PCM-net: Phase-change material data collection

How the material data are collected

Material data can be readily obtained from published research articles. Research articles provide the data in the form of graphical plots (visualizations) or alternatively through supplementary datasets (less widely available). Since the former does not directly provide the dataset in numbers, it requires a conversion process from visual graph plot images back to the original dataset. While a range of chart recognition tools are available for converting graphical images to datasets (numbers), it should be noted that the conversion process is hard to automatize and requires manual work. For example, WebPlotDigitizer can generate the original dataset from a given plot image file by extracting the plot line. WebPlotDigitizer automatizes the process of detecting the color difference between the line and the background, and extracts the plot line. But users still need to manually specify the details of the plot with a mouse or a pen input device, such as the plot line area, x-y axes, and the scale of the axes. Extracting coordinate data from line plots using WebPlotDigitizer Below are the steps for using WebPlotDigitizer to extract the desired x-y coordinate values for a line plot. Figure describes how users extract a characteristic dataset for a PCM from a plot image using WebPlotDigitizer.

Using WebPlotDigitizer to extract the data


Figure 1. Extracting x-y coordinates data from a line plot.

Below are the steps for using WebPlotDigitizer to extract the desired x-y coordinate values for a line plot. Figure 1 describes how users extract a characteristic dataset for a PCM from a plot image using WebPlotDigitizer.
  1. Upload the plot image file to WebPlotDigitizer: Crop the plot image file (Figure 1(a)) from the paper and upload it to the WebPlotDigitizer web application
  2. Set up the basic axis scale information. In this example, wavelength for the x-axis has a range between 0 and 3 (eV). Refraction index on the y-axis has a range between 0 and 55.
  3. Specify the plot line color and mark the plot line: WebPlotDigitizer distinguishes the plot line from the background using the difference in colors. In this example, the purple color of the plot line (Ge15Sb85) is set to the foreground color. Then users need to roughly mark the background area (denoted as yellow color in Figure 1(b)) that WebPlotDigitizer processes for extracting the plot line with the mouse operation.
  4. Data extraction and refinement: WebPlotDigitizer then extracts the plot line with the specified foreground color and generates points on the line to be converted into (x, y) coordinate values. From the figure, it can be seen that red dots are generated on the purple plot line and each dot corresponds to the (x, y) coordinate value of the extracted plot line. WebPlotDigitizer has options available for data extraction methods and "X step with interpolation option" is selected where users can specify ΔX step value on the x-axis. The reason for the option selection is that it can generate the y-axis value mapped one-to-one for an x-axis value and the y-axis value estimation using linear interpolation techniques can be more accurate for a curvy line plot. In this example, when ΔX is set to 0.05, WebPlotDigizier extracts the corresponding y coordinates for x coordinates 0, 0.05, 0.10, and so on up to 3. In Figure 1(c), it can be seen that WebPlotDigitizer is able to generate extracted red dots on the plot line while there seems to be slight errors visually identifiable in the y-axis values on the left and rightmost sides. These errors can be modified manually by clicking on each dot and adjusting the y-axis value.
  5. Export the extracted (x, y) coordinate values to a file: Users can export the extracted dataset as a comma separated values (CSV) file format. Exported data are then stored in the MySQL database.