Attitude Coverage Grid

In contrast to the grid in Coverage, the points and regions on the Attitude Coverage grid refer not to geographic locations but to pointing directions. Conceptually, the points and regions can be seen as projected on an imaginary sphere centered on the object. This is represented visually in the 3D Graphics window through an Attitude Sphere. Regions are defined by closed boundaries that contain points. Accessibility to an asset via a region is computed on the basis of accessibility to the asset via points within that region.

You can define an Attitude Coverage grid for an Attitude Coverage object in STK. Highlight any Attitude Coverage object and right-click to open its Properties. Under Basic, select Grid and use the Grid property panels described below to define the extent of a coverage grid. This includes defining the boundaries of the coverage area and setting the resolution of the grid points used to fill the bounded area.

Grid area of interest

To define a coverage area on the attitude sphere, you must first choose an area type. From the Type menu, choose one of the following:

Option	Description
Global	This choice tells STK to create a grid that covers the entire attitude sphere. It may take a long time for STK to calculate data due to the number of points computed when covering the whole sphere.
Latitude Bounds	This choice tells STK to create a grid between user-specified minimum and maximum horizontal boundaries, labeled Min. Latitude and Max. Latitude. When the sphere is centered on an Earth-based object, you can use this option to exclude downward directions from consideration or to impose a minimum and maximum elevation angle constraint.
Latitude Line	This choice tells STK to create a set of points along a single latitude line on the sphere. This option is useful when the coverage is only expected to vary with longitude. It greatly reduces the number of points for STK to calculate and therefore provides resulting data much more quickly. Enter values for Start Longitude, Stop Longitude, and the Latitude of interest.
Longitude Line	This choice tells STK to create a set of points along a single meridian on the sphere. This option is useful when the coverage is only expected to vary with latitude. It greatly reduces the number of points for STK to calculate and therefore provides resulting data much more quickly. Enter values for Min Latitude, Max Latitude, and the Longitude of interest.

Point granularity

Control the resolution of your coverage analysis by specifying the angular distance between grid points in terms of degrees of latitude and longitude on the sphere. A finer resolution leads to more accurate results but increases computation time. STK stretches grid points in longitude at high and low latitudes in an attempt to preserve the angular area associated with the grid point.

Grid reference axes

Click Select... and choose a reference frame for the Attitude Coverage. This need not be the same as the reference frame that you use for the Attitude Sphere.

Point locations

The default is Compute Locations Based on Granularity. This tells STK to place points within a coverage grid based on the Point Granularity value that you set. However, you can also specify each point within a grid for calculation purposes. To choose the location of specific points within the grid, select Custom Locations and click Specify... to open the Point File List window.

To add a point file to the list, click Add and then click on the blue band. When the Open window appears, select the point list (*.pnt) or shapefile (*.shp) that contains the points of interest. Both the point list and shapefile contain latitude and longitude point pairs. If you select a file that contains points lying outside of the selected area boundaries, STK discards those points from the current analysis.

Although the specification of exact point locations removes the effects of the Point Granularity value, the resolution is still used in the computation of the angular area associated with each grid point.

You can add one or more files to the list. When the list is complete, click OK to return to the Basic Grid page.

Grid constraint options

To select an object for determining access to selected assets or for calculating figures of merit, click Grid Constraint Options.... Set the following options:

Option	Description
Use Object Instance for Constraints	To assign additional access constraints to the grid points, select the Use Object Instance for Constraints box and select an Object Class. This displays all objects of that type. Select an object from the list.
Use Actual Object on the Grid Points	If you select the Use Actual Object on the Grid Points box, coverage computations will use the actual object in the scenario that you selected. If not selected, a copy is used. Using the actual object speeds up coverage computations but may result in unexpected and undesired changes to the object. Using a copy prevents such consequences but can slow down computations. If you are defining coverage using a sensor as an asset and that sensor is targeted to the grid point object, you must select Use Actual Object on the Grid Points. This will ensure that the sensor targeting is updated for each grid point. This also applies to objects attached to such targeted sensors.
Use Selected Vector	This defines the relationship between the object pointing and a grid point direction. If you select the Use Selected Vector box, the object's boresight is assumed to point along a grid point direction using the azimuth and elevation pointing method with the Rotate option. After you select the box, click Select.... The Select Vector window appears; choose a particular vector to be pointed in the grid point direction. The object's dependency on this vector then affects the object pointing direction. When STK completes the Attitude Coverage computations, it restores the original pointing of the vector. The only vectors available for selection are those defined as Fixed in Axes and using the same Reference Axes listed on the Grid Definition properties page. If the Select Vector list is empty, either launch the Vector Geometry Tool to define a Fixed in Axes vector, or change the reference axes listed on the Grid Definition properties page.

Option

Description

Use Object Instance for Constraints

To assign additional access constraints to the grid points, select the Use Object Instance for Constraints box and select an Object Class. This displays all objects of that type. Select an object from the list.

Use Actual Object on the Grid Points

If you select the Use Actual Object on the Grid Points box, coverage computations will use the actual object in the scenario that you selected. If not selected, a copy is used. Using the actual object speeds up coverage computations but may result in unexpected and undesired changes to the object. Using a copy prevents such consequences but can slow down computations.

If you are defining coverage using a sensor as an asset and that sensor is targeted to the grid point object, you must select Use Actual Object on the Grid Points. This will ensure that the sensor targeting is updated for each grid point. This also applies to objects attached to such targeted sensors.

Use Selected Vector

This defines the relationship between the object pointing and a grid point direction.

If you select the Use Selected Vector box, the object's boresight is assumed to point along a grid point direction using the azimuth and elevation pointing method with the Rotate option.

After you select the box, click Select.... The Select Vector window appears; choose a particular vector to be pointed in the grid point direction. The object's dependency on this vector then affects the object pointing direction. When STK completes the Attitude Coverage computations, it restores the original pointing of the vector.

The only vectors available for selection are those defined as Fixed in Axes and using the same Reference Axes listed on the Grid Definition properties page. If the Select Vector list is empty, either launch the Vector Geometry Tool to define a Fixed in Axes vector, or change the reference axes listed on the Grid Definition properties page.