Take a look the detrended brightness graph you made in the preceding chapter.

There is a clear band of data. I.e. regions where most of the data-points lie. But what also stands out enormous are outliers. For example, most points are below 50, but some shoot out all the way to 600. They are clearly erroneous.

There are various reasons how these outliers can occur. Some are the results of satellite maneuvers. What ever there origin, in this chapter we will filter those outliers.

We are defining a threshold beyond which we will discard our data.

const threshold = 200.00;

Next we will use that threshold to in our data to discard our actual data. Discarding can be achieved by return null instead of an array of data.

const time = parseFloat(data[0]);
const brightness = parseFloat(data[1]);
const trend = parseFloat(data[2]);
const difference = parseFloat(data[3]);

if (Math.abs(difference) <= threshold) {
    return data;
} else {
    return null;
}

The algorithm above depends on a certain threshold. What value should we use? Try some different values and try to get a feel for what works. Discuss your choices with somebody else.