C- 在一维字节数组中索引 x,y,z 坐标 [英] C- Indexing x,y,z coordinates in a 1D byte array

问题描述

我想评估曲面的值以实现行进四面体算法，但我不明白如何处理 .raw 无格式数据.

I want to evaluate the values of the surface to implement a marching tetrahedron algorithm, but I don't understand how to work with .raw unformatted data.

在将带有卷数据集的 .raw 文件加载到一维字节数组中后，应该应用什么算术变换来从中获取与 X、Y、Z 关联的值?这是我知道加载 .raw 文件的唯一方法，我可以创建一个 3D 字节数组而不是这个吗?如何?

After loading a .raw file with a volume dataset into a 1D byte array, what arithmetic transformation should be applied to get the value associated to X,Y,Z from it? This is the only way I know to load .raw files, could I create a 3D byte array instead of this? How?

int XDIM=256, YDIM=256, ZDIM=256;
const int size = XDIM*YDIM*ZDIM;
bool LoadVolumeFromFile(const char* fileName) {

    FILE *pFile = fopen(fileName,"rb");
   if(NULL == pFile) {
    return false;
   }

   GLubyte* pVolume=new GLubyte[size]; //<- here pVolume is a 1D byte array 
   fread(pVolume,sizeof(GLubyte),size,pFile);
   fclose(pFile);

推荐答案

在 (x, y, z) 处索引基准的方式是:

The way you'd index the datum at (x, y, z) is:

pVolume[((x * 256) + y) * 256 + z]

在幕后，如果您编写，这就是 C 编译器为您所做的:

Behind the scenes, this is what the C compiler does for you if you write:

GLuByte array[256][256][256];

array[x][y][z]

仅仅因为 C 索引从 0 开始，它才起作用；如果语言从 1 开始索引，则必须修改计算以实现在进行索引之前通过从 x、y 和 z 中的每一个中减去一个而获得的净结果.

It only works that simply because C indexes from 0; if the language indexed from 1, you'd have to revise the calculation to achieve the net result obtained by subtracting one from each of x, y and z before doing the indexing.

你能概括任意维度的公式吗?

Can you generalize the formula for arbitrary dimensions?

给定(数值并不重要):

Given (where the numeric values don't really matter):

DIMx = 256
DIMy = 128
DIMz =  64

一维数组 pData 中 (x, y, z) 处的数据位于:

the datum at (x, y, z) in 1D array pData is found at:

pData[((x * DIMx) + y) * DIMy + z]

DIMz 的值主要用于验证:0 <= z <DIMz(使用数学而不是 C 表示法)，并且并行 0 <= x <暗淡;0 <= y <= DIMy.z 的 C 表示法是 0 <= z &&z＜DIMz;对 x 和 y 重复 mutatis mutandis.

The value of DIMz serves primarily for validation: 0 <= z < DIMz (using mathematical rather than C notation), and in parallel 0 <= x < DIMx; 0 <= y <= DIMy. The C notation for z is 0 <= z && z < DIMz; repeat mutatis mutandis for x and y.

这篇关于C- 在一维字节数组中索引 x,y,z 坐标的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！