How to Read the Legends
Post Assessment Products
Metric: This defines the analysis depicted in the chart. In this example, ‘Position Error Max(m),’ informs the reader the chart is representing maximum position error in meters. The PPS (Precise Positioning Service) Position Error Max Post Assessment charts on this site show the maximum navigation position error for the entire time period specified (see # 7.)
Production Date: Date and time chart was produced by the GPSOC. Time is in ZULU (aka GMT or UTC).
Almanac File: The name of the almanac used for this run. The almanac name contains the format (SEM), GPS week (406, which does not include the rollover 1024 weeks, meaning actual GPS week = 406 + 1024 = 1430.)
Satellite Outage File (SOF): The name given in Year_Julian Date_Zulu Time_Version format. This is always the most current SOF available at time of production.
Performance Assessment File (PAF): This is a date specific file that contains all the actual performance errors for the date specified. The PAF Julian date must match the date of analysis.
Outage Field: If any vehicles were removed from the constellation (set UNHEALTHY to users) they appear here. Listed by PRN number, then the start time of the outage (in ZULU).
Start Time and End Time: The period of time that the chart represents. Daily products run from 0000z-2359z. See Time Increment section of the technical notes for more description of this parameter.
Altitude: Maps do not include terrain; altitude is 0 ft HAE (Height Above Ellipsoid)
Latitude and Longitude Increment: Represents the size of each grid point for a region. See the Degree Increment section of the technical notes for a description of this parameter.
Number of Channels: The satellite selection algorithm used in calculating the position error for the run. Post Assessment products are created and posted for both All-In-View (12 Channel) receivers, as well as Best-4 receivers. See the satellite selection portion of the technical notes for more detail.
Mask Angle: Mask angle applied to product. Daily products will be for a 5 degree mask angle. See the Mask Angle section of the technical notes for a description of this parameter.
Color Legend: This portion of the legend defines the color shades that represent the information plotted in the chart. For Post Assessment products, the color bands represent errors in meters.
Prediction Products
Metric: This defines the analysis depicted in the chart. In this example, Position Dilution of Precision (PDOP) ‘PDOP Max’ tells the reader that the chart is representing maximum predicted PDOP for that region. DOP does not have a unit of measure, it is a multiplier of error. The Position Error 95th charts on this site show the 95th percentile predicted position error for the time period specified (see #7).
Production Date: Date and time that the chart was produced by the GPSOC. Time is in Zulu (aka GMT or UTC).
Almanac File: The name of the almanac used for this run. The almanac name contains the format (SEM), GPS week (405, which does not include the rollover 1024 weeks, meaning actual GPS week = 405 + 1024 = 1429.)
Satellite Outage File (SOF): The name given in Year_Julian Date_Zulu Time_Version format. This is always the most current SOF available at time of production.
Prediction Support File (PSF): This is a date specific file that provides an estimate for the standard of deviation of GPS satellite signal in space performance. It is used in the 95% Prediction Error products.
Outage Field: If any vehicles were removed from the constellation (set UNHEALTHY to users) they appear here. Listed by PRN number, then the start time of the outage (in Zulu).
Start Time and End Time: The period of time that the chart represents. Daily products run from 0000z-2359z. See Time Increment section of the technical notes for more description of this parameter.
Altitude: Maps do not include terrain; altitude is 0 ft HAE (Height Above Ellipsoid)
Latitude and Longitude Increment: Represents the size of each grid point for a region. See the Degree Increment section of the the technical notes for a description of this parameter.
Number of Channels: The satellite selection algorithm used in calculating the DOP and predicted error for the run. Predictive products (DOP and 95% Prediction) are created for Best-4 satellite selection. See the satellite selection portion of the technical notes for more detail.
Mask Angle: Mask angle applied to product. Daily products will be for a 5 degree mask angle. See the Mask Angle section of the technical notes for a description of this parameter.
Color Legend: This portion of the legend defines the color shades that represent the information plotted in the chart. For DOP products, the color bands represent the unitless measure of DOP. The 95% Prediction products represent predicted position error in meters.
How to Read the Charts
The following graphic depicts the different areas on a typical performance chart. See the associated numbers in the legend for each part of the text description.
The following figure shows the intermediate PDOP values for the entire 24 period for each highlighted Grid Point. The maximum values attained during the day determine what color the grid segment will be. It is possible that some areas within the specified grid segment size may have higher PDOP values than that given at one single point within the segment.
