So we have just added RS2 to our Emlid assets and the testing has begun. So far, so good. Big reason for adding the RS2 was that the RS+ was logging in WGS84 while the NTRIP corrections were in NAD83/17N, and then there was the height conversions to elevation, using HTv2.0 (2010).
So, with the RS2, I can now apply NAD83/17N (EPSG:26917) but when it comes to vertical corrections, I have the choices suitable choices of CGVD2013, CGVD2013a, and CGVD28…and many more that don’t fit my location and requirements. However, there is no HT2-1997, HT2-2002 or HT2-2010. I point this out because its my understanding they are all related.
Even though the Canadian Geodetic Vertical Datum of 2013 (CGVD2013) has been the official vertical datum of Canada since 2013, there are still many users in survey, engineering, construction and mining sectors using the HT2 hybrid geoid model to convert the heights (ellipsoidal heights) to elevation (orthometric heights) during a GNSS survey. The current version of the HT2 hybrid geoid model is at epoch 1997.0. This means that it must be used in a GNSS survey when the geometrical coordinates (Latitude, Longitude, Height) are at Epoch 1997.0 of NAD83 (CSRS).
Most of the provincial and federal geodetic agencies updated their reference epochs to either 2002.0 or 2010.0; therefore, in order to use the HT2 hybrid geoid model when conducting surveys using GNSS, new versions of the model in epoch 2002 and 2010 must be used. In Ontario Canada the adopted NAD83 (CSRS) epochs is 2010.
Depending on the Epoch of the NAD83 (CSRS), the relevant geoid model must be used. For example, the users of the Can-Net system in Ontario must use the HTv2.0 (2010) model because the reference epoch for Can-Net in Ontario is 2010.
Canadian Geodetic Survey (CGS) recently released two new versions of the HT2 model, HTv2.0 (2002) and HTv2.0 (2010). The name of the previous model was changed to HTv2.0 (1997). The new Epochs of the HT2 model are built directly from HTv2.0 (1997) by simply adding a 5 and 13-year vertical velocity correction to the hybrid geoid heights. The corrections range from -0.087 m to 0.379 m.
The Canadian Geodetic Survey highly recommends the use of CGVD2013 when conducting surveys using GNSS. The development of the new epochs for the HT2 geoid model does not mean that CGS will resume the maintenance of the first-order benchmarks in CGVD28 by levelling or GNSS technique. The new epochs of the HT2 geoid model are temporary products until CGVD2013 is well established within the geomatics community.
The questions resulting from the long and boring back story are;
- Can you import datums if you have downloaded the HT2-1997,2002 and 2010 models?
- While I’m glad to see the CGVD2013 and CGVD2013a models available, why not add the HTv2 models if they are still in use on some projects and until the transition is fully done?
Interested in hearing others thoughts.