VERTICAL DATUMS: INTRODUCTION AND SOFTWARE REVIEW
A practical introduction to the issues of vertical datums and vertical coordinate systems in the geospatial sciences. This is followed by more detailed information on how vertical coordinate systems are represented in EPSG, OGC Well Known Text and other coordinate system definition systems. This leads into a survey of vertical coordinate system implementations in existing open source and proprietary software systems. Finally we close with details on improvements in vertical coordinate system support in PROJ.4,
GDAL, libgeotiff, and liblas based on work in 2009 and 2010 with concrete examples of how to utilize existing capabilities.
Frank Warmerdam - OSGeo