#SpaceX telemetry capturing

An attempt to capture telemetry in realtime from a live video stream

• uses electron js to be able to do desktop capturing
• uses a very crude image overlap calculation to recognize characters

It is not much yet, but it does give some results:

getting it to run

• clone from github
• npm install
• npm start

workings

• play the spacex video in a frame, with a bit of transforms to get the interesting part up close
• use electron to capture the window and feed it back into a video element
• capture that video element to a few canvas elements, slicing out the data bits
• some thresholding to get the individual characters in greyscale
• calculate the similarity with predefined characters and get the best
• use that to guess the character

doing stuff with the data

The capture tries to send data over a local mhub-server. To set one up:

• (install nodejs)
• npm install -g mhub
• mhub-server

This launches an mhub server locally. If you want to see the data coming in, use

• mhub-client -l -o jsondata

This will give you a stream of data. With that you could

• pipe it to another utility
• listen to it with websockets
• listen to it with raw tcp sockets

Early results

• crs10 raw data
• /u/srokap created a csv out of this
• and a visualisation

some examples

Pipe it to file:

mhub-client -l -o jsondata > data.txt

Pipe it to mongodb:

mhub-client -l -o jsondata | mongoimport --db spacex --collection telemetry

Listen to the bus in a website:

ws = new WebSocket('ws://localhost:13900');

//subscribe to receive messages
ws.onopen = function() {
    ws.send(JSON.stringify({
        type: 'subscribe',
        node: 'default'
    }));
};

//handle messages received
ws.onmessage = function(msg) {
    console.log(JSON.parse(msg.data));
};

Listen with nodejs:

var MClient = require("mhub").MClient;

var client = new MClient("ws://localhost:13900");

//subscribe to receive messages
client.on("open", function() {
    client.subscribe("default");
});

//handle messages received
client.on("message", function(message) {
    console.log(message);
});

Listen with python:

import websocket
import json

#subscribe to receive messages
def on_open(ws):
    ws.send('{"type":"subscribe","node":"default"}')

#handle messages received
def on_message(ws, message):
    print json.loads(message)


ws = websocket.WebSocketApp("ws://localhost:13900",
                            on_message = on_message,
                            on_open = on_open)

ws.run_forever()

improvements / plans

• better character segmentation (it is currently not properly segmented when the video resolution is low)
• better character recognition, we may use a somewhat smarter algorithm, but it needs to be fast.
• more user friendly ui.