Access Geometry¶
Access geometry determines whether two mission endpoints have a valid geometric relationship over time.
This is the basis for Link Analysis, Coverage Analysis, and any workflow that depends on visibility or contact windows.
Endpoints¶
An endpoint is an abstract geometric participant in an access computation.
Examples:
- Spacecraft.
- Ground facility.
- Sensor.
- Antenna.
- Static point.
- Mounted asset.
Endpoints may provide:
- Position.
- Velocity.
- Local surface normal.
- Attitude or local axes.
- Field-of-view capability.
- Constraints.
Line of Sight¶
Line of sight determines whether the segment between two endpoints is obstructed.
For ground-space access, this often reduces to a horizon or elevation test.
For space-space access, Earth occultation is evaluated by checking whether the segment between two positions intersects the Earth.
Field of View¶
Some endpoints expose field-of-view constraints.
Field-of-view checks can be:
- Conical.
- Rectangular.
- Sensor-specific.
- Antenna-specific.
Field-of-view masks are applied in addition to line of sight.
Constraints¶
Constraints provide additional filtering conditions.
They may come from:
- The endpoint asset.
- The endpoint host.
- A mounted sensor or antenna.
Examples include:
- Minimum elevation.
- Solar beta angle.
- Angular restrictions.
- Illumination constraints.
Access Masks and Intervals¶
The access engine evaluates a boolean mask over a sampled timeline.
That mask is then converted into intervals:
False False True True True False
|-----------|
interval
Boundary refinement can improve interval start and end times beyond the coarse time step.
Accuracy Considerations¶
Access accuracy depends on:
- Timeline step.
- Propagation fidelity.
- Endpoint interpolation quality.
- Field-of-view model correctness.
- Constraint implementation.
- Boundary refinement settings.
Short events may require smaller time steps or dedicated hidden-event detection.