semread

Reading data from the SEM almanac file.

Library

EngeeNavigation

Syntax

Function call

data,title = semread(filename) — reads data from the almanac file for the System Effectiveness Model (SEM) for the date specified in the file filename, and returns the parameters of each corresponding satellite as tabular data data, as well as the title of the almanac title.

data,title = semread(filename,GPSWeekEpoch=refdate) — sets the starting date from which the week number in the Global Positioning System (GPS) is counted in the SEM almanac file.

Arguments

Input arguments

# filename is the name of the SEM almanac file

+ line

Details

The name of the SEM almanac file for reading data, set as a string. The file name can contain an absolute path, a relative path, or no path at all. The file name may also include an extension.

Типы данных

String

# GPSWeekEpoch — countdown date

+ "06-Jan-1980" | "21-Aug-1999" | "06-Apr-2019"

Details

The reference date set as a format string DateTime, from which the GPS number of the week is calculated in the SEM almanac file.

These dates are repeated every 1024 weeks, starting on January 6, 1980 at 00:00 (UTC). The default value is the date and time string, which matches the last date of the GPS week number transfer before the current day.

Типы данных

String

Output arguments

# data — parameters of each satellite

+ tabular data

Details

The parameters of each satellite returned as tabular data, where each row corresponds to a separate record, and each column corresponds to a parameter of this record. For more information on determining the parameters of the SEM almanac, see table 40-II of the ICD-GPS-240D standard [2].

Parameters Data type Description

Parameters	Data type	Description
`Time`	`DateTime`	The time according to the GPS clock, calculated using the parameters `GPSWeekNumber` and `GPSTimeOfApplicability`
`GPSWeekNumber`	`Float64`	GPS week number. This is a continuous number, not `mod(1024)`
`GPSTimeOfApplicability`	`Float64`	The number of seconds since the beginning of the GPS week
`PRNNumber`	`Float64`	The number of the satellite’s pseudorandom code
`SVN`	`Float64`	Satellite identification number
`AverageURANumber`	`Float64`	The average value of the accuracy of determining the range for the user (User Range Accuracy, URA) of the satellite
`Eccentricity`	`Float64`	The eccentricity of the orbit
`InclinationOffset`	`Float64`	Deviation of the angle of inclination from `54` degrees, in semicircles
`RateOfRightAscension`	`Float64`	Rate of change of right ascension, in semicircles per second
`SqrtOfSemiMajorAxis`	`Float64`	The square root of the semimajor axis, in m^1/2
`GeographicLongitudeOfOrbitalPlane`	`Float64`	Geographical longitude of the orbital plane at the time of the weekly epoch, in semicircles
`ArgumentOfPerigee`	`Float64`	The angle from the equator to the perigee, in semicircles
`MeanAnomaly`	`Float64`	The angular position of the satellite in orbit relative to perigee, in semicircles
`ZerothOrderClockCorrection`	`Float64`	Zero-order correction to satellite clock readings, in seconds
`FirstOrderClockCorrection`	`Float64`	First-order correction to satellite clock readings, in seconds per second
`SatelliteHealth`	`Float64`	Satellite status (serviceability) code
`SatelliteConfiguration`	`Float64`	Satellite configuration code

Time

DateTime

The time according to the GPS clock, calculated using the parameters GPSWeekNumber and GPSTimeOfApplicability

GPSWeekNumber

Float64

GPS week number. This is a continuous number, not mod(1024)

GPSTimeOfApplicability

Float64

The number of seconds since the beginning of the GPS week

PRNNumber

Float64

The number of the satellite’s pseudorandom code

SVN

Float64

Satellite identification number

AverageURANumber

Float64

The average value of the accuracy of determining the range for the user (User Range Accuracy, URA) of the satellite

Eccentricity

Float64

The eccentricity of the orbit

InclinationOffset

Float64

Deviation of the angle of inclination from 54 degrees, in semicircles

RateOfRightAscension

Float64

Rate of change of right ascension, in semicircles per second

SqrtOfSemiMajorAxis

Float64

The square root of the semimajor axis, in m^1/2

GeographicLongitudeOfOrbitalPlane

Float64

Geographical longitude of the orbital plane at the time of the weekly epoch, in semicircles

ArgumentOfPerigee

Float64

The angle from the equator to the perigee, in semicircles

MeanAnomaly

Float64

The angular position of the satellite in orbit relative to perigee, in semicircles

ZerothOrderClockCorrection

Float64

Zero-order correction to satellite clock readings, in seconds

FirstOrderClockCorrection

Float64

First-order correction to satellite clock readings, in seconds per second

SatelliteHealth

Float64

Satellite status (serviceability) code

SatelliteConfiguration

Float64

Satellite configuration code

Типы данных

DataFrame

# title — the title of the almanac

+ line

Details

The title of the almanac, returned as a string.

Типы данных

String

Recommendations

To download the SEM Almanac files from the website NAVCEN for the current date, it is necessary to specify a date two days earlier than the current one, since the moment of GPS data applicability occurs approximately 70 hours after the transmission time of the almanac dataset.

Literature

Science Applications International Corporation. NAVSTAR GPS Space Segment/Navigation User Interfaces. IS-GPS-200M. Los Angeles, CA: United States Space Force Space Systems Command, approved May 21, 2021. https://www.navcen.uscg.gov/sites/default/files/pdf/gps/IS_GPS_200M.pdf.
Science Applications International Corporation. NAVSTAR GPS Space Segment/Navigation User Interfaces. ICD-GPS-240D. Los Angeles, CA: United States Space Force Space Systems Command, approved May 21, 2021. https://www.navcen.uscg.gov/sites/default/files/pdf/gps/ICD_GPS_240D.pdf.
United States Coast Guard. GPS Almanacs, NANUs, and OPS Advisories Archives. US Coast Guard Navigation Center. Accessed May 6, 2022. https://www.navcen.uscg.gov/archives.