patty111 / ISS-Tracker

International Space Station Tracking CLI app

ISS Real Time Tracking

• First Attempt: Cartesian Coordinates(笛卡爾座標)
  

The trajectory was strange, so I changed to a better world map and use Mecator Projection instead

Result

result with different map width (120 and 540)

Trajectory for 7 hrs

Mecator Projection

It is impossible to create a 100% precise 2D map . It will have some error regardless.

My convertion works well to about latitude between ±70°.

Convert from (latitude, longitude)

Convert geographic coordinates into pixel coordinates on my 2D map

1. Get radians from degrees

longitude_rad = lon * math.pi / 180
latitude_rad = lat * math.pi / 180

2. Get scale factor to fit my map size

x_scale = map_width / 2 / math.pi
y_scale = map_height / 2 / math.pi

The longitude scales ranges between ± $pi$

For the latitude part:

Theoretically, Mercator projection can range from $-infinity$ to $+infinity$, maps usually cut of around 85°. This is why places near poles will have distortions.
Numbers range around 3~4 can substitute pi for better fitting different latitude or maps. Here I use pi for general.

3. Get x, y coordinates on 2D map using Mercator projection

x = map_width / 2 + x_scale * longitude_radians
y = map_height / 2 - y_scale * math.log((1 + math.sin(latitude_radians)) / (1 - math.sin(latitude_radians)))

map_width(map_height) / 2 centers the map around latitude/longitude = 0

In my source code are some commented-out lines. I tried to calculate the y coordinates by taking into account the distortion of the Mercator projection, instead of using a constant scale factor($pi$), to get a more accurate map, but the result did not work well for my map.

Params

• MAP_Width: My preference is around 540
• MAP_Height: int(ratio * MAP_Width * 0.4), you can change the number to anything you like
• call_freq: by default the app will send request to the API endpoint every 10 seconds.
• history_queue_max_size: modify this to show longer/shorter trajectory (default 3 hrs).

Build

1. Create virtual env
   >python -m venv env
2. Get in the env
   >.\env\Scripts\activate
3. Install dependencies
   >pip install -r requirements.txt

Steps 1 and 2 may vary on differnt OS

Reference

• Wikipedia