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I have latitudes, longitudes and ellipsoidal heights derived from GPS readings, referenced to the ITRF08 system with vertical datum (CGVD2013) - http://webapp.geod.nrcan.gc.ca/geod/hmod/hmod.php

How can I convert the data to another reference system and another vertical datum?

I might need to convert the lat lon height data at every sampling interval in a RINEX file to another reference system and datum. The amount of data may be large and hence I doubt a web-based conversion platform would be suitable.

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  • Look into these free tools PostGIS, GEOS, Proj4 and GDAL. Or (not free) Safe FME.
    – Martin F
    Apr 17 '15 at 15:40
  • Surely a duplicate of ...?
    – Martin F
    Apr 17 '15 at 16:07
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You can use PostGIS for this. To perform vertical datum transformations, you'll have to add your own SRID to the spatial_ref_sys table with the appropriate WKT and proj4 parameters.

For example, if you query the spatial_ref_sys table for NAD83(CSRS) UTM12 (EPSG:2956),

select proj4text from spatial_ref_sys where srid=2956;

you get:

+proj=utm +zone=12 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 

Modify this with the geoidgrids parameter,

+proj=utm +zone=12 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
    +geoidgrids=CGG2013n83.gtx

When you transform your data, you can temporarily assign the new SRID for transformation purposes, then convert it back:

select st_setsrid(st_transform(st_setsrid(geom, xxxx), yyyy), 2596) [etc.]

where xxxx and yyyy are your 3D SRIDs.

Note: CGG2013n83.gtx isn't available from NRCAN. They provide it as a .byn file. I converted it myself using a utility I wrote for that purpose.

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