Google Earth Tutorial: Polygons
Geobrowser
The following are
notes on my GTI presentations about how to create Polygons in Google Earth. If
you have questions please add a reply to this post and I respond as soon as I
can (if someone else doesn’t answer first!) -JB
(1) What is a Polygon?
A "polygon" in Google Earth is a series of vertices tessellated together to
form the borders of a solid shape. In the KML code is a member of the
<Placemark> family.
(2) Creating Paths
There are a number of ways to add KML objects in Google Earth. The three
simplest methods to create a Polygon are:
(1) Use
the menus (Add -> Polygon)
(2) Click
on the icon (showing an irregular hexagon) in the toolbar
(3)
Right-click on the folder in the Sidebar and select Add -> Polygon
When the dialog box appears move the cursor into the 3D Earth browser, and
click on the globe to create vertices. These will automatically become
connected by line segments the space between them filled white.
To change the thickness/color/opacity of the Polygon select options under the "Style, Color" tab in the dialog box. These settings can be changed for the
boundary line and/or Polygon fill.
In "Style,Color" under "Area" there is a drop-down menu option to show just the
boundary line (Outlined), just the
fill (Filled) or both (Filled + Outlined)
(3) Editing Polygons
To edit a Polygon reopen the dialog box by selecting the Polygon in the sidebar (click on it so it is highlighted in light blue) and right-click (ctrl-click on Mac). Select Properties (PC) or Get Info (Mac) at the bottom of the menu.
The dialog box will appear and the vertices defining the boundary will appear in the 3D browser as square red dots.
To Select a Vertex for Editing - Roll the cursor over the chosen vertex (it will turn green) and left-click on the vertex (it will turn blue)
- To Delete a Vertex – Select a vertex (see above) and press delete (or backspace).
- To Move a Vertex – Select a vertex (see above). Hold down the left-click and drag the
vertex to a new location.
- To Add a Vertex – Select a vertex (see above) in at the segment of the Polygon’s boundary to add vertices to, and click in the 3D browser.
(4) Creating 3D structures
Open the dialog box and select the "Altitude" tab. In the drop down menu change
Clamped to ground to Relative to ground, and make the
Altitude a value, e.g., 1000m. Note: In mountainous terrain not all the Polygon
will appear above the landscape if it is not raised high enough.
To create sides, select Extend path to ground. The color of these sides can now be changed under the "Style, Color" tab (the values for "Area").
This a simple 3D shape. More complex shapes, that can be have textures applied require the use of <Model> another type of KML <Placemark> that is best created through the use of SketchUp.
KML Examples
Google Campus – polygons with different colors, opacities and altitudes
delineate buildings at Google’s Mountain View Campus
Animated US States – Translucent Polygons used to map the 50 US States.
This file is animated using the KML Time Primitive, so when opened the time slider appears at the top of the left of the browser window. On pressing play, the polygons will appear according to the chronological order that the states joined the union.
Polygon (State) names will appear when zooming in.
The polygons are clickable – this will display description balloons with information on each state.
(modified from work by Brian Flood, http://www.arc2earth.com/)
