perception/path/camera/docs/usecase1_pathdetector.md

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# Copyright (c) 2019-2020 NVIDIA CORPORATION.  All rights reserved.

@page pathperception_usecase1_pathdetector Path Perception Workflow

@note SW Release Applicability: This tutorial is applicable to modules in **NVIDIA DRIVE Software** releases.

The following code snippet shows the general structure of a program that uses path detector to detect drive-able paths from a single camera. Note that error handling is left out for clarity.

Initialize PathNet default parameters and then the module:
```
dwPathNetParams pathNetParams{};
dwPathNet_initDefaultParams(&pathNetParams));
dwPathNet_initialize(&pathNetHandle, &pathNetParams, sdkHandle));
```

Initialize Path detector module from initialized PathNet handle without calibrated camera:
```
dwPathDetector_initializeFromPathNet(&pathDetectorHandle,
                                     pathNetHandle,
                                     cameraWidth,
                                     cameraHeight,
                                     cudaStream,
                                     sdkHandle);
```

Initialize Path detector module from initialized PathNet handle with calibrated camera:
```
dwPathDetector_initializeFromPathNet(&pathDetectorHandle,
                                     pathNetHandle,
                                     cameraWidth,
                                     cameraHeight,
                                     calibratedCameraHandle,
                                     tranformationMatrix,
                                     cudaStream,
                                     sdkHandle);
```

Initialize detector parameters (optional):
```
dwPathDetector_setTemporalSmoothFactor(temporalSmoothFactor, pathDetectorHandle);
dwRect roi = {...};
dwPathDetector_setDetectionROI(&roi, pathDetectorHandle);
dwStatus dwPathDetector_setComputeCenterRailFrom3D(computeCenterRailFrom3D, pathDetectorHandle);
```

Detect paths from a video sequence:
```
while(true)
{
    dwPathDetection paths{};
    dwPathDetector_processDeviceAsync(frame, pathDetectorHandle);
    dwPathDetector_interpretHost(pathDetectorHandle);
    dwPathDetector_getPathDetections(&paths, pathDetectorHandle);
}
```

When finished, release the module handles:
```
dwPathDetector_release(pathDetectorHandle);
dwPathNet_release(pathNetHandle);
```

For more detailed workflow, please refer to the path detection sample: @ref dwx_path_perception_sample