public int getReportDataInterval(long testId, String dataType, int imgWidth) {
		int pointCount = Math.max(imgWidth, MAX_POINT_COUNT);
		File reportFolder = config.getHome().getPerfTestReportDirectory(String.valueOf(testId));
		int interval = 0;
		File targetFile = new File(reportFolder, dataType + REPORT_DATA);
		if (!targetFile.exists()) {
			LOGGER.warn("Report {} for test {} does not exist.", dataType, testId);
			return 0;
		}

		try (LineNumberReader lnr = new LineNumberReader(new InputStreamReader(new FileInputStream(targetFile)))) {
			lnr.skip(targetFile.length());
			int lineNumber = lnr.getLineNumber() + 1;
			interval = Math.max(lineNumber / pointCount, 1);
		} catch (Exception e) {
			LOGGER.error("Failed to get report data for {}", dataType, e);
		}
		return interval;
	}
get the data point interval of report data. Use dataPointCount / imgWidth as the interval. if interval is 1, it
means we will get all point from report. If interval is 2, it means we will get 1 point from every 2 data.

@param testId   test id
@param dataType data type
@param imgWidth image width
@return interval interval value
ngrinder-controller/src/main/java/org/ngrinder/perftest/service/PerfTestService.java