meter per second. GPS required.
location.coords.timestamp	time and date of the observation. GPS required.

• Here's the code to start generating geolocation events:

Dim gps
function btnStart_onclick()
  options={timeout: 5000, maximumAge: 5000, enableHighAccuracy: True}
  gps=navigator.geolocation.watchPosition(onGeolocation, errorCallBack, options)
End function

• This code will call onGeolocation every 5 seconds.
• If GPS data cannot be obtained, the errorCallBack function is called.
• Cancel it by executing:

  navigator.geolocation.clearWatch(gps)

• Here's what the onGeolocation looks like. It gets called every 5 seconds.

function onGeolocation(location)
  Dim s
  s = "Longitude: " + location.coords.longitude & vbCRLF
  s = s & "Latitude: " + location.coords.latitude & vbCRLF
  s = s & "Speed: " + location.coords.speed & " " 
  s = s & "Altitude: " + location.coords.altitude & vbCRLF
  s = s & "Accuracy: " + location.coords.accuracy & " "
  s = s & "Accuracy(altitude): " + location.coords.altitudeAccuracy & " " & vbCRLF
  'Convert timestamp if needed.
  if IsNumeric(location.timestamp) Then
    gpsDate=new Date(location.timestamp)
  else
    gpsDate=location.timestamp
  End if
  TextArea1.value = s & "Timestamp: " + gpsDate
  ShowMap(location.coords.latitude, location.coords.longitude)
End function

• This function displays the GPS results in a TextArea.
• The code has to deal with the problem of different browsers returning timestamp in different formats.
• The ShowMap() function near the end displays a map from Google Maps.

function ShowMap(latitude, longitude)
  if SysInfo(10)-lastRefresh<10000 Then Exit function
  lastRefresh=SysInfo(10)
  s = "'https://maps.google.com/maps/api/staticmap?center=" & _
  latitude & "," & longitude & _
  "&zoom=14&size=300x200&maptype=roadmap&sensor=true&output=embed'"
  Map.innerHTML="<img width=300 height=200 src=" & s  & "></img>"
End function

• This function displays a Google map.
• The map is updated every 10 seconds
• More info on Google maps here: http://code.google.com/apis/maps/documentation/staticmaps/
• We pack the latitude and longitude into a URL query string.
• We display the results of the URL in an HTMLview.