Grid Area of Interest | Point Granularity | Grid Reference Axes | Point Locations | Grid Constraint Options

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 closed boundaries that contain points. Accessibility to an asset via region is computed on the basis of accessibility to the asset via points within that region.

Use the Grid properties 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 with grid points.

Grid Area of Interest

To define a coverage area, you must first choose an area type:

Option	Description
Global	Creates a grid that covers the entire sphere. Due to the number of points computed when covering the sphere, the time that is required to calculate data when using this option may be large.
Latitude Bounds	Creates a grid between the user-specified Minimum and Maximum Latitude boundaries. When the sphere is centered on an Earth-based object, this option can be used to exclude downward directions from consideration, or to impose a minimum and/or maximum elevation angle constraint.
Longitude Line	Creates a set of points along a single meridian. This option is useful when the coverage is only expected to vary with latitude, as it greatly reduces the number of points to be calculated and, therefore, provides resulting data much more quickly. Enter Min Latitude, Max Latitude and Longitude values.
Latitude Line	Creates a set of points along a single latitude line. This option is useful when the coverage is only expected to vary with longitude, as it greatly reduces the number of points to be calculated and, therefore, provides resulting data much more quickly. Enter Min Longitude, Max Longitude and Latitude values.

Point Granularity

To control the resolution of your coverage analysis, specify the angular distance between grid points in terms of degrees of latitude and longitude. As you might expect, a finer resolution leads to more accurate results but increases the computation time. STK stretches grid points in longitude at higher or lower 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

Points within a coverage grid are usually placed by STK based on the resolution value that you set. However, you can also set each point within a grid for calculation purposes. To identify the location of specific points within the grid, select Custom Locations, and click Specify....

To add a file to the Point File list, click Add, and then double-click the new entry in the list. 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, those points are discarded from the current analysis.

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

One or more files can be added to the list. When the list is complete, click OK to return to the Basic Grid page.

Grid Constraint Options

To specify an object whose properties can be used in determining access to the selected assets, or in figure of merit calculations, click Grid Constraint Options....