（C++）GDAL学习笔记——2 计算NDVI并用阈值法提取植被

又经过了几天的学习，完成了第二个实验，相较于第一个实验，第二个实验在进行的过程中确实遇到了一些问题，耗时也更长，不过总归是完成了。

任务

计算植被指数，并通过阈值法提取植被

代码

注：部分函数的注释由于在第一篇帖子里出现了，这里就不赘言了
程序的结构如下：

主函数proj2.cpp

/*
* 用于学习GDAL编程 实验二 计算植被指数，并通过阈值法提取植被
* 时间 20210705
* 本次实验采用的影像为四波段的影像
*/

#include
#include "gdal.h"
#include "gdal_priv.h"
#include "Func.h"

using namespace std;

int main()
{
	// 读取影像
	char* openpath = "D:\\Practice\\org\\exp2.tif";

	GDALDataset* mDataset;
	GDALAllRegister();

	// 只读方式打开
	mDataset = (GDALDataset*)GDALOpen(openpath, GA_ReadOnly);

	if (mDataset == NULL)
	{
		cout << "未能正确加载数据!!!" << endl;
		system("pause");
		GDALDestroyDriverManager();
	}
	// 获取影像数据
	int mX = mDataset->GetRasterXSize();
	int mY = mDataset->GetRasterYSize();
	GDALDataType mImgDataType = mDataset->GetRasterBand(1)->GetRasterDataType();

	// 获取影像的地理信息和投影信息
	double geoInformation[6];
	mDataset->GetGeoTransform(geoInformation);
	const char* gdalProjection = mDataset->GetProjectionRef();

	// 新建一个驱动，影像格式为GTiff
	GDALDriver* hDriver = GetGDALDriverManager()->GetDriverByName("GTiff");

	// 调用CalcuNDVI 进行计算，需要先建立一个数据集保存NDVI结果,NDVI中的数据类型是float
	char* savepath = "D:\\Practice\\res\\exp2_ndvi.tif";
	GDALDataset* mNDVIset = hDriver->Create(savepath, mX, mY, 1, GDT_Float32, NULL);

	cout << "正在计算NDVI" << endl;

	CalcuNDVI(mDataset, mNDVIset);

	// 将影像的地理信息写到NDVI数据集中
	mNDVIset->SetGeoTransform(geoInformation);
	mNDVIset->SetProjection(gdalProjection);


	// 调用ExtractVegetation进行提取，需要先建立一个数据集保存提取结果
	char* savepath2 = "D:\\Practice\\res\\exp2_vegetation.tif";
	GDALDataset* mVegetationSet = hDriver->Create(savepath2, mX, mY, 4, mImgDataType, NULL);

	cout << "正在提取植被区域！！！" << endl;

	ExtractVegetation(mDataset, mNDVIset, mVegetationSet, 0.35, 0.7);

	// 将影像的地理信息写到植被数据集中
	mVegetationSet->SetGeoTransform(geoInformation);
	mVegetationSet->SetProjection(gdalProjection);


	// 关闭数据集，释放内存
	GDALClose(mDataset);
	GDALClose(mNDVIset);
	GDALClose(mVegetationSet);
	GDALDestroyDriverManager();

	cout << "处理结束！！！" << endl;
	getchar();

	return 0;
}

头文件Func.h

#pragma once
#include 
#include "gdal.h"
#include "gdal_priv.h"
#include "ogr_spatialref.h"

using namespace std;

// 计算NDVI,mDataset为输入数据，mNDVI为计算结果
void CalcuNDVI(GDALDataset* mDataset,GDALDataset* &mNDVI);

// 利用NDVI，采用阈值分割的方式提取植被,mDataset为原始影像，
// mNDVIset为NDVI数据，其值在[-1,+1]之间，VegetationSet为提取出的植被数据,th1为低阈值，th2为高阈值
void ExtractVegetation(GDALDataset* mDataset, GDALDataset* mNDVIset, GDALDataset* &VegetationSet, float th1, float th2);

函数文件 Func.cpp

#include "Func.h"


void CalcuNDVI(GDALDataset* mDataset, GDALDataset* &mNDVIset)
{
	// 获取影像的参数
	int mX = mDataset->GetRasterXSize();
	int mY = mDataset->GetRasterYSize();
	int mDataType = mDataset->GetRasterBand(1)->GetRasterDataType();
	
	// 将影像中的四个波段取出,分别为NIR，R,G,B
	GDALRasterBand* mB = mDataset->GetRasterBand(1);
	GDALRasterBand* mG = mDataset->GetRasterBand(2);
	GDALRasterBand* mR = mDataset->GetRasterBand(3);
	GDALRasterBand* mNIR = mDataset->GetRasterBand(4);

	// 申请缓冲区
	float* RedBuf = (float*)CPLMalloc(sizeof(float)*mX*mY);
	float* NIRBuf = (float*)CPLMalloc(sizeof(float)*mX*mY);
	float* mNDVIband = (float*)CPLMalloc(sizeof(float)*mX*mY);



	// 从R和NIR波段中取出数据放到缓冲区
	mR->RasterIO(GF_Read, 0, 0, mX, mY, RedBuf, mX, mY, GDT_UInt32, 0, 0);
	mNIR->RasterIO(GF_Read, 0, 0, mX, mY, NIRBuf, mX, mY, GDT_UInt32, 0, 0);

	// 计算NDVI
	for (int i = 0; i < mY; i++)
	{
		for (int j = 0; j < mX; j++)
		{
			float r = RedBuf[i*mX + j];
			float nir = NIRBuf[i*mX + j];

			mNDVIband[i*mX + j] = (nir - r) / (nir + r);
		}
	}

	
	// 将计算结果写入NDVI的数据集中
	mNDVIset->GetRasterBand(1)->RasterIO(GF_Write, 0, 0, mX, mY, mNDVIband, mX, mY, GDT_Float32, 0, 0);
	
	// 释放内存
	CPLFree(RedBuf);
	CPLFree(NIRBuf);
	CPLFree(mNDVIband);

}


void ExtractVegetation(GDALDataset * mDataset, GDALDataset * mNDVIset, GDALDataset *& VegetationSet, float th1, float th2)
{
	// 获取影像参数
	int mX = mDataset->GetRasterXSize();
	int mY = mDataset->GetRasterYSize();
	GDALDataType mImgDataType = mDataset->GetRasterBand(1)->GetRasterDataType();
	GDALDataType mNDVIDataType = mNDVIset->GetRasterBand(1)->GetRasterDataType();

	// 获取原始影像的四个波段
	GDALRasterBand* mBand1 = mDataset->GetRasterBand(1);
	GDALRasterBand* mBand2 = mDataset->GetRasterBand(2);
	GDALRasterBand* mBand3 = mDataset->GetRasterBand(3);
	GDALRasterBand* mBand4 = mDataset->GetRasterBand(4);

	// 获取NDVI的波段
	GDALRasterBand* mNDVIBand = mNDVIset->GetRasterBand(1);

	// 申请缓冲区，用来保存原始波段和NDVI的数据
	unsigned short* mBandBuf1 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);
	unsigned short* mBandBuf2 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);
	unsigned short* mBandBuf3 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);
	unsigned short* mBandBuf4 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);

	float* mNDVIBandBuf = (float*)CPLMalloc(mX*mY * mNDVIDataType);

	// 将各个波段的数据放入对应的缓冲区
	mBand1->RasterIO(GF_Read, 0, 0, mX, mY, mBandBuf1, mX, mY, mImgDataType, 0, 0);
	mBand2->RasterIO(GF_Read, 0, 0, mX, mY, mBandBuf2, mX, mY, mImgDataType, 0, 0);
	mBand3->RasterIO(GF_Read, 0, 0, mX, mY, mBandBuf3, mX, mY, mImgDataType, 0, 0);
	mBand4->RasterIO(GF_Read, 0, 0, mX, mY, mBandBuf4, mX, mY, mImgDataType, 0, 0);

	mNDVIBand->RasterIO(GF_Read, 0, 0, mX, mY, mNDVIBandBuf, mX, mY, mNDVIDataType, 0, 0);

	// 申请缓冲区，用来保存提取出的植被区域
	unsigned short* mVegBand1 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);
	unsigned short* mVegBand2 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);
	unsigned short* mVegBand3 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);
	unsigned short* mVegBand4 = (unsigned short*)CPLMalloc(mX*mY * mImgDataType);

	//  通过阈值来提取植被区域
	for (int i = 0; i < mX*mY; i++)
	{
		// 若在阈值范围内，赋对应的值，若不在，赋值为0
		if (mNDVIBandBuf[i] >= th1&&mNDVIBandBuf[i] <= th2)
		{
			mVegBand1[i] = mBandBuf1[i];
			mVegBand2[i] = mBandBuf2[i];
			mVegBand3[i] = mBandBuf3[i];
			mVegBand4[i] = mBandBuf4[i];
		}
		else
		{
			mVegBand1[i] = 0;
			mVegBand2[i] = 0;
			mVegBand3[i] = 0;
			mVegBand4[i] = 0;
		}
	}

	// 把提取结果放到数据集中
	VegetationSet->GetRasterBand(1)->RasterIO(GF_Write, 0, 0, mX, mY, mVegBand1, mX, mY, mImgDataType, 0, 0);
	VegetationSet->GetRasterBand(2)->RasterIO(GF_Write, 0, 0, mX, mY, mVegBand2, mX, mY, mImgDataType, 0, 0);
	VegetationSet->GetRasterBand(3)->RasterIO(GF_Write, 0, 0, mX, mY, mVegBand3, mX, mY, mImgDataType, 0, 0);
	VegetationSet->GetRasterBand(4)->RasterIO(GF_Write, 0, 0, mX, mY, mVegBand4, mX, mY, mImgDataType, 0, 0);

	// 释放内存
	CPLFree(mBandBuf1);
	CPLFree(mBandBuf2);
	CPLFree(mBandBuf3);
	CPLFree(mBandBuf4);
	CPLFree(mNDVIBandBuf);
	CPLFree(mVegBand1);
	CPLFree(mVegBand2);
	CPLFree(mVegBand3);
	CPLFree(mVegBand4);
}

运行结果

影像数据：

NDVI：

提取植被：

结语

这一个实验中间确实卡了好几次，中间也在弄其他东西，以上的代码里面确实还有一些不合适的地方，但，，，总之结果是跑出来了ㄟ(川.一ㄟ)。后面再慢慢改进吧！主要还是对于C语言的理解不够，很多东西都是边用边学，一知半解的，看官也请多包涵。总之，任重而道远，慢慢学吧~~