Velocity Deviation (Batch QC Tab Parameters)

Use the Velocity Deviation tab option to calculate the speed of airborne data collection and to carry out quality control on the calculated aircraft velocity.

Velocity Deviation tab options

Velocity channel	Select the channel to store the calculated speed. Defaults to "Velocity". If the velocity channel does not exist, it will be generated and calculated as _Distance/dt in units of Km/hr. If the "_Distance" channel does not exist, it will be generated and calculated from the coordinate (X & Y) channels. See the Application Notes below for details on Velocity channel calculation. Script Parameter: QCVELOCITY.CHAN
Time channel	Select the time channel (in decimal hours). Pre-populated if a "Time" channel exists in the current database. Script Parameter: QCVELOCITY.TIME
Nominal velocity	Enter a nominal velocity (Km/hr) against which the "maximum" and "allowed" deviation options are applied. Script Parameter: QCVELOCITY.NOMINAL
Maximum deviation	Specify the maximum deviation from the nominal velocity. Script Parameter: QCVELOCITY.MAXDEV
Allowed deviation	Specify the deviation tolerance from the nominal velocity. Script Parameter: QCVELOCITY.ALLDEV
Over a distance of	Enter the distance over which the velocity deviation tests are carried out. Script Parameter: QCVELOCITY.DIST

Application Notes

The GX assumes that the current database is the one containing actual survey data. This database is called the survey database.

Velocity Channel Calculation

The X & Y channels units are used to convert the output velocity to km/hr. Note that the _Distance channel is always re-calculated even if the velocity channel already exists. The velocity is calculated at a given row using the values before and after, and the final values are interpolated and extrapolated ("nearest" at the ends) to fill in dummies.

If an existing velocity channel is selected, all the input values are assumed to be in the same units. The km/hr units are only enforced if the velocity channel is new (and calculated using the X & Y and _Distance channels); then the input deviation values are also assumed to be in km/hr.

Quality Control Specifications and Indicators

The GX creates a flag (mask) channel, called Flag_Velocity, which contains numbers from -3 to +3 inclusive to indicate the results of the quality control test(s) and how the actual velocity values deviate from the ideal velocity.

You can apply one or both of the specification tests. To disable a test, leave the field empty.

Indicators Definition

Flag_ Velocity	Description
0	Velocity = Nominal velocity +/- Maximum deviation. Velocity passes the test(s).
+1	Velocity > Nominal velocity + Maximum deviation but Velocity < Nominal velocity + Allowed deviation over specified range
-1	Velocity < Nominal velocity - Maximum deviation but Velocity > Nominal velocity - Allowed deviation over specified range
+2	Velocity > Nominal velocity + Maximum deviation but Velocity < Nominal velocity + Allowed deviation exceeding specified range
-2	Velocity < Nominal velocity - Maximum deviation but Velocity > Nominal velocity - Allowed deviation exceeding specified range
±3	Velocity > else. Velocity fails the test(s).

You can refer to the velocity test when you encounter data outside the acceptable threshold in other tests and identify if the poor quality is due to variations in the speed of the data collection. Based on how the data is collected, the reported velocity at each measurement can be a very good indicator of poor performance during data acquisition.

Plotting the Results

The results are plotted on the map using a single colour: purple. The symbols for all the flagged locations (Flag_Velocity !=0) are plotted in ground units to the left of the line path with an offset of 0.7mm.

If you would like to illustrate the type of failure on the map, generate a symbol plot of the Flag_Velocity channel using any one of the GXs: Colour Range Symbols, Proportional Size, and Colour Range.