Which transformer do I use to do 3D reprojection (vertical datums)?

Introduction

FME is able to reproject data vertically (height) as well as horizontally. FME has several reprojector transformers, each one has its own functionality depending on the spatial location of your data. For an in-depth look at these transformers and more information on coordinate systems, please see Working with Coordinate Systems in FME. 
 
If you are looking to reproject vertical datums, as of FME 2022.0, there are four transformers, the CsmapReprojector, the GridInQuestIIReprojector, the ReframeReprojector, and updated for FME 2022.0, the EsriReprojector. 
 

Vertical Reprojection Transformers

EsriReprojector

FME 2022.0 and newer now supports vertical datum reprojections. Start by selecting the same horizontal source and destination coordinate system, then enable the Vertical section. Next, select the source and destination coordinate system. Check out the 2022.0 Sneak Peek video for a demo. For more information, see the documentation. 

 

CsmapReprojector

The CsmapReprojector reprojects feature coordinates from one coordinate system to another using the CS-MAP library. The CS-Map library is FME’s default library, and so is generally used for most transformations unless using other library-specific transformers such as the EsriReprojetor. Using this transformer explicitly ensures that this library is used, and also provides options for handing Z (vertical) values. For an in-depth look at the vertical transformation parameters, please see the documentation. 

 

GridInQuestIIReprojector

The GridInQuestIIReprojector transformer can transform heights in Z values for Ireland Malin Head or Belfast. The GridInQuestIIReprojector uses the Grid InQuest library which is different from FME’s default, CS-MAP library. For more information on the GridInQuestIIReprojector, please see the documentation. 

 

ReframeReprojector

The ReframeReprojector reprojects feature coordinates from one coordinate system to another in Switzerland, using the Reframe library from the Federal Office of Topography (swisstopo). It supports typical planimetric and altimetric reference frame changes for Switzerland. For more information on which reference frames are supported, please see the documentation.  

 

Additional Resources

[Blog] Heights in Coordinate Systems
[Article] Creating Vertical Adjustment Grid files for use with FME