public void readElementTable(String filename) {
		// open elementTableFile and save element to ElementTable array
		Workbook elementBook = null;
		try {
			elementBook = Workbook.getWorkbook(new File(filename));
		} catch (Exception e) {
			e.printStackTrace();
		}

		if (elementBook == null) {
			System.err.println("open element table file failed!");
			System.exit(-5);
		}

		Sheet sheet = elementBook.getSheet(0); // get the fist sheet

		int rowNum = sheet.getRows();

		int columnNum = sheet.getColumns();

		ElementProperty[] element = new ElementProperty[rowNum - 1];

		int xMaxColumn = -1;
		int xMinColumn = -1;
		int yMaxColumn = -1;
		int yMinColumn = -1;

		for (int i = 1; i < columnNum; i++) {
			String cellCnt = sheet.getCell(i, 0).getContents();
			// System.out.println(cellCnt);
			if (cellCnt.compareToIgnoreCase("xMax") == 0) {
				xMaxColumn = i;
			} else if (cellCnt.compareToIgnoreCase("xMin") == 0) {
				xMinColumn = i;
			} else if (cellCnt.compareToIgnoreCase("yMax") == 0) {
				yMaxColumn = i;
			} else if (cellCnt.compareToIgnoreCase("yMin") == 0) {
				yMinColumn = i;
			}

			// System.out.println("xMax="+xMaxColumn+"xMin="+xMinColumn+"yMax="+yMaxColumn+"yMin="+yMinColumn);
		}

		for (int i = 1; i < rowNum; i++) {
			int index = i - 1;
			element[index] = new ElementProperty();
			element[index].elementName = sheet.getCell(0, i).getContents();
			element[index].xMax = Double.parseDouble(sheet.getCell(xMaxColumn,
					i).getContents());
			element[index].xMin = Double.parseDouble(sheet.getCell(xMinColumn,
					i).getContents());
			element[index].yMax = Double.parseDouble(sheet.getCell(yMaxColumn,
					i).getContents());
			element[index].yMin = Double.parseDouble(sheet.getCell(yMinColumn,
					i).getContents());
			// System.out.println("element["+index+"].elementName="+element[index].elementName+"element["+index+"].xMax="+element[index].xMax);
			// System.out.println("element["+index+"].yMin="+element[index].yMin+"element["+index+"].yMax="+element[index].yMax);
		}

		elementBook.close();
		
		elements = element;
	}