Open up Terrascan and Read Points. It’s important to only open every 100th point for processing time.

The next step is to export a lattice model. Grid spacing of 500m is acceptable because the geoid model has km long arcs.

Filling gaps will prevent gaps in your TIN. Three decimal places will give you mm level precision.

To transform the data you must download a tool from NRCAN http://webapp.geod.nrcan.gc.ca/geod/tools-outils/applications.php?locale=en called GPS-H. It requires registration. Alternatively you could use blue marble. Select your Geoid Model and change to the correct Projection. For input select Edit.

Once this file is created you can import it into MicroStation and perform your transformation but first…

To calculate the orthometric height the geoidal height is subtracted from the ellipsoidal height

Orthometric = ellipsoidal height – geoidal height.

Microstation uses the equation

Orthometric = ellipsoidal height + geoidal height.

This means that you must first massage your data in excel and change the signs on your geoidal heights. Don’t forget to save this file as *.xyz space delimited as you will need it in microstation. I saved as a *.csv then opened it in a word editor and replaced the commas with spaces. I then saved the file again and changed the extension to *.xyz

In order to not overwrite your original blocks, you should create a new folder called Blocks_Ortho in windows explorer and move a copy of your blocks to this folder. Tell your project to reference this folder instead of the original folder.

 

 

 

 

 

 

 

 

SAVE YOUR PROJECT!

The next step is to apply your geoid adjustments

 Hit OK and selected your Geoid translation file

This will translate your file and output it to whatever name you choose.