VERTCON for Google Earth (VERGE)
This page describes a free application that runs in
the Google Earth desktop client. Please install
and return to this page to learn more.
VERGE is a graphical front end for the NGS online tool, VERTCON,
that eliminates the need to input geodetic coordinates and displays the converted
height and datum shift in a placemark balloon. Both NGVD29-to-NAVD88 and
NAVD88-to-NGVD29 orthoheight conversions are supported.
Default input height is provided by the Google
API as an approximation of NAVD88 orthoheight.
Position the point of interest (POI) in the center of the view. One way to
do this is to double-click an unmarked location. To precisely position the
POI in the center of the view, add a placemark at the desired location;
then edit the properties of that placemark and reset the view
For best results, disable automatic tilting (Tools, Options, Navigation,
Do not automatically tilt while zooming) and minimize elevation
exaggeration (Tools, Options, 3D View, Elevation Exaggeration, 0.01).
Check the box beside the Orthoheight Conversion network link.
A form will be presented with read-only coordinates corresponding to
the view center and input fields for height and datum. Converted height
and datum shift are displayed when the Convert button is pressed.
On subsequent uses, reposition the POI and ensure that the network link
is checked and selected. Then choose Refresh from the Edit menu, or right-click
and select Refresh in the context menu
Coverage is limited to the conterminous United States. Check the Extents
display the coverage area bounding box.
Note: To save VERGE results from one Google Earth session to another, right-click
on Saved Placemarks and select Save to My Places or Save Place As.
All data are retrieved from remote servers. Data errors,
accuracy, and availability are beyond the control of this application.