Metadata-Version: 2.1
Name: satvis
Version: 0.1.1
Summary: Satellite LOS visibility calculator
Author-email: Dylan Penn <dylanrpenn@vt.edu>
License: MIT License
        
        Copyright (c) 2022 Dylan R. Penn
        
        Permission is hereby granted, free of charge, to any person obtaining a copy
        of this software and associated documentation files (the "Software"), to deal
        in the Software without restriction, including without limitation the rights
        to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
        copies of the Software, and to permit persons to whom the Software is
        furnished to do so, subject to the following conditions:
        
        The above copyright notice and this permission notice shall be included in all
        copies or substantial portions of the Software.
        
        THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
        IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
        FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
        AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
        LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
        OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
        SOFTWARE.
Project-URL: Homepage, https://github.com/dylan906/satvis
Classifier: Programming Language :: Python :: 2
Classifier: License :: OSI Approved :: MIT License
Classifier: Operating System :: OS Independent
Requires-Python: >=2.8.5
Description-Content-Type: text/markdown
Provides-Extra: dev
License-File: LICENSE

# **satvis**: A satellite visibility calculator.
## Description
*satvis* is a small library of functions used to calculate line-of-sight (LOS) visibility between spacecraft and plot access windows. The core functions that the library is based on are implementations of algorithms developed by J. A. Lawton and Salvatore Alfano et. al. Visibility windows are represented as `IntervalTree`s. Access windows are plotted using matplotlib.

## Install
```
pip install satvis
```

## Examples
### Example 1

To calculate the visibility between two Earth-centered-inertial (ECI) points:
```python
earth_radius = 6378 # km
extra_height = 0 # km
r1 = array([[earth_radius + 400, 0, 0]]).transpose() # position of object 1
r2 = array([[earth_radius, 0, 0]]).transpose() # position of object 2

[vis, phi, a1, a2] = visibilityFunc(r1, r2, earth_radius, extra_height)
print(vis)
print(phi)
print(a1)
print(a2)

# Prints:
# 0.3451182504723773
# 0.00014753614577624565
# 0.34526578661815355
# 0.0
```
where `vis` is the value of the visibility function, `phi` is the angle (in radians) drawn between the two Earth-centered-inertial points, and `a1` and `a2` are intermediate construction angles. A value of `vis`>0 means that the two points have a direct LOS to each other.

### Example 2
If you just want to know if two points are visible to each other in a binary fashion, use `isVis`:
```python
[vis_bool] = isVis(r1, r2, earth_radius, extra_height)
print(vis_bool)
# True
```

### Example 3
A series of visibility function values can be represented as a couple of `ndarray`s or an `IntervalTree` via the `zeroCrossingFit` function. This is handy if you want to calculate visibility windows between two objects.
```python
t = array([0, 1, 2, 3, 4]) # time vector
vis = array([-1, -0.1, 0.5, 4, 2]) # objects become visible to each other between t[1] and t[2]
[crossings, rise_set, vis_tree] = zeroCrossingFit(vis, t)
print(crossings)
print(rise_set)
print(vis_tree)

# Prints:
# [1.40896106] 
# [1.]
# tree=IntervalTree([Interval(1.4089610649024726, 4)])
```
Where `crossings` is a list of times at which the visibility function value crosses zero, `rise_set` indicates the direction of the crossing (1=rise, -1=set), and `tree` is an `IntervalTree` indicating time windows during which the visibility function value is positive. See the [IntervalTree package](https://github.com/chaimleib/intervaltree) on GitHub for details on its structure.

### Example 4
If the two objects never see each other, the returned arrays and `IntervalTree` are empty.
```python
vis = array([-1, -0.1, -0.5, -4, -2]) 
[crossings, rise_set, vis_tree] = zeroCrossingFit(vis, t)
print(crossings)
print(rise_set)
print(vis_tree)
# []
# []
# IntervalTree()
```

### Example 5
You can assign an identifier to `Interval`s within an `IntervalTree`. This is useful if you combine multiple `IntervalTree`s representing more than two objects.
```python
vis1 = array([-1, -0.1, 0.5, 4, 2])
vis2 = array([-2, -1, -0.5, 1, 1.1]) 
[_, _, vis_tree1] = zeroCrossingFit(vis1, t, "pair1")
[_, _, vis_tree2] = zeroCrossingFit(vis2, t, "pair2")
combined_tree = vis_tree1 | vis_tree2
print(vis_tree1)
print(vis_tree2)
print(combined_tree)
# tree=IntervalTree([Interval(1.4089610649024726, 4, 'pair1)])
# tree=IntervalTree([Interval(2.328702338492417, 4, 'pair2')])
# IntervalTree([Interval(1.4089610649024726, 4, 'pair1'), Interval(2.328702338492417, 4, 'pair2')])

```
## Citations:
- Alfano, Salvatore & Jr, Negron, & Moore, Jennifer. (1992). Rapid Determination of Satellite Visibility Periods. Journal of The Astronautical Sciences. Vol. 40, April-June, pp 281-296. 
- Lawton, J. A.. (1987). Numerical Method for Rapidly Determining Satellite-Satellite and Satellite-Ground Station In-View Periods. Journal of Guidance, Navigation and Control. Vol. 10, January-February, pp. 32-36
- Chaim Leib Halbert's IntervalTree package on GitHub, https://pypi.org/project/intervaltree/#description

