注：DEM坡度算法参考这里，具体使用geoTools实现

1.计算指定像素坐标点的坡度

    public float calcSlope(int cellX, int cellY, PlanarImage image) throws IOException {
        DecimalFormat df = new DecimalFormat("#.0000");
        final int[] dest = null;
        int e = image.getTile(image.XToTileX(cellX), image.YToTileY(cellY)).getPixel(cellX, cellY, dest)[0];
        int e1 = image.getTile(image.XToTileX(cellX - 1), image.YToTileY(cellY)).getPixel(cellX - 1, cellY, dest)[0];
        int e2 = image.getTile(image.XToTileX(cellX), image.YToTileY(cellY - 1)).getPixel(cellX, cellY - 1, dest)[0];
        int e3 = image.getTile(image.XToTileX(cellX + 1), image.YToTileY(cellY)).getPixel(cellX + 1, cellY, dest)[0];
        int e4 = image.getTile(image.XToTileX(cellX), image.YToTileY(cellY + 1)).getPixel(cellX, cellY + 1, dest)[0];
        int e5 = image.getTile(image.XToTileX(cellX - 1), image.YToTileY(cellY - 1)).getPixel(cellX - 1, cellY - 1,
                dest)[0];
        int e6 = image.getTile(image.XToTileX(cellX + 1), image.YToTileY(cellY - 1)).getPixel(cellX + 1, cellY - 1,
                dest)[0];
        int e7 = image.getTile(image.XToTileX(cellX + 1), image.YToTileY(cellY + 1)).getPixel(cellX + 1, cellY + 1,
                dest)[0];
        int e8 = image.getTile(image.XToTileX(cellX - 1), image.YToTileY(cellY + 1)).getPixel(cellX - 1, cellY + 1,
                dest)[0];
        double slopeWE = ((e8 + 2 * e1 + e5) - (e7 + 2 * e3 + e6)) / (8 * 2041.823085);// 东西方向坡度
        double slopeNW = ((e7 + 2 * e4 + e8) - (e6 + 2 * e2 + e5)) / (8 * 2041.823085);// 南北方向坡度
        double slope = 100*(Math.sqrt(Math.pow(slopeWE, 2) + Math.pow(slopeNW, 2)));
        return Float.parseFloat(df.format(slope));
    }

2.DEM数据测试用例

    @Test
    public void testCalcSlope() throws NoSuchAuthorityCodeException, FactoryException, IOException {
        String path = "D:\\workData\\geotiff\\testTiff.tif";
        String outputPath = "D:\\workData\\geotiff\\output.tif";
        File file = new File(path);
        // 设置tiff影像默认设置
        Hints tiffHints = new Hints();
        tiffHints.add(new Hints(Hints.FORCE_LONGITUDE_FIRST_AXIS_ORDER, Boolean.TRUE));
        // 默认坐标系EPSG:3857 
//      tiffHints.add(new Hints(Hints.DEFAULT_COORDINATE_REFERENCE_SYSTEM, CRS.decode("EPSG:4326")));
        tiffHints.add(new Hints(Hints.DEFAULT_COORDINATE_REFERENCE_SYSTEM, DefaultGeographicCRS.WGS84));

        GeoTiffReader reader = new GeoTiffReader(file, tiffHints);

        GridCoverage2D coverage = reader.read(null);
        Envelope env = coverage.getEnvelope();
        PlanarImage image = (PlanarImage) coverage.getRenderedImage();
        int width = image.getWidth(); // Image Width
        int height = image.getHeight(); // Image Height

        // 计算每个栅格的坡度
        float[][] slopeData = new float[height][width];
        for (int i = 1; i < height + 1; i++) {
            for (int j = 1; j < width + 1; j++) {
                float slope = SlopeUtil.INSTANCE.calcSlope(j, i, image);
                slopeData[i - 1][j - 1] = slope;
            }
        }

        GridCoverageFactory factory = new GridCoverageFactory();
        GridCoverage2D outputCoverage = factory.create("test", slopeData, env);
        GeoTiffWriter writer = new GeoTiffWriter(new File(outputPath));
        writer.write(outputCoverage, null);
        writer.dispose();
    }