art_000020;Importing Geoid Model in EZSurv

Importing Geoid Model in EZSurv

How to import a Geoid Model

Supported Geoid Format

· NRCan (Canada) *.byn files;

· Private Geoid Files *.geoid files.

The *.geoid format

Over the years we’ve been actively adding new formats to support geoid model from around the world. Because of the multiplication of formats using the same extension (*.txt for example), it became a hard task for the end user to select the correct format when importing its own geoid file. When you import your own private geoid, you’ll notice that we show two formats, NRCan *.byn files and the *.geoid files.

The support of NRCan’s file format wasn’t modified. The biggest change is the introduction of the *.geoid extension, a OnPOZ proprietary format. These files aren’t available from government agencies; it is a file that is provided by Effigis. So, if you need to import a private model in the system and it’s not in the *.byn format, you’ll have to contact us. Once we’ve received all the needed files, we will first analyze the compatibility with the system. If compatible, we’ll send you the model converted into the *.geoid format or if we consider it to be useful to other users, we will add it to the predefined geoid model list.

How to import

First you have to obtain your geoid file from your local geodetic agency or the Internet and copy it on your Windows powered device.

To import the model, use the Geoid Manager (found under Edit > Geoid...), select Use a geoid model (annotated 1 in the image below) and select the Private tab (2). From there, click on Import (3). If the model format is not found in the list of supported format, please refer to the section found above (called: The *.geoid format).

Geoid Model

In GNSS positioning, heights are computed with respect to a reference ellipsoid.

You must apply geoid undulation corrections if you want to reduce your GNSS heights to the mean sea level (MSL or orthometric height).

These corrections are usually computed using geoid proprietary tables provided by government agencies.

In differential positioning, (Base and a rover file), it is the relative geoid height which is important.

In Precise Point Positioning (no Base Station), it is the absolute geoid height which is important.

· If you select a geoid model, MSL heights can be fixed at the reference site using the Edit > Site dialog box;

· If you do not select a geoid model, ellipsoid heights can be fixed at the reference site using the Edit > Site dialog box.

After selecting a model, when you look at the Edit > Site window, only the MSL height (Mean Sea Level) value can now be fixed. If you prefer to fix the Ellipsoidal Height, select None in the Geoid Manager..

Article: 000020