geotools resample时像素变得过大 怎么控制

在 Geotools 中进行重采样时，由于源图像和目标图像的分辨率不同，可能会导致像素变大或变小。为了控制像素大小，可以使用 Geotools 提供的重采样器对象进行设置。以下是一个示例代码，可以将源图像重采样为目标图像，同时控制像素大小。

import org.geotools.coverage.grid.GridCoverage2D;
import org.geotools.coverage.processing.AbstractProcessor;
import org.geotools.coverage.processing.CoverageProcessor;
import org.geotools.factory.Hints;
import org.geotools.gce.arcgrid.ArcGridWriter;
import org.geotools.gce.arcgrid.ArcGridWriterFactory;
import org.geotools.gce.geotiff.GeoTiffWriter;
import org.geotools.gce.geotiff.GeoTiffWriter2;
import org.geotools.geometry.jts.ReferencedEnvelope;
import org.geotools.referencing.CRS;
import org.geotools.referencing.crs.DefaultGeographicCRS;
import org.geotools.referencing.operation.DefaultMathTransformFactory;
import org.geotools.referencing.operation.transform.AffineTransform2D;
import org.geotools.resample.ResampleProcess;
import org.geotools.util.factory.Hints;
import org.opengis.parameter.GeneralParameterValue;
import org.opengis.parameter.ParameterValueGroup;
import org.opengis.referencing.crs.CoordinateReferenceSystem;

import javax.media.jai.Interpolation;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.HashMap;
import java.util.Map;

public class ResampleImage {
    public static void main(String[] args) throws Exception {
        File sourceFile = new File("/path/to/source/raster.tif");
        File targetFile = new File("/path/to/target/raster.tif");

        // 加载源图像
        GridCoverage2D sourceCoverage = loadGridCoverage(sourceFile);

        // 目标图像的分辨率（像素大小）
        double targetPixelSize = 10.0;

        // 计算目标图像的宽度和高度
        int targetWidth = (int) Math.round(sourceCoverage.getEnvelope().getWidth() / targetPixelSize);
        int targetHeight = (int) Math.round(sourceCoverage.getEnvelope().getHeight() / targetPixelSize);

        // 目标图像的范围和分辨率
        CoordinateReferenceSystem targetCRS = DefaultGeographicCRS.WGS84;
        ReferencedEnvelope targetEnvelope = new ReferencedEnvelope(sourceCoverage.getEnvelope().getMinimum(0),
                sourceCoverage.getEnvelope().getMaximum(0), sourceCoverage.getEnvelope().getMinimum(1),
                sourceCoverage.getEnvelope().getMaximum(1), targetCRS);
        double[] targetResolution = { targetPixelSize, targetPixelSize };

        // 创建目标图像
        GridCoverage2D targetCoverage = createGridCoverage(targetWidth, targetHeight, targetEnvelope, targetResolution,
                targetCRS);

        // 创建重采样器
        ResampleProcess resampleProcess = new ResampleProcess();
        ParameterValueGroup params = resampleProcess.getParameters();
        params.parameter("Source").setValue(sourceCoverage);
        params.parameter("Destination").setValue(targetCoverage);
        params.parameter("InterpolationType").setValue(Interpolation.INTERP_BICUBIC);
        CoverageProcessor coverageProcessor = new CoverageProcessor(new Hints(Hints.FORCE_LONGITUDE_FIRST_AXIS_ORDER,
                Boolean.TRUE));
        coverageProcessor.addCoverageProcessor(resampleProcess);
        GridCoverage2D resampledCoverage = (GridCoverage2D) coverageProcessor.doOperation(params);

        // 写入目标图像
        writeGridCoverage(resampledCoverage, targetFile);
    }

    public static GridCoverage2D loadGridCoverage(File file) throws Exception {
        // 加载栅格文件
        Map<String, Object> loadParams = new HashMap<>();
        loadParams.put("url", file.toURI().toURL());
        GridCoverage2D coverage = (GridCoverage2D) new ArcGridReader().read(loadParams);
        return coverage;
    }

    public static GridCoverage2D createGridCoverage(int width, int height, ReferencedEnvelope envelope,
            double[] resolution, CoordinateReferenceSystem crs) throws Exception {
        // 创建栅格文件
        BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_USHORT_GRAY);
        double[] matrix = new double[] { resolution[0], 0, 0, -resolution[1], envelope.getMinX(), envelope.getMaxY() };
        AffineTransform2D gridToWorld = new AffineTransform2D(matrix);
        GridCoverageFactory factory = new GridCoverageFactory();
        GridCoverage2D coverage = factory.create("Coverage", bufferedImage, envelope);
        coverage = (GridCoverage2D) Operations.DEFAULT.resample(coverage, gridToWorld, Interpolation.INTERP_BICUBIC);
        return coverage;
    }

    public static void writeGridCoverage(GridCoverage2D coverage, File file) throws Exception {
        // 写入栅格文件
        Map<String, Object> saveParams = new HashMap<>();
        saveParams.put("url", file.toURI().toURL());
        saveParams.put("gridsize", coverage.getRenderedImage().getData().getWidth());
        saveParams.put("writeGeoTIFFTags", true);
        saveParams.put("forceBigTiff", true);
        ArcGridWriterFactory writerFactory = new ArcGridWriterFactory();
        ArcGridWriter writer = (ArcGridWriter) writerFactory.createWriter(saveParams);
        writer.write(coverage, saveParams);
    }
}

在这个示例中，我们首先加载源图像，然后根据目标图像的分辨率计算目标图像的宽度和高度。接下来，我们创建目标图像的范围和分辨率，并使用它们创建目标图像。然后，我们使用重采样器进行重采样，并将结果写入目标图像文件。

注意，在创建目标图像时，我们使用了一个 AffineTransform2D 对象来将网格坐标映射到世界坐标。通过调整这个对象的矩阵，可以控制像素的大小。在本示例中，我们将像素大小设置为目标图像的分辨率。

如果您需要进一步控制像素大小，可以根据需要调整 AffineTransform2D 对象的矩阵。同时，您还可以尝试使用不同的重采样算法，以获得更好的结果。