Geoid Models

Geoid Tools

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When is the Extract Tool Needed?

.   When using ProMark Field or MobileMapper Field (optional). The Extract tool may be used to crop a geoid to the sole area needed in your application, thus reducing the size of the geoid file you need to download to your receiver. The use of the Extract tool is optional in this case as complete geoids may be downloaded to the receiver without any risk of going low in memory.

.   When using FAST Survey (mandatory). In addition to having the capability to crop a geoid, the Extract tool may be used to convert a geoid file into a GSF file. GSF being the only geoid format supported by FAST Survey, using the Extract tool as a file converter is therefore a mandatory step before you can use a geoid in FAST Survey.

Installing the Extract Tool on your Computer

.   Click on the Extract Tool link located above. You are then prompted to save the Install_Geoids.exe file on your computer

.   Click Save File and wait until the download is complete.

.   Run Install_Geoids.exe on your computer. Follow the instructions on the screen to complete the installation. Click on the Close button once complete.

Downloading a Geoid to your Computer and Receiver

.   On the web page, choose a geoid and click on the corresponding link. You are then prompted to save the Install_<Geoid_Name>.exe or .msi file on your computer.

.   Click Save File and wait until the download is complete.

.   Run the Install_<Geoid_Name>.exe or .msi file on your computer. Follow the instructions on the screen to complete the installation.

If a receiver is currently connected to the computer via ActiveSync, instructions will also be provided to install the geoid file on the receiver as well (in \Program Files\Geoids Data\).

If no receiver is connected, the geoid (a *.geo file) is installed on the computer only (path: <Drive:>/Program Files (x86)/Common Files/Ashtech/Geoids/). Installation on the receiver will however be automatic next time you connect it to the computer.

.   After the geoid has been installed on the receiver, it is ready for use in ProMark Field and MobileMapper Field software.

NOTE: If the selected geoid is for use in FAST Survey, and/or you wish to limit the extent of the geoid before installing it on the receiver, tap "No" on the receiver screen when the automatic install procedure prompts you to install the selected geoid on the receiver.

Cropping a Geoid - Installing a Cropped Geoid

This function refers to the capability of the software to adjust the extent of a geoid file to a given rectangular area, corresponding to your working area.

.   From the computer's task bar, select Start>All Programs>Ashtech> Geoids.

.   Select File>Open. The program opens directly the folder containing all the downloaded geoids.

.   Choose one and click Open. The program provides a graphic representation of the geoid. Thin lines are superimposed so you can recognize the geographical area covered by the geoid and choose which section of the area you would like to use in your project.

.   Using the mouse, draw a rectangle around the desired section.

.   Select File>Save Selection, name the section of geoid and click Save. By default, the resulting file is also a "geo" file, saved to the same folder on the computer.

.   Copy the resulting file to the \Program Files\Geoids Data\ folder on the receiver, using Microsoft ActiveSync.

 

Preparing a Geoid for Use in FAST Survey

.   With your office computer, download the desired geoid as explained in Downloading a Geoid to your Computer and Receiver.

.   From the computer's task bar, select Start>All Programs>Ashtech> Geoids.

.   Select File>Open. The program opens directly the folder containing all the downloaded geoids.

.   Choose one and click Open.

.   Select File>Save, select "GSF File (*.gsf)"as the new file format, name the file and click Save. By default, the resulting GSF file is saved to the same folder on the computer.

.   Copy the resulting GSF file to the ...\FAST Survey\Data\ folder on the receiver, using Microsoft ActiveSync.

.   In FAST Survey, open the Localization function (Equip>Localizat..., GPS tab). Do the following:

-   Tap on the Geoid File button

-   Select the geoid file from the ...\Data\ folder.

-   Tap on the green tick button. The use of the geoid in FAST Survey is now effective.

Reminder: To reject the use of a geoid, go back to Equip>Localizat..., GPS tab, tap on the Geoid File button and then tap on the red cross button.

Updated April 28, 2020