Android Question Polygon Geofences

attenzi0ne · Oct 30, 2014

Hello everyone

Anyone have any examples on how to create a polygonal geofence?

warwound has a library that can create circula geofences but not polygonal
http://www.b4x.com/android/forum/th...es-stuff-like-low-power-location.29700/page-3

any help will be appreciated
regards

warwound · Oct 30, 2014

Look at the documentation for the android Geofence.Builder class:
https://developer.android.com/reference/com/google/android/gms/location/Geofence.Builder.html

You can only create a circular geofence.

Martin.

attenzi0ne · Oct 30, 2014

yes I have read your thread and the Geofence.Builder class page in detail and I am aware of that it only does circle

I researched a little bit, it can be accomplished with ray-casting alogrithm
http://rosettacode.org/wiki/Ray-casting_algorithm

anyone has ever done this before?

attenzi0ne · Oct 30, 2014

ok for anyone interested, I have created a library to findout if a given latlng is within a polygon.

everything is built upon warwounds polygon example on this thred:
http://www.b4x.com/android/forum/threads/google-maps-android-v2-tutorial.24415/page-3

B4X:

-
      Dim Point1, Point2, Point3, Point4, Point5 As LatLng
      Dim Points As List
 
      Points.Initialize
 
      '   points must be ordered in a  counterclockwise order
      '   (i found FillColor will fail if not correctly ordered)
 
      Point1.Initialize(52.756, 0.400)
      Points.Add(Point1)
      Point2.Initialize(52.417, 0.753)
      Points.Add(Point2)
      Point3.Initialize(52.638, 1.291)
      Points.Add(Point3)
      Point4.Initialize(52.902, 0.617)
      Points.Add(Point4)
      Point5.Initialize(52.756, 0.400)
      Points.Add(Point5)   '   closes the path

Points is a list of all the coordinates of our polygon

you can now use my library to check if we are inside or outside of the polygon

B4X:

_
    Dim c_raycast As PolygonRaycast
    Dim current_location As LatLng
   
    current_location.Initialize(52.902, 0.617)
    c_raycast.Initialize
    Log(c_raycast.f_check_current_location(current_location, Points))

it will return true if we are in and false if we are out

I hope it helps someone

Harris · May 11, 2015

Dim current_location As LatLng

What type of object is LatLng?
Can I create this without have to load another lib?

I just want to use PolygonRaycast as a stand alone...

Thanks

Troberg · May 12, 2015

The algoritm for finding out if a point is within a polygon is pretty straightforward:

Pick a point that you know is outside the polygon (such as the smallest X and smallest Y, both -1). Then, simply see how many polygon border lines a line between that point and the point you want to test intersects. If it's odd, it's inside, if even, it's outside. Think of it like this: If you walked from the reference point to the test point, each time you jumped over the fence, you would alternatingly jump inside and jump out.

The math to see if two lines intersect is pretty strightforward, but I don't have it in my head. Just google that bit.

Harris · May 12, 2015

Troberg said:
The algoritm for finding out if a point is within a polygon is pretty straightforward:

Pick a point that you know is outside the polygon (such as the smallest X and smallest Y, both -1). Then, simply see how many polygon border lines a line between that point and the point you want to test intersects. If it's odd, it's inside, if even, it's outside. Think of it like this: If you walked from the reference point to the test point, each time you jumped over the fence, you would alternatingly jump inside and jump out.

The math to see if two lines intersect is pretty strightforward, but I don't have it in my head. Just google that bit.

The math is in the lib in post 4 above. It is derived from the link in post 3 above.
I just wanted to know the object type of LatLng so I could use the lib directly.

I have a project where I shall use a table containing many geo-zones. When in any zone, the speed of the vehicle shall be noted. If speed is above the value set for the zone, a violation record is created.

Thanks

Harris · May 12, 2015

B4X:

<root>
  <doclet-version-NOT-library-version>1.00</doclet-version-NOT-library-version>
  <dependsOn>googlemaps</dependsOn>
  <dependsOn>googlemapsextras</dependsOn>
  <dependsOn>polygonraycast</dependsOn>
  <dependsOn>google-play-services</dependsOn>
  <class>
    <name>cyprustech.hunter.polygonraycast</name>
    <shortname>PolygonRaycast</shortname>
    <owner>process</owner>
    <method>
      <name>IsInitialized</name>
      <comment>Tests whether the object has been initialized.</comment>
      <returntype>boolean</returntype>
    </method>
    <method>
      <name DesignerName="Class_Globals">_class_globals</name>
      <returntype>String</returntype>
    </method>
    <method>
      <name DesignerName="f_check_current_location">_f_check_current_location</name>
      <returntype>boolean</returntype>
      <parameter>
        <name>ll_current_location</name>
        <type>anywheresoftware.b4a.objects.MapFragmentWrapper.LatLngWrapper</type>
      </parameter>
      <parameter>

I opened the XML for the lib.
Looks like the lib depends on Google Maps which contains the MapFragment.LatLng wrapper.

I guess (as suggested) I shall write my own routine based on code in link from post 3 above.

Thanks

Android Question Polygon Geofences

attenzi0ne

Member

warwound

Expert

attenzi0ne

Member

attenzi0ne

Member

Attachments

Harris

Expert

Troberg

Well-Known Member

Harris

Expert

Harris

Expert

Android Question Polygon Geofences

Member

Expert

Member

Member

Attachments

Expert

Well-Known Member

Expert

Expert

Privacy & Transparency

Privacy & Transparency