The IOD object is represented in the Browser and in the ODTK toolbar by the icon. Click the IOD object in the Browser to expose its properties, and select HerrickGibbs, GoodingAnglesOnly or GNSSNavSolution as the Method.
The HerrickGibbs IOD method uses three sets of range plus direction measurements to generate an initial orbit solution for a geocentric spacecraft. The directional information can be in the form of azimuth/elevation angles or direction cosines. The following properties are available for the HerrickGibbs method:
HerrickGibbs Properties  

Property  Description 
SelectedFacility  Select the desired tracking station from the dropdown list. If the IOD object is created after tracking data has been loaded in the scenario object, then by default the selected Facility will be the first Facility with tracking data for the associated satellite. 
MeasurementPass  The HerrickGibbs IOD method allows you to select three (3)
observations from the tracking data. You are offered a list of
measurements to select from, which may span several orbit
revolutions or several passes of tracking data. You are responsible
for choosing a span of data that is consistent with the Herrick
Gibbs algorithm. The Herrick Gibbs algorithm is valid for a
selection that spans substantially less than one orbit period, and
is typically applied to three measurements from the same tracking
pass. To assist you in selecting data, time is presented in two ways, as seconds since the first point in the file and as a full datetime string, together with the range and elevation for each observation. 
MeasurementSampleSize  Allows you to set a limit on the number of points displayed when you select the measurement set (see below). This value is 300 by default, so that no matter how many measurements are in the first pass, you will see only the first 300 points. 
MinimumElevation  Allows you to exclude measurements when the satellite is less than the specified angular distance above the horizon. 
SelectedMeasurements  Click where indicated to display a List window, which provides
a means of selecting points to define your measurement set. The
list contains 3 columns:
Note: A facility must be selected prior to selecting measurements. 
Output  Set the OrbitState field to Cartesian or Keplerian. When IOD is run, readonly fields display the orbit state and the satellite's epoch (based on that of the middle point in the measurement set). 
Output.DataArchive  Set the "OutputStateHistory" to true to output an .iodrun state history file. Name the run file with the "Filename" property. The state history will contain one record with the output IOD orbit state at the IOD epoch time. 
Note: HerrickGibbs IOD uses satellite transponder bias as well as the facility measurement biases in its calculation process. The ODTK HerrickGibbs IOD accepts standard range (eMTRange) and laser normalpoint range (eMTNPRange) as a valid range type. Range plus directional measurements must be loaded as part of the same observation set in the tracking data loader to be recognized as usable by the HerrickGibbs algorithm.
The GoodingAnglesOnly IOD method uses three sets of anglesonly measurements to determine the orbit of a geocentric spacecraft. In ODTK the angle set may be ground based azimuth and elevation, ground based RA and DEC, ground based X and Y, ground based Direction Cosines, ground based phased array Face Angles, or space based RA and DEC. Measurements may come from a single or multiple tracking stations (or satellites). Measurements are not limited to a specific range in orbital arc, although white noise and twobody dynamic considerations may apply in choosing the measurement sets (see the Wright reference, below).
REFERENCE: R. H. Gooding, A New Procedure for Orbit Determination Based on Three Lines of Sight (Angles Only), Technical Report 93004, Defence Research Agency, Farnborough, Hampshire, April 1993.
REFERENCE: J. R. Wright, Implementation of Gooding's AnglesOnly IOD, Analytical Graphics, Inc.
More detailed information on the use of this method follows this table:
GoodingAnglesOnly Properties  

Property  Description 
TrackerList  List of trackers to consider. 
StartTime  Only display measurements after (and including) this time. 
StopMode  Select among:

StopTime  If StartMode = StopTime, this gives the time to stop displaying measurements. Otherwise, the attribute is hidden. 
TimeSpan  If StartMode = TimeSpan, this gives time duration past the StartTime to display measurements. Otherwise, the attribute is hidden. 
MeasurementSampleSize  Allows you to set a limit on the number of points displayed when you select the measurement set. 
MinimumElevation  Allows you to exclude measurements when the satellite is less than the specified angular distance above the horizon. 
SelectedMeasurements  Click where indicated to display a List window, which provides
a means of selecting points to define your measurement set. The
list contains 5 columns:

HalfRevEstimate  Estimate of the Number of Half Revs between the first and last
(third) observation set. Half revs are considered in a "true
anomaly" sense, not orbit period. HalfRev input is rounded down,
i.e. 0 to 1/2 rev is input as 0, 1/2 to 1 rev is input as 1, etc.
NOTE: This is an important parameter to get correct; if it is incorrect it is likely that no good orbit solution will be found. 
LambertIndicator  Identifies which Lambert solution to use in the NewtonRaphson iteration. Set to 0 to use the first Lambert solution, 1 to use the second Lambert solution (this follows Gooding's convention). When the HalfRevEstimate (above)is 0 or 1, then there is only 1 Lambert solution and the LambertIndicator is set to 0 and greyed out. When the HalfRevEstimate is greater than 1, then there are exactly two Lambert solutions (or there are none), and the LambertIndicator may bet set to 0 or 1. 
Range1Estimate  Estimate of the trackertotarget range at the time of the first observation set. In most cases this does not have to be very accurate (the default of 5 Re will work for LEO, HEO and GEO), but in some cases an accurate range estimate is needed for the solution to converge. 
Range3Estimate  Estimate of the trackertotarget range at time of the third observation set. 
MaxIterations  Maximum number of iterations. 
ConvergenceValue  The solution vector convergence criterion. The default of 10^{12} is Gooding's recommendation. 
HalleyNewtonLimit  Halley/NewtonRaphson control parameter. 0 for pure NewtonRaphson, 0.5 for Halley, 1.0 for modified NewtonRaphson. Nominally the Halley method is used, but Gooding found that when two or more solutions are close together relative to the starting point, then modified NewtonRaphson works better. 
NumericPartialEpsilon  Standard partial derivative "increment factor" 
T12  Readonly parameter giving time between the first and second observation set. Currently this is not updated after the SelectedMeasurements field is updated, but only after the IOD method is run. 
T13  Readonly parameter giving time between the first and third observation set. Currently this is not updated after the SelectedMeasurements field is updated, but only after the IOD method is run. 
Solutions  NumberOfSolutions  Readonly parameter giving the number of solutions returned by the GoodingAnglesOnly algorithm. 
Solutions  UseSolution  For multiple solution cases, determines which solution is displayed in the Output  OrbitState field. The user can cycle through the different solutions by resetting this parameter and rerunning the IOD method. 
Output  OrbitState  Set the OrbitState field to Cartesian or Keplerian. When IOD is run, readonly fields display the orbit state and the satellite's epoch. The epoch time is the time of the second observation set. The solution displayed (for multiple solution cases) is controlled by the "UseSolution" parameter. 
Output.DataArchive  Set the "OutputStateHistory" to true to output an .iodrun state history file. Name the run file with the "Filename" property. The state history will contain one record with the output IOD orbit state at the IOD epoch time. 
EllipticSolutionsOnly  When set to true only elliptic solutions are considered. When set to false both elliptic and hyperbolic solutions are considered. 
Running the method may result in 0 solutions, 1 solution or multiple solutions:
The IOD solution uses either GNSS Pseudorange observations or CA/DF Nav Sol observations as inputs. The method of the solution can be broken into two steps. When using pseudorange measurements, we first compute user S/C Position and Clock Phase estimates using an analytical NAV solution algorithm developed by Yang and Chen for several points around the time of interest. When the Nav Sol measurements are used, the clock phase is not calculated and the position estimates are taken directly from the measurements. The second step, regardless of measurement type, is to use LaGrange interpolation on the position estimates to compute the velocity estimates.
REFERENCE: Ming Yang and KuoHwa Chen, "Performance Assessment of a Noniterative Algorithm for GNSS Absolute Positioning", Proc. Nat'l Sci. Counc. ROC(A) Vol. 25, No. 2, 2001, pp. 102106.
When using this method in conjunction with GNSS Pseudorange measurements, it is necessary to have measurements from 4 satellites at considered measurement times, including at the solution epoch.
The following options are available for the GNSSNavSolution method:
GNSSNavSolution Properties  

Property  Description 
SelectedReceiver  Open the dropdown list to select a GNSSReceiver object attached to the same satellite as the current IOD object. 
SolutionEpoch  The epoch time of interest. This time must be within one hour of an actual measurements time. The actual solution time is reset to match an observation time closest to the requested SolutionEpoch. 
GNSSObsType 
The measurement type to be used. Choices can be:

LaGrangeOrder  The interpolation order to use for velocity computation. 
Output  OrbitState  Set the OrbitState field to Cartesian or Keplerian. When IOD is run, readonly fields display the orbit state and the satellite's epoch. 
Output  ClockPhaseError  The clock phase error is the difference between the GNSS receiver clock and the GNSS master clock. The clock phase is one of the elements of a GNSS navigation solution. 
Output.DataArchive  Set the "OutputStateHistory" to true to output an .iodrun state history file. Name the run file with the "Filename" property. The state history will contain one record with the output IOD orbit state at the IOD epoch time. 
For practice in setting up and using the IOD object, see Exercise 2.1 in Getting Started with ODTK.
ODTK 6.5