KML for Google Earth: How to set Icon size to specific physical distance?

I have a collection of GPS data points with timestamps that I'm using to create an animation of a person's motion along a path. The GPS data also has an accuracy figure (in meters) that I'd like to represent on the map using the icon size. I'd like to have the Icon be a circle centered on the person's lat/long with a radius equal to the accuracy of the GPS measurement.

I've searched the forums/Google and can't find a way to specify icon in size in physical distance. Is there a way to do this? I've read about the <scale> attribute which allows you to resize an icon, but it's not obvious to me how you can calculate the right scale number to correspond to, say, 10 meters on the map. Does anyone have any experience creating icons of a specific physical size?

Solution

the icon sizing is to set the number of pixels.

another method is to use a model in your kml

https://developers.google.com/kml/documentation/kmlreference#model

this will be less computational intense than calculating your lon lats for the circle

create a simple size scale mode with Sketchup, a cylinder 1 meter in diameter

and you can use

 <Scale> 
    <x>1</x>                
    <y>1</y>               
    <z>1</z>               
  </Scale>

setting the x and y to the accuracy

an example A screen capture from Google Earth

the kml :

<?xml version="1.0" encoding="utf-16"?>
<kml xmlns="http://www.opengis.net/kml/2.2"
xmlns:gx="http://www.google.com/kml/ext/2.2"
xmlns:kml="http://www.opengis.net/kml/2.2"
xmlns:atom="http://www.w3.org/2005/Atom">
  <Document>
    <name>TestScaleSize</name> 
      <name>PathPoints</name> 
      <Placemark>
        <name>Point1</name>
        <TimeStamp> <when>2012-06-20T12:00</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26400</latitude> <altitude>0</altitude></Location>
           <Scale><x>8</x><y>8</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point2</name>
        <TimeStamp> <when>2012-06-20T12:01</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26405</latitude> <altitude>0</altitude></Location>
           <Scale><x>5</x><y>5</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point3</name>
        <TimeStamp> <when>2012-06-20T12:02</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26410</latitude> <altitude>0</altitude></Location>
           <Scale><x>4</x><y>4</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point4</name>
        <TimeStamp> <when>2012-06-20T12:03</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26415</latitude> <altitude>0</altitude></Location>
           <Scale><x>3</x><y>3</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point5</name>
        <TimeStamp> <when>2012-06-20T12:04</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26420</latitude> <altitude>0</altitude></Location>
           <Scale><x>2</x><y>2</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point6</name>
        <TimeStamp> <when>2012-06-20T12:05</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26425</latitude> <altitude>0</altitude></Location>
           <Scale><x>1</x><y>1</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
       <Placemark>
        <name>Point7</name>
        <TimeStamp> <when>2012-06-20T12:06</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26430</latitude> <altitude>0</altitude></Location>
           <Scale><x>1</x><y>1</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point8</name>
        <TimeStamp> <when>2012-06-20T12:07</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26435</latitude> <altitude>0</altitude></Location>
           <Scale><x>3</x><y>3</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point9</name>
        <TimeStamp> <when>2012-06-20T12:08</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26440</latitude> <altitude>0</altitude></Location>
           <Scale><x>1</x><y>1</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
      <Placemark>
        <name>Point10</name>
        <TimeStamp> <when>2012-06-20T12:09</when></TimeStamp>
        <Model>
          <altitudeMode>relativeToGround</altitudeMode>
          <Location><longitude>-123.145702</longitude><latitude> 49.26445</latitude> <altitude>0</altitude></Location>
           <Scale><x>1</x><y>1</y><z>1</z></Scale>
          <Link><href>scaleIcon.dae</href></Link>
        </Model>
      </Placemark>
  </Document>
</kml>

the xml for the model is as follows save it as "scaleIcon.dae" and have both in the same folder,

![<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<COLLADA xmlns="http://www.collada.org/2005/11/COLLADASchema" version="1.4.1">
    <asset>
        <contributor>
            <authoring_tool>Google SketchUp 8.0.11752</authoring_tool>
        </contributor>
        <created>2012-06-21T02:47:22Z</created>
        <modified>2012-06-21T02:47:22Z</modified>
        <unit meter="0.02539999969303608" name="inch" />
        <up_axis>Z_UP</up_axis>
    </asset>
    <library_visual_scenes>
        <visual_scene id="ID1">
            <node name="SketchUp">
                <instance_geometry url="#ID2">
                    <bind_material>
                        <technique_common>
                            <instance_material symbol="Material2" target="#ID3">
                                <bind_vertex_input semantic="UVSET0" input_semantic="TEXCOORD" input_set="0" />
                            </instance_material>
                        </technique_common>
                    </bind_material>
                </instance_geometry>
            </node>
        </visual_scene>
    </library_visual_scenes>
    <library_geometries>
        <geometry id="ID2">
            <mesh>
                <source id="ID5">
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                    <technique_common>
                        <accessor count="96" source="#ID8" stride="3">
                            <param name="X" type="float" />
                            <param name="Y" type="float" />
                            <param name="Z" type="float" />
                        </accessor>
                    </technique_common>
                </source>
                <source id="ID6">
                    <float_array id="ID9" count="288">0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 0 0 -1 -0.7071067811865475 0.7071067811865476 0 -0.4999999999999999 0.8660254037844387 0 -0.7071067811865475 0.7071067811865476 0 -0.4999999999999999 0.8660254037844387 0 -0.2588190451025206 0.9659258262890684 0 -0.2588190451025206 0.9659258262890684 0 2.673332968694072e-016 1 0 2.673332968694072e-016 1 0 0.2588190451025209 0.9659258262890682 0 0.2588190451025209 0.9659258262890682 0 0.5 0.8660254037844386 0 0.5 0.8660254037844386 0 0.7071067811865475 0.7071067811865476 0 0.7071067811865475 0.7071067811865476 0 0.8660254037844387 0.5 0 0.8660254037844387 0.5 0 0.9659258262890684 0.2588190451025206 0 0.9659258262890684 0.2588190451025206 0 1 -4.901110442605798e-016 0 1 -4.901110442605798e-016 0 0.9659258262890682 -0.2588190451025212 0 0.9659258262890682 -0.2588190451025212 0 0.8660254037844384 -0.5000000000000004 0 0.8660254037844384 -0.5000000000000004 0 0.7071067811865471 -0.707106781186548 0 0.7071067811865471 -0.707106781186548 0 0.4999999999999995 -0.8660254037844389 0 0.4999999999999995 -0.8660254037844389 0 0.2588190451025204 -0.9659258262890684 0 0.2588190451025204 -0.9659258262890684 0 -4.72288824469286e-016 -1 0 -4.72288824469286e-016 -1 0 -0.2588190451025212 -0.9659258262890682 0 -0.2588190451025212 -0.9659258262890682 0 -0.5000000000000004 -0.8660254037844384 0 -0.5000000000000004 -0.8660254037844384 0 -0.7071067811865479 -0.7071067811865471 0 -0.7071067811865479 -0.7071067811865471 0 -0.8660254037844388 -0.4999999999999998 0 -0.8660254037844388 -0.4999999999999998 0 -0.9659258262890684 -0.2588190451025205 0 -0.9659258262890684 -0.2588190451025205 0 -1 2.316888572868195e-016 0 -1 2.316888572868195e-016 0 -0.9659258262890682 0.258819045102521 0 -0.9659258262890682 0.258819045102521 0 -0.8660254037844386 0.5000000000000001 0 -0.8660254037844386 0.5000000000000001 0 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1 -0 -0 1</float_array>
                    <technique_common>
                        <accessor count="96" source="#ID9" stride="3">
                            <param name="X" type="float" />
                            <param name="Y" type="float" />
                            <param name="Z" type="float" />
                        </accessor>
                    </technique_common>
                </source>
                <vertices id="ID7">
                    <input semantic="POSITION" source="#ID5" />
                    <input semantic="NORMAL" source="#ID6" />
                </vertices>
                <triangles count="92" material="Material2">
                    <input offset="0" semantic="VERTEX" source="#ID7" />
                    <p>0 1 2 1 0 3 3 0 4 3 4 5 5 4 6 5 6 7 7 6 8 7 8 9 9 8 10 9 10 11 11 10 12 11 12 13 13 12 14 13 14 15 15 14 16 15 16 17 17 16 18 17 18 19 19 18 20 19 20 21 21 20 22 21 22 23 24 25 26 25 24 27 27 28 25 28 27 29 29 30 28 30 29 31 31 32 30 32 31 33 33 34 32 34 33 35 35 36 34 36 35 37 36 38 39 38 36 37 39 40 41 40 39 38 41 42 43 42 41 40 43 44 45 44 43 42 45 46 47 46 45 44 47 48 49 48 47 46 48 50 49 50 48 51 51 52 50 52 51 53 53 54 52 54 53 55 55 56 54 56 55 57 57 58 56 58 57 59 59 60 58 60 59 61 62 60 61 60 62 63 64 63 62 63 64 65 66 65 64 65 66 67 68 67 66 67 68 69 70 69 68 69 70 71 24 71 70 71 24 26 72 73 74 73 72 75 73 75 76 76 75 77 76 77 78 78 77 79 78 79 80 80 79 81 80 81 82 82 81 83 82 83 84 84 83 85 84 85 86 86 85 87 86 87 88 88 87 89 88 89 90 90 89 91 90 91 92 92 91 93 92 93 94 94 93 95</p>
                </triangles>
            </mesh>
        </geometry>
    </library_geometries>
    <library_materials>
        <material id="ID3" name="Color_A01_">
            <instance_effect url="#ID4" />
        </material>
    </library_materials>
    <library_effects>
        <effect id="ID4">
            <profile_COMMON>
                <technique sid="COMMON">
                    <lambert>
                        <diffuse>
                            <color>1 0 0 1</color>
                        </diffuse>
                    </lambert>
                </technique>
            </profile_COMMON>
        </effect>
    </library_effects>
    <scene>
        <instance_visual_scene url="#ID1" />
    </scene>
</COLLADA>][1]