Initial Geolocation

You can add an Initial Geolocation object to a facility or surface vehicle by highlighting it in the Object Browser and choosing one of these options:

Click the down arrow next to the Facility icon () or Surface Vehicle icon () in the toolbar, select Initial Geolocation () from the object catalog dialog box, and click Insert.
In the Insert menu, select New, and then select Initial Geolocation () from the Insert Default Object catalog dialog box and click Insert.

Initial Geolocation is the process of estimating the location of a ground-based object using measurements produced between an emitter at the ground-based object and a set of satellites. The accuracy of the estimation depends on the quality of the measurements, the geolocation method used, and the satellite configuration. ODTK only supports some measurements and satellite combinations for the Initial Geolocation process, based on the MeasurementType and GeolocationMethod<variable> properties. The MeasurementType property determines the measurement type used for the Initial Geolocation process. The GeolocationMethod<variable> property determines the satellite configuration that ODTK uses to conduct the geolocation process. The selected MeasurementType determines its suffix (<variable>) and internal properties.

To run the Initial Geolocation process, highlight the Initial Geolocation object in the Object Browser and either click Run () in the toolbar or click the Initial Geolocation menu and select Run ().

Common properties

To see an Initial Geolocation object's properties, double-click it in the Object Browser or right-click it and select Properties. All Initial Geolocation objects share the following common properties:

Initial Geolocation Properties
Property	Description
MeasurementType	This is a read-only quantity that depends on the parent object: For a facility: SB TDOA For a surface vehicle: SB TDOA SBE Measurements of this type will be available for use with the initial geolocation process. Although a surface vehicle is on a central body, ODTK still considers it a "space-based" asset for measurement classification purposes. So for an SB TDOA measurement with the emitter on a surface vehicle, ODTK considers this an SB TDOA SBE measurement.
GeolocationMethod<variable>	This contains the measurement-specific configuration properties. The MeasurementType determines the <variable> part of the property name. Thus, if MeasurementType = SB TDOA, then GeolocationMethodSBTDOA is available.
Output	This contains solution data generated after running the Initial Geolocation process. Configuring the Initial Geolocation and running the Initial Geolocation process will update the contents of the child properties.
SolutionList	This is a list of all possible solutions generated from the last run of the Initial Geolocation process. To select a solution to transfer to the parent object: Click the "click to display" text next to SolutionList and select the name of a solution from this list . Click Select. Close the list. Apply all changes to the geolocation object. Click the “Transfer to Facility” icon () on the toolbar or in the Initial Geolocation menu. This icon applies to both Facility and Surface Vehicle objects. ODTK will record, in the Message Viewer, any errors that occur from the solution transfer .

GeolocationMethodSBTDOA properties

Initial Geolocation with SB TDOA or SB TDOA SBE measurements represents an estimation of the object location using the TDOA of an object's emitted signal that is captured by a set of satellites.

Selected satellites must not be coplanar, but they can be of any orbit regime. In this type of estimate, each TDOA measurement generates a hyperboloid along which the emitter is expected to be located. Some methods further restrict this hyperboloid with an earth-surface constraint. With two or more TDOA measurements, the intersections of the hyperboloids dictate possible solutions for the emitter location. Larger variations between the orbit geometry of each TDOA pair tend to lead to less error in solution estimates.

The following properties are available for GeolocationMethodSBTDOA:

GeolocationMethodSBTDOA Properties
Property	Description
GeolocationMethodSBTDOA	Select a method for calculating the Initial Geolocation. This selection determines the algorithm behind the geolocation process, how many satellites the algorithm uses, and how many distinct emitted signals the algorithm needs. The options are: Instant3Collector – Three satellites collect a single emitted signal and produce SB TDOA or SB TDOA SBE measurements with the data. The algorithm applies an earth-surface constraint to limit the solution space. Instant4Collector – Four satellites collect a single emitted signal and produce SB TDOA or SB TDOA SBE measurements with the data.
Emitter	Select an emitter. ODTK will only display — in the SelectedMeasurements property — SB TDOA or SB TDOA SBE measurements generated with this emitter .
MeasurementSampleSize	Use this to limit the number of points displayed when you select the measurement set (see below). This value is 300 by default. So if you use the default value, no matter how many measurements are available, you will only see the first 300 measurements in the list.
SelectedCollectors	Click where indicated to select satellites that ODTK will use in the Initial Geolocation process. You must select the exact number of satellites required by the geolocation method selected. Instant3Collector – three satellites Instant4Collector – four satellites
SelectedMeasurements	Click where indicated to select points to define your measurement set. The measurements displayed are SB TDOA or SB TDOA SBE measurements that occur between the emitter and satellites from the SelectedCollectors list. This list contains four columns: First column – Time in seconds relative to the first measurement in the list Second column – Full time string for the first measurement; measurements are time-tagged according to the receive time at the first satellite Third column – The ID of the tracking instrument on the first satellite Fourth column – Tracking ID of the second satellite The exact rules for selected measurements depend on the geolocation method selected. Instant3Collector – You must select exactly two measurements, and these must use each of the three satellites. All measurements must originate from the same signal emission. Instant4Collector – You must select exactly three measurements, and these must use each of the four satellites. All measurements must originate from the same signal emission.