GeoTools栅格数据分析之图像变化检测

功能需求：给定同一区域不同时间的无人机影像数据，求出区域内影像变化部分，并矢量化成GeoJSON返回给前端。

1.将两幅图像进行相减与二值化操作

    public GridCoverage2D tiffSubtract(String sourceTiffPath, String targetTiffPath, float diffLimit)
            throws IOException {
        File sourceTiff = new File(sourceTiffPath);
        File targetTiff = new File(targetTiffPath);

        if (!sourceTiff.exists() || !targetTiff.exists()) {
            throw new FileNotFoundException(sourceTiffPath + " or " + targetTiffPath + " do not exist!");
        }

        // 中间数据tiff存储路径
        String tempTiff = sourceTiff.getParent() + File.separator + "output.tiff";
        // tiff文件坐标系设置
        Hints tiffHints = new Hints();
        tiffHints.add(new Hints(Hints.FORCE_LONGITUDE_FIRST_AXIS_ORDER, Boolean.TRUE));
        tiffHints.add(new Hints(Hints.DEFAULT_COORDINATE_REFERENCE_SYSTEM, DefaultGeographicCRS.WGS84));

        GeoTiffReader sourceReader = new GeoTiffReader(sourceTiff, tiffHints);
        GeoTiffReader targetReader = new GeoTiffReader(targetTiff, tiffHints);

        GridCoverage2D sourceCoverage = sourceReader.read(null);
        GridCoverage2D targetCoverage = targetReader.read(null);
        RenderedImage sourceImage = sourceCoverage.getRenderableImage(0, 1).createDefaultRendering();
        RenderedImage targetImage = targetCoverage.getRenderableImage(0, 1).createDefaultRendering();
        Raster sourceRaster = sourceImage.getData();
        Raster targetRaster = targetImage.getData();

        int width = sourceRaster.getWidth();
        int height = sourceRaster.getHeight();
        // System.out.println("pixels : width:" + width + ";height:" + height);

        Envelope2D sourceEnv = sourceCoverage.getEnvelope2D();

        float[][] difference = new float[height][width];
        float s;
        float t;
        // 修改算法,提取差异值大于阈值的部分
        // 将图像二值化
        for (int x = 0; x < width - 1; x++) {
            for (int y = 0; y < height - 1; y++) {
//              System.out.println("x:" + x + ";y:" + y);
                s = sourceRaster.getSampleFloat(x, y, 1);
                t = targetRaster.getSampleFloat(x, y, 1);
                float diff = t - s;
                if (diff > diffLimit) {
                    difference[y][x] = 100f;
                } else {
                    difference[y][x] = 0f;
                }
            }
        }

        GridCoverageFactory factory = new GridCoverageFactory();
        GridCoverage2D outputCoverage = factory.create("subtractTiff", difference, sourceEnv);
        GeoTiffWriter writer = new GeoTiffWriter(new File(tempTiff));
        writer.write(outputCoverage, null);
        writer.dispose();
        return outputCoverage;
    }

2.调用geoTools的PolygonExtractionProcess将图像相减操作结果进行矢量化

    public String polygonExtraction(GridCoverage2D tiffCoverage, String shpPath)
            throws MismatchedDimensionException, IndexOutOfBoundsException, NoSuchAuthorityCodeException,
            ParseException, FactoryException, TransformException, SchemaException, IOException {
        PolygonExtractionProcess process = new PolygonExtractionProcess();
        SimpleFeatureCollection features = process.execute(tiffCoverage, 0, Boolean.TRUE, null, null, null, null);

        features = this.polygonPostprocess(features, 10d);

        SimpleFeatureType type = features.getSchema();

//      ShapeFileWriter.INSTANCE.write(shpPath, features, type);
        this.toGeoJSON(features);

        return shpPath;
    }

3.对矢量化后的多边形对象进行过滤，删除面积过小的细碎多边形

private SimpleFeatureCollection polygonPostprocess(SimpleFeatureCollection features, double aeraLimit)
            throws IndexOutOfBoundsException, ParseException, NoSuchAuthorityCodeException, FactoryException,
            MismatchedDimensionException, TransformException, SchemaException {
        //坐标转换,从4326转成3857
        CoordinateReferenceSystem dataCRS = DefaultGeographicCRS.WGS84;
        CoordinateReferenceSystem targerCRS = CRS.decode("EPSG:3857");
        boolean lenient = true; // allow for some error due to different datums
        MathTransform transform = CRS.findMathTransform(dataCRS, targerCRS, lenient);

        final SimpleFeatureType TYPE = DataUtilities.createType("Location",
                "the_geom:Polygon:srid=3857,DN:String,Aera:Double");

        List<SimpleFeature> projectedFeatureList = new ArrayList<SimpleFeature>();

        GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
        WKTReader reader = new WKTReader(geometryFactory);
        SimpleFeatureBuilder builder = new SimpleFeatureBuilder(TYPE);

        SimpleFeatureIterator iterator = features.features();
        try {
            while (iterator.hasNext()) {
                SimpleFeature feature = iterator.next();
                Polygon polygon = (Polygon) feature.getDefaultGeometry();
                polygon = (Polygon) JTS.transform(polygon, transform);
                double aera = polygon.getArea();
                // 多边形面积大于阈值
                if (aera >= aeraLimit) {
                    builder.add(polygon);
                    builder.add(feature.getAttribute(1).toString());
                    builder.add(aera);
                    SimpleFeature tempFeature = builder.buildFeature(null);
                    projectedFeatureList.add(tempFeature);
                }
            }
        } finally {
            iterator.close();
        }

        System.out.println(projectedFeatureList.size());
        return new ListFeatureCollection(TYPE, projectedFeatureList);
    }

4.将最终结果以GeoJSON格式返回

    private void toGeoJSON(SimpleFeatureCollection featureCollection) {
        SimpleFeatureIterator it = featureCollection.features();
        GeoJsonWriter geoJsonWriter = new GeoJsonWriter();
        
        while(it.hasNext()) {
            SimpleFeature tempFeature = it.next();
            
            Geometry geometry = (Geometry) tempFeature.getDefaultGeometry();
            
            String json = geoJsonWriter.write(geometry);
            
            System.out.println(json);
        }
    }