SEAMLESS HIGH RESOLUTION TOPOGRAPHIC MODEL OF THE CONTIGUOUS UNITED STATES DEPLOYED USING GOOGLE EARTH

Various governmental and private organizations provide LiDAR-generated imagery using web browsers or apps. In support of my ongoing Survey of ovoid basins in the lower-48 United States, a seamless High Resolution Topographic Model has been deployed using Google Earth as a viewing platform. Being integrated with this free and stable virtual globe has advantages over closed systems for integration into workflows. Ongoing efforts render the latest public LiDAR releases into the facility to insure a best effort 1 m resolution set. Recognizing not all the USA is currently available at 1 m resolutions, some areas are rendered at resolutions of 1.5 m, 3m or 10 m.

The implementation avails itself of Google Earth’s “Region” facility, assuring a responsive experience by limiting the requested image tiles to the user’s field of view. The facility is made available publicly by me under a Creative Commons Non-Commercial License. Attribution requested.

Models are assembled as quadrangles 1º of Longitude and 1º of Latitude - as currently described by the USGS - and is the top-most organizational element. To provide reasonable sized elements for LiDAR-quality models, each 1º footprint is subdivided into sixteen (16) 15 Minute (15' / 0.25º) quadrangles, each represented by a stacked-resolution set of ~200 raster image files.

The design goal is to aid in the visual identification and measurement of expansive landforms represented by sub-meter relief. The rendering uses a 10-meter cyclic color palette tuned to human perception. It yields a relative elevation value for the local relief as each color re-appears every 10 meters starting at sea level. A color-to-elevation legend is provided as a screen overlay, providing a relative index for the elevation values. The Google Earth elevation value is typically within a meter or two of the LiDAR-provided value, which should be referenced to advise the actual elevation above sea level. Model images are rendered with a 20x exaggeration for hill shade as an optical illusion of relief.

A small starter file is used to access the facility. When opened in Google Earth, a Google Earth Network Link downloads a control file from an Amazon S3 Cloud repository. Required control structures and model images are thereafter pulled from the cloud storage dynamically as the user’s view port zooms or moves across the terrain.