Image Processing and the ARToolkit

Example: Paddle Interaction
Proximity based
When two markers are within a certain distance of each other there is an interaction between the virtual objects. The paddle may "pick up" a virtual object or "push" it.

Tilting
At a certain angle, a virtual object can be made to "slide off" the paddle.

Shaking
A shaking motion can be used to delete an object.

Hitting
Objects can be removed by hitting them with the paddle

Local vs. Global Interactions
Local
Actions are determined by a single camera to marker transform - shaking, appearance, relative position, range.

Global
Actions determined from two relationships - marker to camera, and camera to world coordinates. The marker transform is determined in world coordinates to identify tilit, absolute position, obsolute rotation, hitting.

So all interactions are found based on the camera to marker transforms that are returned by the function arGetTransMat, which returns a 3 x 4 matrix that is the usual 4 x 4 3D transformation without the bottom row.

/* get the camera transformation */
arGetTransMat(&marker_info[k], marker_center, marker_width, marker_trans);

So the range from the camera to the marker is:

/* find the range */
Xpos = marker_trans[0][3];
Ypos = marker_trans[1][3];
Zpos = marker_trans[2][3];
range = sqrt(Xpos*Xpos+Ypos*Ypos+Zpos*Zpos);

# posted by Paul Mason @ 6:52 AM 0 comments

   f  s  x  0
   0 af  y  0
   0  0  1  0

# posted by Paul Mason @ 2:55 PM 0 comments

Read through this file and notice how it relates to the six steps of the application structure given in the previous post.

/*****************************************************************************/
// modified by Thomas Pintaric, Vienna University of Technology

#ifdef _WIN32
char         *vconf = "flipV,showDlg"; // see video.h for a list of supported parameters
#else
char         *vconf = "";
#endif
/*****************************************************************************/

int   xsize, ysize;
int   thresh = 100;
int   count = 0;

char    *cparam_name = "Data/camera_para.dat";
ARParam  cparam;

char    *patt_name = "Data/patt.hiro";
int      patt_id;
double   patt_width = 80.0;
double   patt_center[2] = {0.0, 0.0};
double   patt_trans[3][4];

static void init(void);
static void cleanup(void);
static void keyEvent( unsigned char key, int x, int y);
static void mainLoop(void);
static void draw( void );

int main(int argc, char **argv)
{
   init();

   arVideoCapStart();
   argMainLoop( NULL, keyEvent, mainLoop );
   return (0);
}

static void keyEvent( unsigned char key, int x, int y)
{
   /* quit if the ESC key is pressed */
   if( key == 0x1b ) {
      printf("*** %f (frame/sec)\n", (double)count/arUtilTimer());
      cleanup();
      exit(0);
   }
}

/* main loop */
static void mainLoop(void)
{
   ARUint8      *dataPtr;
   ARMarkerInfo *marker_info;
   int           marker_num;
   int           j, k;

   /* grab a video frame */
   if( (dataPtr = (ARUint8 *)arVideoGetImage()) == NULL ) {
      arUtilSleep(2);
      return;
   }
   if( count == 0 ) arUtilTimerReset();
   count++;

   argDrawMode2D();
   argDispImage( dataPtr, 0,0 );

   /* detect the markers in the video frame */
   if( arDetectMarker(dataPtr, thresh, &marker_info, &marker_num) < 0)
      cleanup();
      exit(0);
   }

   /* check for object visibility */
   k = -1;
   for( j = 0; j < marker_num; j++) {
      if( patt_id == marker_info[j].id ) {
         if( k == -1 ) k = j;
         else if( marker_info[k].cf < marker_info[j].cf) k = j;
      }
   }

   if( k == -1 ) {
      argSwapBuffers();
      return;
   }

   /* get the transformation between the marker and the real camera */
   arGetTransMat(&marker_info[k], patt_center, patt_width, patt_trans);

   draw();

   argSwapBuffers();
}

/* initialize the video path, read in the marker and camera parameters,
 and setup the graphics window */
static void init( void )
{
   ARParam wparam;

   /* open the video path */
   if( arVideoOpen( vconf ) < 0) exit(0);
   /* find the size of the window */
   if( arVideoInqSize(&xsize, &ysize) < 0) exit(0);
   printf("Image size (x,y) = (%d,%d)\n", xsize, ysize);

   /* read and set the initial camera parameters */
   if( arParamLoad(cparam_name, 1, &wparam)  < 0) {
      printf("Camera parameter load error !!\n");
      exit(0);
   }
   arParamChangeSize( &wparam, xsize, ysize, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;cparam );
   arInitCparam( &cparam );
   printf("*** Camera Parameter ***\n");
   arParamDisp( &cparam );

   /* read the marker (pattern) file */
   if( (patt_id=arLoadPatt(patt_name)) < 0 ) {
      printf("pattern load error !!\n");
      exit(0);
   }

   /* open the graphics window */
   argInit( &cparam, 1.0, 0, 0, 0, 0 );
}

/* cleanup function called when program exits */
static void cleanup(void)
{
   arVideoCapStop();
   arVideoClose();
   argCleanup();
}

static void draw( void )
{
   double    gl_para[16];
   GLfloat   mat_ambient[]     = {0.0, 0.0, 1.0, 1.0};
   GLfloat   mat_flash[]       = {0.0, 0.0, 1.0, 1.0};
   GLfloat   mat_flash_shiny[] = {50.0};
   GLfloat   light_position[]  = {100.0,-200.0,200.0,0.0};
   GLfloat   ambi[]            = {0.1, 0.1, 0.1, 0.1};
   GLfloat   lightZeroColor[]  = {0.9, 0.9, 0.9, 0.1};

   argDrawMode3D();
   argDraw3dCamera( 0, 0 );
   glClearDepth( 1.0 );
   glClear(GL_DEPTH_BUFFER_BIT);
   glEnable(GL_DEPTH_TEST);
   glDepthFunc(GL_LEQUAL);

   /* load the camera transformation matrix */
   argConvGlpara(patt_trans, gl_para);
   glMatrixMode(GL_MODELVIEW);
   glLoadMatrixd( gl_para );

   glEnable(GL_LIGHTING);
   glEnable(GL_LIGHT0);
   glLightfv(GL_LIGHT0, GL_POSITION, light_position);
   glLightfv(GL_LIGHT0, GL_AMBIENT, ambi);
   glLightfv(GL_LIGHT0, GL_DIFFUSE, lightZeroColor);
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_flash);
   glMaterialfv(GL_FRONT, GL_SHININESS, mat_flash_shiny);
   glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
   glMatrixMode(GL_MODELVIEW);
   glTranslatef( 0.0, 0.0, 25.0 );
   glutSolidCube(50.0);
   glDisable( GL_LIGHTING );
glDisable( GL_DEPTH_TEST );
}

# posted by Paul Mason @ 11:43 AM 0 comments

1. libAR - tracking
2. libARgsub - image drawing
3. libARvideo - video capturing

Application Structure

An ARToolkit application involves the following steps:

1. Initialize – start video, read marker patterns & camera parameters.

2. Grab video frame.
3. Detect markers & recognize patterns.
4. Calculate camera transformation relative to the detected patterns.
5. Draw virtual objects on detected patterns.

6. Close video.

Steps 2 through 5 are repeated continuously until the application quits, while steps 1 and 6 are done on initialization and shutdown respectively. In addition to these steps the application may need to respond to mouse, keyboard or other application specific events.

# posted by Paul Mason @ 9:01 AM 0 comments

• Microsoft Visual Studio .NET 2003 or Visual Studio 6.
• DSVideoLib-0.0.4-win32. Download from http://sf.net/projects/artoolkit
• GLUT. Download from http://www.opengl.org/resources/libraries/glut.html
• DirectX 9.0b or later SDK. If you are using VS6, you must use 9.0b as DirectX 9.0c no longer includes support for VS6. Download from http://msdn.microsoft.com/library/default.asp?url=/downloads/list/directx.asp
• (DirectX 9.0c October 2004 or later only) DirectX SDK Extras package. Once downloaded and unzipped, move the "Samples" folder into the top-level of the installed SDK path.
• (Optional, for VRML renderer only) OpenVRML-0.14.3-win32. Downloadfrom http://sf.net/projects/artoolkit.

1. Unpack the ARToolKit zip to a convenient location. This location will be referred to below as {ARToolKit}.
2. Unpack the DSVideoLib zip into {ARToolKit}.
3. Copy the files DSVideoLib.dll and DSVideoLibd.dll from{ARToolKit}\DSVideoLib\bin.vc70 into {ARToolKit}\bin.
4. Run the script {ARToolKit}\DSVideoLib\bin.vc70\register_filter.bat.
5. Install the GLUT DLL into the Windows System32 folder, and the library and headers into the VS platform SDK folders.
6. Run the script {ARToolKit}\Configure.win32.bat to create include/AR/config.h.
7. Open the ARToolKit.sln file (VS.NET) or ARToolkit.dsw file (VS6).
8. Open the Visual Studio search paths settings(Tools->Options->Directories for VS6, or Tools->Options->Projects->VC++Directories for VS.NET) and add the DirectX SDK Includes\ path and theDirectX Samples\C++\DirectShow\BaseClasses\ path to the top of the search path for headers, and the DirectX SDK Lib\ path to the top of thesearch path for libraries.
9. (Optional, only if rebuilding DSVideoLib). Build the DirectShow baseclasses strmbase.lib and strmbasd.lib. (More information can be found atThomas Pintarics homepage for DSVideoLib(http://www.ims.tuwien.ac.at/~thomas/dsvideolib.php)).
10. Build the toolkit.The VRML renderering library and example (libARvrml & simpleVRML) are optional builds:
11. Unpack the OpenVRML zip into {ARToolKit}.
12. Copy js32.dll from {ARToolKit}\OpenVRML\bin into {ARToolKit}\bin.
13. Enable the libARvrml and simpleVRML projects in the VS configuration manager and build.

# posted by Paul Mason @ 6:35 AM 0 comments

Augmented Reality (AR) - 2: The use of transparent HMDs to overlay computer generated images onto the physical environment. Precisely calibrated, rapid head tracking is required to sustain the illusion (HITLab Washington).

Tangible AR Interfaces: Those in which each virtual object is registered to a physical object and the user interacts with virtual objects by manipulating the corresponding tangible objects. In the Tangible AR approach the physical objects and interactions are equally as important as the virtual imagery and provide a very intuitive way to interact with the AR interface (Billinghurst, Kato and Poupyrev).

# posted by Paul Mason @ 11:25 AM 0 comments