Antenna Models

The simple model, and generic profile, for the advanced method are identical. They assume that the L1 and L2 phase centers are coincident and have no offsets from the antenna height measurement. For each antenna profile, the following information can be edited:

•The antenna model

•The manufacturer

•The horizontal distance from the phase centre to the edge of the ground plane

•The L1 and L2 phase offsets from the origin

•The location of the origin on the antenna

To measure to the ground plane, enter a slant distance instead of a vertical antenna height. GrafNav uses Pythagorean Theorem to calculate the antenna height using the slant distance and the horizontal distance in the antenna profile. However, this requires the creation of a profile, as those loaded with the software are obtained from the NGS (National Geodetic Survey), who do not often measure the ground plane radius. See Section 2.4.7, on Page 57 for information about antenna heights for static sessions.

The antenna origin must be moved to antenna ground plane. Refer to http:// www.novatel.com/products/ waypoint_faqs.htm for more information.

2.3.7Add Remote Files

When starting a new project, the program needs the data collected from the remote station.

This antenna height applies primarily to kinematic trajectories and features, such as stations or events, and static sessions override it.

If an antenna height is not entered, the program assumes that the height was zero and calculates heights based on this information. If an STA (station) file exists and a station mark is present in that file, the last antenna height shows up by default.

See Section 2.3.6, on Page 36 for information regarding antenna height models.

How to add a remote file

1.Select File | Add Remote File after giving the new project a name and adding the master GPB file(s). From the list of available GPB files, choose the file collected at the remote station.

2.When prompted, enter the remote station antenna height.

How to change the remote antenna height on specific static sessions

1.Select View | Objects | KAR/Static.

2.Click Edit for each static session.

How to specify alternate ephemeris files

1.Go to File | Alternate Ephemeris Files. The program displays a list of ephemeris files (EPP), precise ephemeris files (SP3/ SP3c), IONEX files (yyI), and clock files (CLK).

2.Select the appropriate EPP file.

How to load ephemerides from different stations

1.Select Tools | Download Service Data.

2.Download data from the nearest station for the day of interest.

3.For precise ephemeris, select the Options tab and enable precise ephemeris download.

2.3.8Alternate Precise / Correction Files

Broadcast Ephemeris

The ephemeris file contains trajectory information used to reconstruct the orbit of each satellite. This data is necessary for GPS positioning.

Generally, the GNSS receiver includes broadcast ephemeris data with its raw data files. Either the decoder or the logging software converts these files into EPP format. You should monitor data logging to ensure that enough ephemerides are being saved. Ephemeris information is usually updated every 1- 2 hours. Receivers will also output ephemerides at startup or as satellites rise into view.

GrafNav overcomes missing ephemeris data by searching all EPP files associated with the master, or remote, files in the project. If none of the EPP files in the project contain the necessary ephemeris, you can obtain them from a specified alternate source, for instance, CORS or IGS. See the shaded box for steps on how to specify alternate ephemeris files.

Ephemerides from different stations, or precise ephemerides that span over a day, can be added to the list to be included with the processing. See the shaded box for steps on how to load ephemerides from different stations.

Precise Ephemerides

Precise ephemerides are satellite trajectories computed post-mission. They are much more accurate than broadcast ephemerides but for differential processing, this accuracy improvement is not noticeable and is generally lost in the noise. However, for PPP processing, precise ephemerides are required.

A precise ephemeris is useful for single point processing. Geodetic services such as National Geodetic Survey (NGS) in the United States, the Geodetic Survey of Canada and some European agencies compute these orbits on a continual basis. In most cases, this data is available at a few days latency. The easiest way to download SP3 files is via Waypoint’s download program. See Chapter 7 on Page 207 for details.

Waypoint software only supports precise orbits stored in the SP3 format (most agencies use this format). Orbits which have been optimized for the United States are available free of charge from NGS via their website (www.nga.mil).

Waypoint software’s precise orbit implementation requires that a broadcast ephemeris orbit is available. Precise ephemerides cannot be used to circumvent missing broadcast orbit information. If a broadcast ephemeris is missing, consider downloading data from the nearest CORS or IGS station. See Section 2.8.12, on Page 140 for help.

IONEX and Satellite Clock Files

IONEX (Ionosphere Map Exchange files) contain information concerning the Total Electron Count (TEC) in a two-dimensional grid. For single frequency long-range differential or single point processing, the information in an IONEX file adds corrections helpful to the L1 frequency and are available through the Download Service Data utility.

Satellite clock files can also be downloaded using the Download Service Data utility. These files contain a list of biases that can assist single point positioning because the clock bias is only differenced out in differential positioning. For PPP, these files are required.

How to load a precise ephemeris file in the SP3 format

1.Go to File | Alternate Ephemeris Files. The program displays a list of ephemeris files (EPP), precise ephemeris files (SP3), IONEX files (yyI), and clock files (CLK).

2.Select the appropriate SP3 file.

How to load IONEX files and satellite clock files

1.Go to File | Alternate Ephemeris Files.The program displays a list of ephemeris files (EPP), precise ephemeris files (SP3), IONEX files (yyI), and clock files (CLK).

2.Select the appropriate yyI and/or CLK file.

View/Edit GPS option settings

Show Station Info

Displays information about the station.

Show GPB Info

Displays information about the GPB file.

Show Time Gaps

Displays information about any time gaps in the data.

View Raw GPS Data

Opens the master file in GPB Viewer.

View Ephemeris File

Opens the EPP file in the internal viewer.

View Station File

Opens the STA file in the internal viewer.

Insert Static/Kinematic Markers

Opens up the menu to insert static/kinematic markers in the file.

Resample/Fill Gaps using the following options

•File Interval – fills all gaps by resampling using the data interval.

•Processing Interval – fills gaps and lowers or raises the data rate in accordance with the specified processing interval.

•Remote File Times – produces a GPB file with epoch times that match the remote file. Any data gap present in the remote file is also present in the new master GPB file. This method of resampling removes unneeded data logged before, and after, the observation time period at the remote. It allows resampling of GPB files that do not sample at a constant rate, examples of these files include SiRF, GSU and I/II.

Resampling can cause additional errors. If you are resampling intervals of 5 seconds or less, the error is negligible for kinematic processing but for 30 second data, this error is 1-2 cm and hampers integer ambiguity resolution. Resampling should not be performed for static processing.

Disable

Disables the selected master station from being used for processing.

Remove

Removes the master file completely from the project.

Plot L1 Locktime

Launches the L1 Satellite Lock/Elevation plot.

Plot L2 Locktime

Launches the L2 Satellite Lock/Elevation plot.

2.3.9 Show Master Files

Object

This command brings up the Object menu for the base stations, where the following features are available:

View

Brings up the Object Info message box for the selected base station.

Edit

Allows you to edit the name, coordinates, and antenna height of the selected base station.

View/Edit GPS

Displays a list of actions that are listed in the shaded box.

Disable

Disables the selected master station from being used for processing.

Remove

Removes the master file from the project.

Add to Favourites

This adds the object with solution to the list of Favourites. See Section 2.8.10, on Page 135 for more details.