imaqFindTransformPattern incorrect return value

[Pacsoft]

Hi,

I am using function imaqFindTransformPattern() to setup a coordinate system. This function is returning a 0, and when I use function imaqGetLastError(), I get a "No error" string. My point is that my code is working properly so I do not know why imaqFindTransformPattern() returns a 0. The help file says that on success, a non-zero value should be returned. Any ideas ? Thanks.

[Scott_R]

Hello,

An error code of 0 indicates that no error has occurred.  There is an error in that documentation.  If you look at the list of error codes, linked from the documentation for imaqGetLastError(), a value of 0 indicates that no error has occurred.  Thank you for bringing this discrepancy to our attention.

Regards,

Scott R.

Applications Engineer

National Instruments

[Pacsoft]

The problem is that all functions returns 0 on failure, and they are actually doing it. In fact, the return value of the function is not the error code. Error codes are obtained via imaqGetLastError(). I think is not a problem with documentation, because so far that is the only function I have found is returning a 0 on success, instead of a non-zero. The problem is with the actual code.

[Scott_R]

Hello,

My understanding is that your code is functioning properly, but the functions are all returning 0 values.  In the documentation, it is stated that a return value of 0 corresponds to an error.  However, attempting to determine the error type generates a message which indicates that no error has occurred. 

Is that accurate?  I will investigate those functions and determine what value should be returned.  I will let you know when I find out if the problem is with the code or with the documentation.  Have you tried to force an error in your code to determine if a non-zero value is returned in that case?

Regards,
Scott R.
Applications Engineer
National Instruments

[Pacsoft]

The only function I have found up to now returning a 0 on success, is imaqFindTransformPattern(). Then I use imaqGetLastError(), and it returns "No Error". All other functions I am using return non-zero values on success, which is what I expect.

And yes, I have forced errors in the code. As I mentioned before, only imaqFindTransformPattern() returns 0 both on success and on failure. That is weird.

[Scott_R]

Hello,

How did you force the error?  Could you please attach an example of code that demonstrates the behavior that you have described? 

Regards,

Scott R.

Applications Engineer

National Instruments

[Pacsoft]

Hi,

This is an example of the code I am running. GrayscaleImage is an IMAQ_IMAGE_U8 image. CoordinateSystemPatternImage is an IMAQ_IMAGE_U8 image used as the reference for the coordinate system. AppFindTransformPatternOptions consists of the following:

   AppFindTransformPatternOptions.matchMode = IMAQ_MATCH_ROTATION_INVARIANT;  // Look for rotated images
   AppFindTransformPatternOptions.minMatchScore = MIN_SCORE; // 500
   AppFindTransformPatternOptions.subpixelAccuracy = TRUE;
   AppFindTransformPatternOptions.angleRanges = &Angles; // I set it from -45 to 45 degrees
   AppFindTransformPatternOptions.numRanges = 1;
   AppFindTransformPatternOptions.showSearchArea = FALSE;   
   AppFindTransformPatternOptions.showFeatureFound = TRUE;
   AppFindTransformPatternOptions.showResult = TRUE;

    if ((imaqFindTransformPattern(GrayscaleImage, CoordinateSystemPatternImage, &CoordSystem, IMAQ_NO_ROTATED_RECT, IMAQ_UPDATE_TRANSFORM, &AppFindTransformPatternOptions, NULL)) == 0){
     Error = imaqGetLastError();
     ErrorString = imaqGetErrorText(Error);
     if (Error)
      MessagePopup("Error", ErrorString);
     imaqDispose(ErrorString);
    }

On success, this function returns 0. That IS NOT what the documentation says. However, the function is doing what is supposed to.