Figure 2. Details of the pre-processing approach for the raw COVID-19 surveillance data. The original database signal interpolated by the sample-and-hold technique is shown in a staircase-shaped discrete-time signal, where each X-mark means a daily sample. With each new information arrival (marked with O) a new step is formed. In blue is the piecewise linear signal, formed by line segments connecting the unevenly time series samples. From resampling and smoothing with moving average digital filter the piecewise linear signal, the nowcasted signal was derived, shown in red. The nowcasted signal does not necessarily cut through the information arrival points (O).
