DCF Tracker outCorrelationResponses Issue

Issue Overview

Users are experiencing difficulties with the DCF (Discriminative Correlation Filter) tracker example in the VPI (Vision Programming Interface). Specifically, the problem revolves around the inability to retrieve data from the outMaxCorrelationResponses parameter when using the vpiSubmitDCFTrackerLocalizeBatch function. The function consistently produces a value of 0, which is unexpected and prevents proper tracking functionality.

Possible Causes

1. Incorrect implementation: The user’s code might not be correctly implementing the VPI DCF tracker functionality, leading to unexpected results.

2. Version incompatibility: There could be a mismatch between the VPI library version and the code being used.

3. Backend issues: The problem might be specific to the chosen backend (CUDA or PVA), causing the correlation responses to be incorrectly calculated or retrieved.

4. Memory allocation problems: Insufficient or incorrect memory allocation for the outMaxCorrelationResponses array could lead to improper data retrieval.

5. Synchronization issues: The stream synchronization might not be occurring at the right time, causing the data to be accessed before it’s fully processed.

Troubleshooting Steps, Solutions & Fixes

1. Verify sample code execution:

   • Run the default sample provided by VPI to check if the issue persists:

     ./vpi_sample_19_dcf_tracker cuda ../assets/pedestrians.mp4 ../assets/pedestrians_bboxes.txt
     

   • If the sample works correctly, compare your implementation with the sample code to identify discrepancies.

2. Check outMaxCorrelationResponses initialization and usage:

   • Ensure that the outMaxCorrelationResponses array is properly created and initialized:

     CHECK_STATUS(vpiArrayCreate(maxTrackedTargets, VPI_ARRAY_TYPE_F32, 0, &outMaxCorrelationResponses));
     

   • Verify that the array is correctly passed to the vpiSubmitDCFTrackerLocalizeBatch function:

     CHECK_STATUS(vpiSubmitDCFTrackerLocalizeBatch(stream, 0, dcf, NULL, 0,
                                                   NULL,
                                                   tgtPatches, inTargets, outTargets,
                                                   NULL,
                                                   outMaxCorrelationResponses,
                                                   NULL));
     

3. Implement proper data retrieval:

   • After calling vpiSubmitDCFTrackerLocalizeBatch, use vpiArrayLockData to access the correlation response data:

     VPIArrayData outMaxCorrelationResponsesData;
     CHECK_STATUS(vpiArrayLockData(outMaxCorrelationResponses, VPI_LOCK_READ, VPI_ARRAY_BUFFER_HOST_AOS, &outMaxCorrelationResponsesData));
     auto *pCorValues = reinterpret_cast<float *>(outMaxCorrelationResponsesData.buffer.aos.data);
     // Process pCorValues here
     CHECK_STATUS(vpiArrayUnlock(outMaxCorrelationResponses));
     

4. Ensure proper stream synchronization:

   • Add a stream synchronization call before accessing the data:

     CHECK_STATUS(vpiStreamSync(stream));
     

5. Debug with print statements:

   • Add print statements to verify the values of outMaxCorrelationResponses at different stages of the process.

6. Check VPI version compatibility:

   • Ensure that you’re using the latest version of the VPI library compatible with your NVIDIA Jetson device.

7. Verify backend selection:

   • Test the code with both CUDA and PVA backends to see if the issue is backend-specific.

8. Review error handling:

   • Implement comprehensive error checking for all VPI function calls to catch any potential issues:

     #define CHECK_STATUS(STMT)                                    \
         do                                                        \
         {                                                         \
             VPIStatus status = (STMT);                            \
             if (status != VPI_SUCCESS)                            \
             {                                                     \
                 char buffer[VPI_MAX_STATUS_MESSAGE_LENGTH];       \
                 vpiGetLastStatusMessage(buffer, sizeof(buffer));  \
                 std::ostringstream ss;                            \
                 ss << vpiStatusGetName(status) << ": " << buffer; \
                 throw std::runtime_error(ss.str());               \
             }                                                     \
         } while (0);
     

9. Consult NVIDIA documentation:

   • Review the official NVIDIA VPI documentation for any known issues or additional configuration requirements for the DCF tracker.

If the issue persists after trying these solutions, consider reaching out to NVIDIA developer support or posting a detailed description of your problem, including your complete code and the steps to reproduce the issue, on the NVIDIA Developer Forums.