A user-friendly implementation of the NGS VERTCON transformation from NGVD 1929 to NAVD 1988 vertical datums in the continental US.
The original VERTCON is developed by the US National Geodetic Survey. The source for that version (2.1) is available here. The NGS's web tool is here. The original VERTCON 2.1 README is included in this repository.
VERTCON represents the difference between the NAVD 1988 and NGVD 1929 datums. To go from NGVD29 -> NAVD88, add the value returned. To go from NAVD88 -> NGVD29, subtract the value. The value for a given point is bilinearly interpolated from the values of the surrounding cells.
Requires GDAL, python-gdal, NumPy and Flask.