Question for Hough space definition

Dear all:

After looking at the demo code on VLIB, it seems tell us some ideas from code segments below:

===========================================================

extern short TableSineBK_Minus80toPlus80resZeroPointSix_Q8[267];

extern short TableCosineBK_Minus80toPlus80resZeroPointSix_Q8[267];

extern unsigned short pEdgeMapList[2*30];

#define W 100

#define H 60

unsigned short calculatedOutHoughSpace[267*267];

unsigned short ping[267];

unsigned short pong[267];

unsigned short pang[267];

unsigned short peng[267];

void main( )

{

        //Creating input image

    int i;

        unsigned short x,y;

        unsigned char Im[W*H];

        unsigned int listsize[1];

    int maxRho, maxTheta,maxVal,maxIndex;

   //generating input image

   memset(Im,0,W*H);

   for(i=0;i<30;i++)

   {

           x=i+3;

           y=x*2+10;

           Im[x+y*W]=1;

   }

   //Convert the binary image to Edge list

   wrap_binarymatrix2index(Im,W,H,pEdgeMapList,listsize);

   //Hough space voting memset(calculatedOutHoughSpace,0,267*267);

        VLIB_houghLineFromList(

                pEdgeMapList,

                calculatedOutHoughSpace,

                W, // outBlkWidth             

                H, // outBlkHeight            

                                30,   // listSize

                267, // thetaRange,

                267, // rhoMaxLength

                                TableSineBK_Minus80toPlus80resZeroPointSix_Q8,

                           TableCosineBK_Minus80toPlus80resZeroPointSix_Q8,

                           ping,

                           pong,

                           pang,

                           peng );

    //Finding max

        maxVal=0;

        for(i=0;i<267*267;i++)

        {

                if(calculatedOutHoughSpace[i]>maxVal)

                {

                maxVal= calculatedOutHoughSpace[i];

                maxIndex = i;

                }

        }

        maxRho   = maxIndex%267;

        maxTheta = maxIndex/267;

        draw_line(Im,W,H,maxRho,maxTheta,TableSineBK_Minus80toPlus80resZeroPointSix_Q8,TableCosineBK_Minus80toPlus80resZeroPointSix_Q8);

void draw_line

(

unsigned char * Im,

unsigned short W,

unsigned short H,

short rho,

short theta,

const signed short *pSIN,

const signed short *pCOS

)

{                                                                     

    int x,y;

        short a,b;

        int r1;

        short rho1;

  signed int normLength;

  signed int diameter;      

  diameter = SQRTof2_Q8*max(W,H);

  normLength = 267 << 16;

  normLength /= diameter;  

  normLength /= 2;              

        a=pCOS[theta];

    b=pSIN[theta];

    for(y = 0; y<H; y++)

    {

            for(x = 0; x<W; x++)

        {   

                 r1=x*a+y*b;

             rho1 = (unsigned short) (((r1+diameter) * normLength + 32768) >> 16); //unwarping the parameter rho                                

                 if (abs(rho1-rho) <1)

                  Im[x+y*W]=1;

         }        

    }            

What we though are:

(1) maxRho = maxIndex%267; and maxTheta = maxIndex/267; so the coordinate for hough space is ρ(horizontal axis) /θ(vertical axis).

(2) ρ>0 and -80°<θ<80°, which both mapping to ρ[0:267] and θ[0:267].

(3)According to draw_line, we get one distance value for each angle value, but we can not understand the code segment below, can anyone reply the question?

=====================================

  diameter = SQRTof2_Q8*max(W,H);

  normLength = 267 << 16; ????

  normLength /= diameter; ????

  normLength /= 2;       ????   

…..

  rho1 = (unsigned short) (((r1+diameter) * normLength + 32768) >> 16); //unwarping the parameter rho  ????

Regards,

Alan