fftfreqcenter (Python/JS)

def fftfreqcenter2(samples, speed_step, doppler_min_speed):
    speeds = [doppler_min_speed]
    for _ in range(samples):
        speeds.append(speeds[-1] + speed_step)
    return speeds



function fftfreqcenter(samples, speed_step, doppler_min_speed) {
    var result = [doppler_min_speed];
    for (var i=1; i < samples; i++) {
        result[i] = result[i-1] + speed_step
        }
    return result;
    }



You receive every 20th frame a state over websocket with following content:
"state": {"mode": "CW", "sample_rate": 122880, "window_size": 512, "bandwidth": 180000000, "fft": true, "window_function": "hanning", "vco_signal": null, "doppler": {"min_speed": null, "max_speed": null}, "motor": {"start": 0, "stop": 360, "run": false}}}

Now I see it, min_speed and max_speed should never be null. After fixing my bug they have always a valid value.

To calculate the speed for the distance axis (X on A, Y on B), you need to know the number of samples, speed_step (in m/s) and doppler_min_speed as offset.


fftfreqcenter(14, 3.0, 0);

# Array(14) [ 0, 3, 6, 9, 12, 15, 18, 21, 24, 27, … ]
This means the first sample is for 0 m/s, second sample 3.0 m/s ...
After starting the server, it's set automatically to it's maximum range (from negative to 0 to positive).






















######################OLD########################################

# I have copied parts from:
# https://github.com/numpy/numpy/blob/v1.15.0/numpy/fft/helper.py#L124-L169
#
# The task was, to have a fftfreqcenter function in JavaScript, which
# uses instead of a sampling space, a provided value, which can be anything
# In our case: Distance (FMCW) or Speed (CW)

def fftfreqcenter(samples, multiplicator):
    NP = (samples-1) // 2 + 1
    NN = -samples // 2
    pos = list(range(0, NP))
    neg = list(range(NN, 0))
    result = neg + pos
    return [r * multiplicator for r in result]


function fftfreqcenter(samples, multiplicator) {
    var NP = Math.floor((samples - 1) / 2 + 1);
    var NN = Math.floor(-(samples / 2));
    var pos = [];
    var neg = [];
    var idx = 0;
    for (var i=0; i < NP; i++) {
        pos[idx] = i * multiplicator;
        idx++;
        }
    idx = 0;
    for (var i=NN; i < 0; i++) {
        neg[idx] = i * multiplicator;
        idx++;
        }
    return neg.concat(pos);
    }

// fftfreqcenter(16, 1)
// [-8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7]

fftfreqcenter(16, 1);