哈夫变换求平面参数的GPU实现
终于有时间把这篇博客给补上了，理论知识我会在另外一片数学知识中讲到。
写了一个静态的方法，GPU实现的方便并不难（比起来DirectCompute里的复杂配置，amp的确提供了异常方面的接口）。
具体代码见下，我会做一些讲解。
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static void HoughFitPlanGPU(float* pXData, float* pYData, float* pZData, int count, PlanParameters& planParam) { concurrency::array_view<const float, 1> xdata(count, pXData); concurrency::array_view<const float, 1> ydata(count, pYData); concurrency::array_view<const float, 1> zdata(count, pZData); float miminor = 0.08f; int aN = planParam.aN, bN = planParam.bN, cN = planParam.cN, dN = planParam.dN; // for the special demand float* aParam = new float[aN]; CreateParam(aParam, aN, -PI_FIT/4.0f, PI_FIT/4.0f); float* bParam = new float[bN]; CreateParam(bParam, bN, -PI_FIT/4.0f, PI_FIT/4.0f); //std::vector<float> aParam(aN, 1.0); //CreateParam(aParam, aN, -PI_FIT/4.0f, PI_FIT/4.0f); //std::vector<float> bParam(bN, 0.5); //CreateParam(bParam, bN, -PI_FIT/4.0f, PI_FIT/4.0f); float* dParam = new float[dN]; for ( int i = 0; i < dN; i++) dParam[i] = (float)(i-13); concurrency::array_view<float,1> vaParam(aN, aParam); concurrency::array_view<float,1> vbParam(bN, bParam); concurrency::array_view<float,1> vdParam(dN, dParam); std::vector<float> voteRes( aN*bN*dN, 0); concurrency::array_view<float, 3> voteData(aN,bN,dN,voteRes); // 特别注意，不能是int型，否则会把shader设置成为int还是怎么，影响到参数空间的值dParam也会变成int值 voteData.discard_data(); concurrency::parallel_for_each( voteData.extent, [=](concurrency::index<3> idx) restrict(amp) { float a = vaParam(idx[0]); float b = vbParam(idx[1]); float c = 1.0f; float d = vdParam[idx[2]]; voteData[idx] = 0; for ( int m = 0; m < count; m++) { float value = a * xdata[m] + b * ydata[m] + zdata[m] + d; value = (value > 0)? value: -value; if(value < miminor) //voteData[idx] += d; voteData[idx]++; } } ); float max = 0; for ( int i = 0; i < aN; i++) { for ( int j = 0; j< bN; j++) { for (int k = 0; k < dN; k++) { if(voteData(i,j,k) > max) { max = voteData(i,j,k); planParam.a = aParam[i]; planParam.b = bParam[j]; planParam.c = 1.0f; planParam.d = dParam[k]; } } } } max = max; std::cout << max << std::endl; }
在C++ AMP中主要有array和array_view这两种数据容器。这两者主要的区别在于array类型的数据在创建时会在GPU显存上拥有一个备份，在GPU对该数据进行完运算之后，开发者必须手动将数据拷贝回CPU。与之相比，array_view其实是一个数据结构的封装，只有在它指向的数据被GPU调用时才会被拷贝到GPU上进行相应的计算。从下例中我们看到，声明array_view数据时需要提供两个模板参数：array_view元素的类型和数据结构的纬度。因为pXData，pYData和pZData都是一维数组，因此我们在声明时传入const float和1两个参数。其他所遇到的情况以此类推即可。【说明摘自程序员杂志第四期】
参数空间的设计可以根据自己的需求而定，因为在我的试验里，发现在z轴上的分布为40 - 60cm，所以我考虑将z的参数定为单位值，参数空间为a、b、d（点到平面的距离），a、b为-1到1的等差采样，采样率可以根据精度需求进行手动指定（优化选择当然更好，如果要把这个功能集成到现在的项目里可以会考虑做这一步）。
为了和GPU进行检查和对比，实现了CPU进行平面检测，在鉴定GPU效果良好后，对其进行改进，采用了迭代的方法提高检测进度。
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static void HoughFitPlanCPU(float* pXData, float* pYData, float* pZData, int count, PlanParameters& planParam)
{
float miminor = 0.01f;
int aN = planParam.aN, bN = planParam.bN, cN = planParam.cN, dN = planParam.dN;
// for the special demand
float band = 2.0f;
int iter = 6;
float* aParam = new float[aN];
float* bParam = new float[bN];
float* dParam = new float[dN];
for ( int i = 0; i < dN; i++)
dParam[i] = (float)(i-13);
while ( iter-- >0)
{
band = band / 2.0f;
CreateParam(aParam, aN, planParam.a - band, planParam.a + band);
CreateParam(bParam, bN, planParam.b - band, planParam.b + band);
//std::ofstream outfile("data3.txt");
float miniset = 10000.0f, dx, dy, dz;
std::vector<float> voteRes( aN*bN*dN, 0);
//int*** vote = new int**[dN];
for ( int i = 0; i < aN; i++)
{
//vote[i] = new int*[bN];
for ( int j = 0; j < bN; j++)
{
//vote[i][j] = new int[dN];
for (int k = 0; k < dN; k++)
{
long idx = i*bN*dN + j*dN + k;
float a = aParam[i];
float b = bParam[j];
float c = 1.0f;
float d = dParam[k];
float normal = (a*a + b*b + c*c + d*d);
//vote[i][j][k] = 0;
voteRes[idx] = 0;
for (int m = 0; m < count; m++)
{
float x = pXData[m], y = pYData[m], z = pZData[m];
float value = a*x + b*y + c*z + d;
value = (value >0)?value:(-value);
//value = value*value / 10000.0f;// / (x*x + y*y + z*z)/ normal;
if( value < miminor)
//voteRes[idx] += d;
voteRes[idx]++;
//vote[i][j][k]++;
}
//outfile << vote[i][j][k] <<"\t";
}
//outfile << std::endl;
}
}
//outfile.close();
float max = -0.01;
for ( int i = 0; i < aN; i++)
{
for ( int j = 0; j < bN; j++)
{
for (int k = 0; k < dN; k++)
{
long idx = i*bN*dN + j*dN + k;
if ( voteRes[idx] > max) //vote[i][j][k] > max)
{
max = voteRes[idx]; //vote[i][j][k];
planParam.a = aParam[i];
planParam.b = bParam[j];
planParam.d = dParam[k];
}
}
}
}
std::cout << max << std::endl;
}
}
测试代码
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int _tmain(int argc, _TCHAR* argv[])
{
// 0.457x + 0.787y + z - 9 = 0;
int count = 80, rand_count = 10;
float* XData = new float[count];
float* YData = new float[count];
float* ZData = new float[count];
for ( int i = 0; i<rand_count; i++)
{
ZData[count-1-i] = (float)rand()/1000.0f;
XData[count-1-i] = (float)rand()/1000.0f;
YData[count-1-i] = (float)rand()/1000.0f;
}
for ( int i = 0; i < count-rand_count; i++)
{
ZData[i] = (float)(i+20);
XData[i] = (float)(i*i)/100.0f;
YData[i] = (9.0f - ZData[i] - 0.457f*XData[i] ) / 0.787f;
}
PlanParameters planParam;
planParam.c = 1.0f;
planParam.cN = 1;
planParam.aN = 500;
planParam.bN = 500;
CFitLib::HoughFitPlanGPU(XData, YData, ZData,count, planParam);
std::cout << "GPU:" << planParam.aN << "\t" <<planParam.bN<< "\t" <<planParam.dN << std::endl;
std::cout << planParam.a << "\t" << planParam.b << "\t" << planParam.c << "\t" << planParam.d << std::endl;
planParam.a = 0.0f;
planParam.b = 0.0f;
planParam.aN = 100;
planParam.bN = 100;
CFitLib::HoughFitPlanCPU(XData, YData, ZData, count, planParam);
std::cout << "CPU:" << planParam.aN << "\t" <<planParam.bN<< "\t" <<planParam.dN << std::endl;
std::cout << planParam.a << "\t" << planParam.b << "\t" << planParam.c << "\t" << planParam.d << std::endl;
std::cout << (0.061*178 + 7.41)*0.65 <<std::endl;
system("pause");
return 0;
}
CPU递归迭代能找到更好的逼近结果，可考虑换成GPU进行迭代在降低算法复杂度。
【由于这段时间太多，写得很粗糙，请多多见谅】
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