VERTCON for Google Earth (VERGE)

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 Elevation API as an approximation of NAVD88 orthoheight.

1. 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 (explain). 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).
2. 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.
3. 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 (explain).

Image NGS

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.