Tuesday, January 29, 2008

Create Your Own Google Earth Application

Building an application to work with Google Earth is pretty easy to do. This article will walk through the creation of a very simple application to capture different views in Google Earth.

To begin with, you will need to download Microsoft's Visual Studion Express Edition for C# (available for free at http://www.microsoft.com/express/vcsharp/).

Once Visual Studio is installed, select 'New Project' from the 'File' menu. In the New Project dialog box, select 'Windows Forms Application' and name your application 'FirstGeApp' (see below). Then select OK.

Once the new form is visible, right click on it and select 'Properties'. A properties window should appear in the lower right hand corner of Visual Studio. Change the following Form properties:

Name = frmViewCapture

Text = View Capture

TopMost = True

The TopMost property will keep your form on top of all other applications. This works well when interacting with Google Earth.

Once you have set the Form properties, we will add a MenuStrip control to the form, to do this, click on the Toolbox on the left side of the Visual Studio. When the tools appear, click on the pushpin icon to keep the tools open (see above).

After this, look for the 'MenuStrip' control and drag it onto your form.

Once the MenuStrip is on your Form, click on it to enter text. In the example below, I have added a 'File' menu and a "Capture View" menu. You can keep the default setting for both of these.

Next, we are going to add a TreeView control to store our captured views. Find TreeView from the Toobox pallete and drag it onto the form. Once you have done so, change the 'Dock' property of the TreeView to "Fill" (see bel0w). This will make the TreeView take up our whole Form.

Next, add an ImageList control. You can drag this control onto the Form, or drag it to the bottom part of Visual Studio (see below).

After you have added the ImageList, right click on and select 'Choose images' (see above). In the next dialog box, select "Add". Navigate to an icon of your choice (I used
C:\Program Files\Google\Google Earth\GoogleEarth.ico).

Once you have added the image, click on the TreeView in the form and look in the Properties on the right. Set the following properties:

ImageList = imageList1
ImageIndex = 0

Next, you will need to add a reference to Google Earth. To do so, look for 'References' in the Solution Explorer in the upper right hand panel of Visual Studio. Right click References and select "Add Reference". In the dialog box that comes up, select the 'Browse' tab. Browse to
C:\Program Files\Google\Google Earth\googleearth.dll (depending on your installation) and add it as a reference.

Next, click on Form1 in the Solution Explorer and select Code View (see below).

Now we are going to add some code. You will see code similar to below. Add the underlined code to project.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace FirstGeApp
public partial class frmViewCapture : Form
//Add a reference to the Google Earth Library
private EARTHLib.ApplicationGEClass _ge = new EARTHLib.ApplicationGEClass();
//Make an integer to keep track of our Google Earth Views
private int _viewNum = 0;

public frmViewCapture()

Next, we will nee an event handler to capture the view. The simplest way to do this is to go back to your form and double-click "Capture View" on the menu that you added to your form. Visual Studio will automatically add the code below to handle the click event for this menu item.

private void captureViewToolStripMenuItem_Click(object sender, EventArgs e)


Next, we will add some code to actually handle this event. Write the following method underneath the captureViewToolStripMenuItem_Click method.

private void captureGeView()
//Get the current Google Earth Camera
EARTHLib.CameraInfoGE cam = _ge.GetCamera(1);
//Increment the number of views
//Create a Node for the tree view
TreeNode node = new TreeNode("View " + _viewNum.ToString());
//Add a reference the the GE Camera to the node
node.Tag = cam;
//Add the node to the tree view

Now, add "captureGeView();" to the captureViewToolStripMenuItem_Click method.

The next step is to add code to actually move Google Earth to each of the capture views. Go back to the Form and click on the TreeView control (treeView1). On top of the properties box, you will see an icon that looks like a bolt of lightening. Select this to see events for the TreeView. Double Click on MouseDown to automatically add a handler (see below).

This will add a "treeView1MouseDown" method to your code. Add the following code in this method.

private void treeView1_MouseDown(object sender, MouseEventArgs e)
//Get the clicked node
TreeNode node = this.treeView1.GetNodeAt(new Point(e.X, e.Y));
if (node != null)
//Get the cam from the tree view tag reference
EARTHLib.CameraInfoGE camera = (EARTHLib.CameraInfoGE)node.Tag;
//Move the GE View

And the following

private void moveGE(EARTHLib.CameraInfoGE cam)
//Set the Google Earth Camera View

_ge.SetCamera(cam, .5); //Change this number to alter your speed

Now Press F5 on your keyboard to run. Google Earth will open with your application. Clicking "Capture View" will add a view to your Tree View. Clicking on a node on your TreeView will move you to that node

Can you name this stadium?

You can take this much farther by adding user input to name each view and alter the speed. Chain them together to creat a tour or export to KML.

Monday, January 28, 2008

Build Your Own Google Earth Control

If anyone is interested in writing your own Google Earth Control that can be embedded in your applicaiton, there is good information on how to do so using C# at Google Groups for KML.

Also, you can see delphi code to do the same thing at googleearthairlines.

Monday, January 21, 2008

Create a Google Earth Toolbar / Form

A third option for integrating customized tools with Google Earth is pretty simple, you just write an application that hovers over Google Earth. It just like a floating tool bar or form that you can use to access your custom applications.

In the sample below, the application is sized to look like an extension to the Google Earth toolbar. It keeps track of the location of Google Earth so that it can stay in the same location. Different applications that interact with Google Earth can be launched from this toolbar.

Notice below the extension to the Google Earth Toolbar.

As an example, a custom Spatial Bookmark tool can save the current view of Google Earth for quick reference. Notice below how when this button is clicked on, a drop down menu of options is presented.

After selecting 'Create', a Windows form is launched. This form lets users name the current bookmark and set the zoom-to speed for when it selected.

Any of a number of spatial bookmarks can be save and accessed from the drop-down menu (see below).

The bookmark data itself is saved locally as an XML document. Different XML spatial bookmark documents can be saved and managed (see below).

In addition to saving bookmarks, the view itself can be sent through a web service to other people participating in a shared Google Earth collaboration.

Embed Google Earth Into Your Application

This method for customizing the Google Earth Interface, embedding the Google Earth render window (the actual map window) into your own applications, was apparently pioneered Luca Rocchi and his Google Earth Airlines application. Luca figured out that you could grab the GE map window using its Windows handle to place it into your own application. He has used this to plop GE into web applications, but the ActiveX control that he provides for free can also be used in any COM compliant language (such as VB.Net or C#). I have used this plugin (and a similar one of my own design) to access external applications from Google Earth.

This method lets you completely encapsulate Google Earth with your own tools. However, it also hides the Google Earth tools. To get around this, you can assign the entire Google Earth application to be a child to your own custom application. Interestingly, not too long after Luca released his 'Google Earth Airlines' plugin, Google provided a method in their API to directly access the Windows Handle of both the render window (actual map) and the application window (the full application).

Custom Google Earth Applications with Network Links

As posted previously, there are five general ways in which to provide custom control to Google Earth.

  1. Use built-in network links and server side scripting to serve custom data dynamically.
  2. Embed the Google Earth render window into your own application.
  3. Build customized applications that always hover over Google Earth.
  4. Use JavaScript in the built in web browser.
  5. Use a Flash application in a pop-up balloon.
Using this first option does not really use the API, nor does it really let you modify the user interface. It uses the very flexible, built-in, KML capabilities that the Google Earth client provides for free.

To use it, you need to have a web server that can respond to a network link request from Google Earth. The request can have a number of client parameters in it, such as the view information. This can be used to generate a return KML document whose content is based on the area that a user is looking at. A network link KML file can be added to Google Earth that sends this request to update the KML document on a time basis, or whenever the user zooms and stops.

This method can get pretty sophisticated. The Regions KML tag allows users to define the visual region of interest for specified data in the KML document. This is a great way to handle very large datasets.

A network-link KML document can be created that defines a number of different, thematic, KML documents, which can be loaded and unloaded every time the user enters a defined region. Brian Flood offers an excellent example of how this can be applied to large geospatial data sets using Arc2Earth.

Customizing the Google Earth Interface

Ever since people became aware that it was possible to allow external software applications to interact with Google Earth using their API (which seems to be in perpetual beta stage), they have been trying to figure out how best to integrate their custom applications into Google Earth.

While almost all of the initial efforts dealt with taking existing applications and simply loading their data into GE in a KML format, later efforts involved trying to make all functionality directly accessible form the Google Earth application itself.

The basic problem, however, is that Google Earth does not provide a framework to extend its user interface. You cannot simply add a new button to their toolbar that fires off your own application, as you can in many GIS and Office software packages.

A couple of tricks have been developed to make Google Earth application extensions appear to work seamlessly with Google Earth. They generally fall into five categories.

  1. Use built-in network links and server side scripting to serve custom data dynamically.
  2. Embed the Google Earth render window into your own application.
  3. Build customized applications that always hover over Google Earth.
  4. Use JavaScript in the built in web browser.
  5. Use a Flash application in a pop-up balloon.

Has anyone come up with their own way get their application to work with Google Earth?

Thursday, January 10, 2008

Publish Your Own Google Map Without a Server

If you would like to publish your own Google Map, but do not have a server to place it on, there are some greate options to get you started without needing a server.

I ran across this web page recently that has a number of excellent tutorials for using Google's Page Creator. The Google Pages site is fantastic for putting together really quick and easy web pages. It also will let's you publish your own Google Maps Web Page using the this tutorial.

I used this tutorial to put together my own sample Google Map. This is pretty basic, but could be spiced up quite a bit with added funtionality.

Saturday, January 05, 2008

Creating Hybrid Spatial Solutions: Commercial and Open Source

Open source geospatial systems and tools have really taken off in recent years, as has the open source community at large. While an open source geospatial solution may be enticing to some GIS managers, there remain a number of hurdles for them to be effectively employed.

Chief among these hurdles are the lack of documentation, training, and the added difficulties of configuring or extending open source solutions (it’s tough to get a good ArcSDE administrator, it’s tougher still to get a good PostGIS administrator). In addition to this, while open source is starting to provide a rather comprehensive suite of software that includes desktop and web based GIS tools and services, as well as database storage and support, they still tend to lack a good data management framework. I suspect that the reason for this is because developers of open source spatial software want their work to be able to do something relatively fast. So they tend to make them work on existing GIS data (such as shapefiles) rather then put a heavy emphasis on creating and managing spatial data from scratch.

Most GIS may be reluctant to move too quickly towards an open source solution when they already have a functionally proprietary system in place. Even though moving towards open source may be compelling due to the potential cost savings in licensing fees, those savings are offset by concerns over being able to manage the system and maintain current capabilities.

The most likely scenario in the near future is to start seeing the appearance of hybrid solutions.

As an example, a GIS shop may decide that their use of ArcEditor (or ArcInfo), ArcSDE and ArcIMS (or ArcServer) may be overkill for their specific requirements. While this software provides an enormous amount of capability, this may not actually be required. It may be possible for them to effectively manage their spatial data using an ArcMap license to manage the spatial data, and then have that data pushed into a PostGIS database for corporate or enterprise attribute editing and visualization. The key is to leverage the power of both commercial and open source solutions towards cheaper and oftentimes more powerful solution.