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Google Earth General

Google Earth is a powerful tool for viewing, creating and sharing GIS data. The latest improvements in the KML format allow storing attributes which makes possible exchange and even editing of GIS data using Google Earth.  Google Earth comes in four different versions (from Free to Enterprise). Make sure to read the Google Earth license agreement  before using it.

What is KML:

Keyhole Markup Language (KML) is an XML - based language for managing the display of geo spatial data in Google Maps and Google Earth. Since a KML file is a text file, its size might become quite large. Google Earth also takes a lot of RAM when large KML files are loaded. If possible split your datasets to subsets before converting them to KML. 

What is KMZ

The compressed version of the KML with the extension KMZ. Actually this is a zipped archive and the contents can be extracted with any zip program. A KMZ file can contain one or more KML files together with images etc. The export function of ET GeoWizards expect a full file name (with the extension). The extension of the output file defines whether the file will be compressed (KMZ) or not (KML)

The Import Export functions use the free Info-ZIP software to create and read KMZ files. The Info - Zip license is available here.  

Google Earth version

ET GeoWizards exports KML version 2.2 files (this is the KML version which introduced support for attributes called in KML "extended data"). Since it is impossible to find out which exactly version of Google Earth starts supporting KML 2.2, we recommend using Google Earth 4.2 or above.

Google Earth projection

For its reference system, KML uses Geographic Coordinate System (GCS) with WGS84 datum. In ArcGIS this projection is called GCS_WGS_1984.   The export to Google Earth functions of ET GeoWizards project the data on the fly to GCS_WGS_1984. If the source data is in a projection that have different datum, the functions of ET GeoWizards do on the fly geographic transformations on the data. 

• If the input data does not have a projection associated with it or have so called "Unknown" coordinate system, the data cannot be exported to KML.
• If the export functions cannot find an appropriate geographic transformation to project the input data to GCS_WGS_1984, they will not export the data. This might happen if  the input data is in a very specific or outdated projection.

Consideration when exporting to Google Earth

1. A single KML file can contain several feature classes of different types (Point, Polyline and Polygon). The Export To Google Earth function of ET GeoWizards structure the data in the following manner:

   • Each layer his its own folder
   • If  a layer is classified each class will have a subfolder
   • If the info points have been exported, the label points folder will follow the folder of the layer

   ArcMap layers structure	Google Earth folders structure

2. Google Earth does not allow identifying on the map Polyline and Polygon features.  The export functions of ET GeoWizards allow creating Info Points for each Polyline and Polygon features. These Info Points are created as follows:
   • For polygons - the label points of the polygons.
   • For polylines - the middle point of the polyline

   Using Info Points allows the attributes or description of polygon and polyline features to be displayed  by clicking on the appropriate Info Point in the Map window of Google Earth. Note that Google Earth allows displaying of either the Description or the Attributes. If a feature has a description the attributes cannot be displayed.

3. Point Symbols. ET GeoWizards uses a set of the standard Google Earth marker symbols to display point features. The user can select the marker to be used for each feature class. The symbols that can be used are:

   

   The size and the color of the symbols are taken from:

   • Export To Google Earth GUI function - The symbols assigned in the map
   • Feature Class To Google Earth scripting and toolbox function
     • Size - assigned by the user
     • Color - randomly assigned
4. Exporting elevations: The export functions of ET GeoWizards allow three ways of exporting Z values for the features.
   • Z values from geometry - Only available if the exported dataset to be exported has Z values (PointZ, PolylineZ, PolygonZ).
   • Z values from a field - A numeric field is required
   • Constant Z values for all features

   Note that Google Earth uses elevation values in Meters. If the Z values of the dataset are in Feet, the user needs to indicate this in the export procedure.

5. Representation of the elevations in Google Earth:
   • Z Type - how the Z values will be interpreted by Google Earth
     • Absolute - Sets the altitude of the coordinate relative to sea level, regardless of the elevation of the Google Earth terrain beneath the feature.
     • Relative - Sets the altitude of the feature relative to the Google Earth terrain in a particular location.
     • NONE  - the Z values are ignored - the feature will be displayed on the Google Earth surface
   • Extrusion - Specifies whether to connect the geometry to the ground.

   In the Export To Google Earth GUI function a single parameter is used to assign both values:

   • Absolute|0 - absolute Z Type. No extrusion
   • Absolute|1 - absolute Z Type. The geometries will be extruded to the terrain
   • Relative|0 - relative to the terrain Z Type. No extrusion
   • Relative|1 - relative to the terrain Z Type. The geometries will be extruded to the terrain
   • NONE - the geometries will follow the terrain
6. Attributes. The export functions of ET GeoWizards allow exporting the attributes of the feature classes to the KML file. In such a way the attributes can be displayed in Google Earth. There are several options that can be used:
   • Features - the attributes will be exported to the actual features
   • Labels - the attributes will be exported to the Info - Points
   • Both - the attributes will be attached to both, the actual features and the info points
   • NONE - no attributes will be exported.
7. Editing attributes in Google Earth. The attributes cannot be edited in Google Earth. The only way to edit attributes and send them back to ArcGIS is to use the Name and the Description of the Google Earth features.

• Google and Google Earth are trademarks of Google Inc
• All ESRI products mentioned are trademarks of Environmental Systems Research Institute, Inc.