gdal找到dem中距离待求点最近的已知高程点c++

可以使用GDAL库中的GDALRasterBand类来实现这个功能。以下是一个简单的示例代码：

#include <iostream>
#include "gdal_priv.h"
#include "cpl_conv.h" // for CPLMalloc()

int main()
{
    // Open the DEM file
    GDALAllRegister();
    GDALDataset *pDataset = (GDALDataset *) GDALOpen("dem.tif", GA_ReadOnly);
    if (pDataset == NULL)
    {
        std::cerr << "Failed to open DEM file!" << std::endl;
        return 1;
    }

    // Get the raster band
    GDALRasterBand *pBand = pDataset->GetRasterBand(1);

    // Get the geo-transform
    double adfGeoTransform[6];
    pDataset->GetGeoTransform(adfGeoTransform);

    // Define the point to query
    double x = 123.45;
    double y = 67.89;

    // Convert the point to pixel coordinates
    int nPixel, nLine;
    pBand->GetGeoTransform(adfGeoTransform, x, y, &nPixel, &nLine);

    // Read the pixel value
    float fValue;
    pBand->RasterIO(GF_Read, nPixel, nLine, 1, 1, &fValue, 1, 1, GDT_Float32, 0, 0);

    // Print the pixel value
    std::cout << "Pixel value at (" << x << ", " << y << ") is " << fValue << std::endl;

    // Close the dataset
    GDALClose(pDataset);

    return 0;
}

该示例代码首先打开了DEM文件，然后获取了第一个波段（假设DEM只有一个波段）。接下来，它获取了DEM的地理变换，用于将点坐标转换为像素坐标。然后，它读取了像素值，并将其输出到控制台。

如果要找到离查询点最近的已知高程点，您可以在DEM中查询一系列点，并找到其中距离查询点最近的点。以下是一个示例代码：

#include <iostream>
#include "gdal_priv.h"
#include "cpl_conv.h" // for CPLMalloc()
#include <vector>
#include <cmath>

struct Point
{
    double x;
    double y;
    float z;
};

int main()
{
    // Open the DEM file
    GDALAllRegister();
    GDALDataset *pDataset = (GDALDataset *) GDALOpen("dem.tif", GA_ReadOnly);
    if (pDataset == NULL)
    {
        std::cerr << "Failed to open DEM file!" << std::endl;
        return 1;
    }

    // Get the raster band
    GDALRasterBand *pBand = pDataset->GetRasterBand(1);

    // Get the geo-transform
    double adfGeoTransform[6];
    pDataset->GetGeoTransform(adfGeoTransform);

    // Define the query point
    double x = 123.45;
    double y = 67.89;

    // Convert the query point to pixel coordinates
    int nPixel, nLine;
    pBand->GetGeoTransform(adfGeoTransform, x, y, &nPixel, &nLine);

    // Define the search radius in pixels
    int nRadius = 10;

    // Define the search area in pixels
    int nLeft = nPixel - nRadius;
    int nTop = nLine - nRadius;
    int nWidth = 2 * nRadius + 1;
    int nHeight = 2 * nRadius + 1;

    // Read the pixel values in the search area
    std::vector<float> vecValues(nWidth * nHeight);
    pBand->RasterIO(GF_Read, nLeft, nTop, nWidth, nHeight, &vecValues[0], nWidth, nHeight, GDT_Float32, 0, 0);

    // Convert the search area to geographic coordinates
    std::vector<Point> vecPoints(nWidth * nHeight);
    for (int i = 0; i < nWidth; ++i)
    {
        for (int j = 0; j < nHeight; ++j)
        {
            int nIndex = i * nHeight + j;
            double x = adfGeoTransform[0] + (nLeft + i) * adfGeoTransform[1] + (nTop + j) * adfGeoTransform[2];
            double y = adfGeoTransform[3] + (nLeft + i) * adfGeoTransform[4] + (nTop + j) * adfGeoTransform[5];
            vecPoints[nIndex].x = x;
            vecPoints[nIndex].y = y;
            vecPoints[nIndex].z = vecValues[nIndex];
        }
    }

    // Find the point closest to the query point
    Point closestPoint;
    closestPoint.z = std::numeric_limits<float>::max();
    for (const auto &point : vecPoints)
    {
        double dx = point.x - x;
        double dy = point.y - y;
        double distance = std::sqrt(dx*dx + dy*dy);
        if (distance < nRadius && point.z < closestPoint.z)
        {
            closestPoint = point;
        }
    }

    // Print the closest point
    std::cout << "Closest point to (" << x << ", " << y << ") is (" << closestPoint.x << ", " << closestPoint.y << ", " << closestPoint.z << ")" << std::endl;

    // Close the dataset
    GDALClose(pDataset);

    return 0;
}

该示例代码首先定义了要查询的点，并将其转换为像素坐标。然后，它定义了一个搜索半径，并使用该半径在DEM中查询像素值。接下来，它将搜索区域中的每个像素转换为地理坐标，并将其保存在一个点向量中。然后，它找到最靠近查询点的点，并将其输出到控制台。

请注意，此示例代码仅在搜索区域内搜索点。如果您需要在整个DEM中搜索点，则需要更改搜索区域并读取整个DEM，这可能会非常耗时。