Geometric Template Matching in LabVIEW

In NI's IMAQ Vision Concepts Manual, geometric template matching is described as follows. Geometric matching locates regions in a grayscale image that match a model, or template, of a reference pattern. Geometric matching is specialized to locate templates that are characterized by distinct geometric or shape information. When using geometric matching, a template is created that represents the object to be searched. Machine vision application then searches for instances of the template in each inspection image and calculates a score for each match. The score relates how closely the template resembles the located matches. Geometric matching finds template matches regardless of lighting variation, blur, noise, occlusion, and geometric transformations such as shifting, rotation, or scaling of the template.
The VIs such as IMAQ Find CoordSys (Pattern) 2 are used to locate the model. The template for the model is created as discussed in the following steps.

Open Template Editor in Windows by clicking Start -> All Programs -> National Instruments -> Vision -> Template Editor. Click File menu->New Template.... Select Geometric Matching Template (Edge Based) and browse an image to extract the template from. In the Select Template Region tab, define a region. For example, start at (200,300) and drag the mouse cursor to (232,332) and release it. Then, you can move the selection to the desired location. In the Define curves tab, specify curve parameters, e.g., Extraction mode to normal, Edge Threshold to 32, Edge Filter size to Fine, Minimum Length to 5, Row Search Step Size to 1 and Column Search Step size to 1. The setting in Customize Scoring and Specify Match Options tabs are set as default. Save the template by clicking File -> Save Template....

As an example, I have created a few VIs at the following link.

Geometric Template Matching on GitHub

Initialization for the VI inputs is shown below.

Byte Stuffing

I occasionally need to write programs to send and receive data bytes from one device to another. That is why I arbitrarily choose a simple variant of byte stuffing methods to build frames to send and receive data. To delimit the frame, control characters - 0x02 and 0x03- are defined as start of text (STX) and end of text (ETX) respectively. For error detection, exclusive-or of data bytes is appended after the ETX as a checksum. If you need better error detection, CRC as described at

CRC Calculation in VB and C

can also be used.

For example, if we want to send two bytes of data -

0x30 0x31,

the resulting frame will be

0x02 0x30 0x31 0x03 0x01

,where 0x02 at the start is added as STX, followed by data bytes and the byte before the last one, 0x03, is added as ETX. Since the exclusive-or of data bytes, 0x02^0x03, is 0x01, it is appended at the end as checksum. How can we send data that contains 0x02 or 0x03 which were already used as control characters? We need to define another control character 0x10 as Data Link Escape (DLE) to mark data that are not control characters. As an another example, let us build a frame for five data bytes -

0x30 0x02 0x65 0x10 0x03.

We will do byte stuffing by putting DLE in front of every data byte that conflicts with STX, ETX, or DLE. And

0x02 0x30 0x10 0x02 0x65 0x10 0x10 0x10 0x03 0x03 0x44

will be the resulting frame. I have developed a few programs in C and LabVIEW. Example programs can be downloaded at the following links.

Byte Stuffing on GitHub


The following is the C++ code to build, send and receive a frame.

// Byte stuffing- sending and receiving frames
// Author: Yan Naing Aye

#ifndef  FRAME_H
#define FRAME_H

#include 
#define STX 0x02
#define ETX 0x03
#define DLE 0x10

#define TX_BUF_SIZE 128
#define RX_BUF_SIZE 128
enum RX_STATE { IGNORE,RECEIVING,ESCAPE,RXCRC1,RXCRC2 };
//-----------------------------------------------------------------------------
class Frame {    
    RX_STATE rState;
protected:
    int TxN;//number of transmitting bytes
    int RxN;//number of receiving bytes
    char tb[TX_BUF_SIZE];//transmit buffer
    char rb[RX_BUF_SIZE];//receiving data
public:
    Frame();
    int setTxFrame(char* d,int n);
    unsigned int CRC16CCITT_Calculate(char* s,unsigned char len,unsigned int crc);
    int getTxN();
    int getRxN();
    int receiveRxFrame(char c);//get receiving frame from received char
    char* getTxBuf();
    char* getRxBuf();
};
//-----------------------------------------------------------------------------
Frame::Frame():TxN(0),RxN(0),rState(IGNORE){}
//-----------------------------------------------------------------------------
char* Frame::getTxBuf(){
    return tb;
}
//-----------------------------------------------------------------------------
char* Frame::getRxBuf(){
    return rb;
}
//-----------------------------------------------------------------------------
//Prepare transmitting frame
int Frame::setTxFrame(char* d,int n)
{
    unsigned int txcrc=0xFFFF;//initialize crc
    char c;
    int i=0,j=0;
    tb[i++]=STX;//start of frame
    for(j=0;j < n;j++) {
        c=d[j];
        if((c==STX)||(c==ETX)||(c==DLE)) tb[i++]=(DLE);
        tb[i++]=c;
    }
    tb[i++]=(ETX);//end of frame

    txcrc=CRC16CCITT_Calculate(d,n,txcrc);//calculate crc
    tb[i++]=txcrc & 0xFF;
    tb[i++]=(txcrc >> 8) & 0xFF;
    TxN=i;
    return TxN;
}
//-----------------------------------------------------------------------------
//Inputs
//s : pointer to input char string
//len: string len (maximum 255)
//crc: initial CRC value

//Output
//Returns calculated CRC
unsigned int Frame::CRC16CCITT_Calculate(char* s,unsigned char len,unsigned int crc)
{
    //CRC Order: 16
    //CCITT(recommendation) : F(x)= x16 + x12 + x5 + 1
    //CRC Poly: 0x1021
    //Operational initial value:  0xFFFF
    //Final xor value: 0
    unsigned char i,j;
    for(i=0;i < len;i++,s++) {
        crc^=((unsigned int)(*s) & 0xFF) << 8;
        for(j=0;j<8;j++) {
            if(crc & 0x8000) crc=(crc << 1)^0x1021;
            else crc <<=1;
        }
    }
    return (crc & 0xFFFF);//truncate last 16 bit
}
//-----------------------------------------------------------------------------
//get number of transmitting bytes
int Frame::getTxN()
{
    return TxN;
}
//-----------------------------------------------------------------------------
//get number of transmitting bytes
int Frame::getRxN()
{
    return RxN;
}
//-----------------------------------------------------------------------------
//process receiving char
int Frame::receiveRxFrame(char c)
{
    static char b;
    unsigned int crc;
    unsigned int rxcrc=0xFFFF;//initialize CRC
    switch(rState){
        case IGNORE:
            if(c==STX) { rState=RECEIVING;RxN=0;}
            break;
        case RECEIVING:
            if(c==STX) { rState=RECEIVING;RxN=0;}
            else if(c==ETX){rState=RXCRC1;}
            else if(c==DLE){ rState=ESCAPE; }
            else { rb[RxN++]=c; }
            break;
        case ESCAPE:
            rb[RxN++]=c; rState=RECEIVING;
            break;
        case RXCRC1:
            b=c; rState=RXCRC2;
            break;
        case RXCRC2:
            rState=IGNORE;
            crc=( (int)c << 8 | ((int)b & 0xFF) ) & 0xFFFF;//get received crc
            rxcrc=CRC16CCITT_Calculate(rb,RxN,rxcrc);//calculate crc
            //printf("crc: %x  rxcrc:%x \n",crc,rxcrc);
            if(rxcrc==crc){return RxN;}//if crc is correct            
            else {RxN=0;}//discard the frame

            break;
    }
    return 0;
}

//-----------------------------------------------------------------------------

//#############################################################################

class Frame2:public Frame {
    char Dt[20];//transmitting data
public:
    Frame2();
    void printTxFrame();
    void printRxFrame();
    void printRxData();
    void setTxData(float x,float y,float z,float b,float t);
};
//-----------------------------------------------------------------------------
Frame2::Frame2():Frame(),Dt(""){}
//-----------------------------------------------------------------------------
//Print out frame content
void Frame2::printTxFrame()
{
    printf("Tx frame buffer: ");
    for(int j=0;j < TxN;j++) printf("%02X ",(unsigned char)tb[j]);
    printf("\n");
}
//-----------------------------------------------------------------------------
//Print out frame content
void Frame2::printRxFrame()
{
    printf("Rx data buffer: ");
    for(int j=0;j < RxN;j++) printf("%02X ",(unsigned char)rb[j]);
    printf("\n");
}
//-----------------------------------------------------------------------------
//Set transmitting data
void Frame2::setTxData(float x,float y,float z,float b,float t)
{
    *(float*)(Dt)=x;
    *(float*)(Dt+4)=y;
    *(float*)(Dt+8)=z;
    *(float*)(Dt+12)=b;
    *(float*)(Dt+16)=t;
    Frame::setTxFrame(Dt,20);
}
//-----------------------------------------------------------------------------
//Print out received data
void Frame2::printRxData()
{
    float x,y,z,b,t;
    x=*(float*)(Dt);
    y=*(float*)(Dt+4);
    z=*(float*)(Dt+8);
    b=*(float*)(Dt+12);
    t=*(float*)(Dt+16);
    printf("Rx data: %f %f %f %f %f \n",x,y,z,b,t);
}
//-----------------------------------------------------------------------------

#endif // FRAME_H