Does vertical datum get projected? I feel a bit confused with the concept of the vertical datum and doing a projection.
[GIS] Vertical Datum and Projection
datumverticalvertical-transformation
Related Solutions
EPSG has added it as 6647.
At Esri, I have it in a development build, but it's not in ArcGIS 10.3 (hopefully 10.3.1). Here's the Esri WKT for it:
VERTCS["CGVD2013_height",VDATUM["Canadian_Geodetic_Vertical_Datum_of_2013"],PARAMETER["Vertical_Shift",0.0],PARAMETER["Direction",1.0],UNIT["Meter",1.0],AUTHORITY["EPSG",6647]]
This document on height modernization (1.36 MB) from Service New Brunswick shows differences from CGVD28 of +0.55 m in Banff to -0.64 m in Halifax. I would call those differences significant for more than high-end surveying work.
If you (as a GIS person) receive CGVD13 data, you'll want to make sure the metadata reflects that. Also, as it's now the official vertical coordinate reference system, government agencies may start requiring that vertical data use CGVD2013.
EDIT: How to incorporate the new definition
Esri removed the "Coordinate Systems" folder and its thousands of prj files at version 10.0. People used to drop in custom definitions there or move things around. If you're using a 10.0 or later version:
Keep custom prj files in a directory to which you have a folder connection. Then when choosing a coordinate system, you can use the "import" option to browse to that folder and pick a prj file.
(Tip: use "add to Favorites" context menu, which is a shortcut for copying prj files in the ArcGIS "Favorites" location, C:\Users\your_login\AppData\Roaming\ESRI\Desktop10.X\ArcMap\Coordinate Systems in Windows 7; replace Desktop10.x with your major release version (10.0 / 10.1 / etc.).)
The coordinate systems "picker" is smart enough that a vertical coordinate system prj file will not show up in ArcMap data frame properties' Coordinate System tab, but is available if you're using Define Projection Tool, or a data's property page in ArcCatalog.
(* You did get the name of someone who studies and practices geodesy correct!)
Convert from (EGM96) geoid vertical datum to (WGS84) ellipsoid vertical datum:
gdalwarp -s_srs "+proj=longlat +datum=WGS84 +no_defs +geoidgrids=egm96_15.gtx" -t_srs "+proj=longlat +datum=WGS84 +no_def" dem_in_egm96_geoid.tif dem_in_wgs84_ellipsoid.tif
You will need the gtx file containing vertical datum shifts from here: http://download.osgeo.org/proj/vdatum/egm96_15/
See this page for more info: https://proj.org/usage/transformation.html
You can test the result at a location using this site: https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html
Best Answer
No, when doing a map projection, the vertical coordinates are unaffected. If you look at the math behind a map projection (cf. Snyder's Map Projections: A Working Manual). you'll see that there's no mention of any vertical data. The only time you might see altitude or elevation mentioned is if the projection allows you to set its perspective point like vertical near-side perspective. Another projection used in Colombia takes the average local elevation into account to minimize the distortions. That doesn't affect the point elevations in the area though.
You can have 'horizontal' data in latitude-longitude, referenced to a geodetic/geographic coordinate reference system (CRS), or in planar coordinates (x-y or easting-northing), referenced to a projected CRS. The vertical coordinates could be gravity-related like orthometric or normal heights referenced to a geoid surface or leveling surface or ellipsoidal heights referenced to the underlying ellipsoid used by the GeoCRS.
A vertical CRS (AKA vertical datum) identifies what origin point or surface the 'z' coordinates are referenced to.
You can even perform horizontal datum transformations, like from NAD 1983 (1986) and NAD 1927, while still having the same gravity-related heights. Those heights are just transferred unchanged between the two 'horizontal' systems.
If the data has ellipsoidal heights, some types of horizontal datum transformations (Bursa-Wolf, Coordinate Frame, Position-Vector, Molodensky-Badekas, etc.) can convert the ellipsoidal heights between two GeoCRS.
Most datum transformations that use on-disk files (NADCON, NTv2, etc.) only convert the horizontal coordinates, but I've seen an overloaded NTv2 file that had vertical offset information in it as well. Some file-based methods do support both horizontal and vertical offsets and could perform both horizontal and vertical transformations.