# Feature Detector

Example shows capabilities of
[FeatureTracker](https://docs.luxonis.com/software-v3/depthai/examples/feature_tracker/feature_tracker.md). It only detects
features. [Feature Tracker](https://docs.luxonis.com/software-v3/depthai/examples/feature_tracker/feature_tracker.md) example also
tracks these features.

## Demo

This example requires the DepthAI v3 API, see [installation instructions](https://docs.luxonis.com/software-v3/depthai.md).

## Source code

#### Python

```python
#!/usr/bin/env python3

import cv2
import depthai as dai

# Create pipeline
pipeline = dai.Pipeline()

# Define sources and outputs
monoLeft = pipeline.create(dai.node.MonoCamera)
monoRight = pipeline.create(dai.node.MonoCamera)
featureTrackerLeft = pipeline.create(dai.node.FeatureTracker)
featureTrackerRight = pipeline.create(dai.node.FeatureTracker)

xoutPassthroughFrameLeft = pipeline.create(dai.node.XLinkOut)
xoutTrackedFeaturesLeft = pipeline.create(dai.node.XLinkOut)
xoutPassthroughFrameRight = pipeline.create(dai.node.XLinkOut)
xoutTrackedFeaturesRight = pipeline.create(dai.node.XLinkOut)
xinTrackedFeaturesConfig = pipeline.create(dai.node.XLinkIn)

xoutPassthroughFrameLeft.setStreamName("passthroughFrameLeft")
xoutTrackedFeaturesLeft.setStreamName("trackedFeaturesLeft")
xoutPassthroughFrameRight.setStreamName("passthroughFrameRight")
xoutTrackedFeaturesRight.setStreamName("trackedFeaturesRight")
xinTrackedFeaturesConfig.setStreamName("trackedFeaturesConfig")

# Properties
monoLeft.setResolution(dai.MonoCameraProperties.SensorResolution.THE_400_P)
monoLeft.setCamera("left")
monoRight.setResolution(dai.MonoCameraProperties.SensorResolution.THE_400_P)
monoRight.setCamera("right")

# Disable optical flow
featureTrackerLeft.initialConfig.setMotionEstimator(False)
featureTrackerRight.initialConfig.setMotionEstimator(False)

# Linking
monoLeft.out.link(featureTrackerLeft.inputImage)
featureTrackerLeft.passthroughInputImage.link(xoutPassthroughFrameLeft.input)
featureTrackerLeft.outputFeatures.link(xoutTrackedFeaturesLeft.input)
xinTrackedFeaturesConfig.out.link(featureTrackerLeft.inputConfig)

monoRight.out.link(featureTrackerRight.inputImage)
featureTrackerRight.passthroughInputImage.link(xoutPassthroughFrameRight.input)
featureTrackerRight.outputFeatures.link(xoutTrackedFeaturesRight.input)
xinTrackedFeaturesConfig.out.link(featureTrackerRight.inputConfig)

featureTrackerConfig = featureTrackerRight.initialConfig.get()

print("Press 's' to switch between Harris and Shi-Thomasi corner detector!")

# Connect to device and start pipeline
with dai.Device(pipeline) as device:

    # Output queues used to receive the results
    passthroughImageLeftQueue = device.getOutputQueue("passthroughFrameLeft", 8, False)
    outputFeaturesLeftQueue = device.getOutputQueue("trackedFeaturesLeft", 8, False)
    passthroughImageRightQueue = device.getOutputQueue("passthroughFrameRight", 8, False)
    outputFeaturesRightQueue = device.getOutputQueue("trackedFeaturesRight", 8, False)

    inputFeatureTrackerConfigQueue = device.getInputQueue("trackedFeaturesConfig")

    leftWindowName = "left"
    rightWindowName = "right"

    def drawFeatures(frame, features):
        pointColor = (0, 0, 255)
        circleRadius = 2
        for feature in features:
            cv2.circle(frame, (int(feature.position.x), int(feature.position.y)), circleRadius, pointColor, -1, cv2.LINE_AA, 0)

    while True:
        inPassthroughFrameLeft = passthroughImageLeftQueue.get()
        passthroughFrameLeft = inPassthroughFrameLeft.getFrame()
        leftFrame = cv2.cvtColor(passthroughFrameLeft, cv2.COLOR_GRAY2BGR)

        inPassthroughFrameRight = passthroughImageRightQueue.get()
        passthroughFrameRight = inPassthroughFrameRight.getFrame()
        rightFrame = cv2.cvtColor(passthroughFrameRight, cv2.COLOR_GRAY2BGR)

        trackedFeaturesLeft = outputFeaturesLeftQueue.get().trackedFeatures
        drawFeatures(leftFrame, trackedFeaturesLeft)

        trackedFeaturesRight = outputFeaturesRightQueue.get().trackedFeatures
        drawFeatures(rightFrame, trackedFeaturesRight)

        # Show the frame
        cv2.imshow(leftWindowName, leftFrame)
        cv2.imshow(rightWindowName, rightFrame)

        key = cv2.waitKey(1)
        if key == ord('q'):
            break
        elif key == ord('s'):
            if featureTrackerConfig.cornerDetector.type == dai.FeatureTrackerConfig.CornerDetector.Type.HARRIS:
                featureTrackerConfig.cornerDetector.type = dai.FeatureTrackerConfig.CornerDetector.Type.SHI_THOMASI
                print("Switching to Shi-Thomasi")
            else:
                featureTrackerConfig.cornerDetector.type = dai.FeatureTrackerConfig.CornerDetector.Type.HARRIS
                print("Switching to Harris")

            cfg = dai.FeatureTrackerConfig()
            cfg.set(featureTrackerConfig)
            inputFeatureTrackerConfigQueue.send(cfg)
```

#### C++

```cpp
#include <iostream>

// Includes common necessary includes for development using depthai library
#include "depthai/depthai.hpp"
#include "deque"
#include "unordered_map"
#include "unordered_set"

static void drawFeatures(cv::Mat& frame, std::vector<dai::TrackedFeature>& features) {
    static const auto pointColor = cv::Scalar(0, 0, 255);
    static const int circleRadius = 2;
    for(auto& feature : features) {
        cv::circle(frame, cv::Point(feature.position.x, feature.position.y), circleRadius, pointColor, -1, cv::LINE_AA, 0);
    }
}

int main() {
    using namespace std;

    // Create pipeline
    dai::Pipeline pipeline;

    // Define sources and outputs
    auto monoLeft = pipeline.create<dai::node::MonoCamera>();
    auto monoRight = pipeline.create<dai::node::MonoCamera>();
    auto featureTrackerLeft = pipeline.create<dai::node::FeatureTracker>();
    auto featureTrackerRight = pipeline.create<dai::node::FeatureTracker>();

    auto xoutPassthroughFrameLeft = pipeline.create<dai::node::XLinkOut>();
    auto xoutTrackedFeaturesLeft = pipeline.create<dai::node::XLinkOut>();
    auto xoutPassthroughFrameRight = pipeline.create<dai::node::XLinkOut>();
    auto xoutTrackedFeaturesRight = pipeline.create<dai::node::XLinkOut>();
    auto xinTrackedFeaturesConfig = pipeline.create<dai::node::XLinkIn>();

    xoutPassthroughFrameLeft->setStreamName("passthroughFrameLeft");
    xoutTrackedFeaturesLeft->setStreamName("trackedFeaturesLeft");
    xoutPassthroughFrameRight->setStreamName("passthroughFrameRight");
    xoutTrackedFeaturesRight->setStreamName("trackedFeaturesRight");
    xinTrackedFeaturesConfig->setStreamName("trackedFeaturesConfig");

    // Properties
    monoLeft->setResolution(dai::MonoCameraProperties::SensorResolution::THE_720_P);
    monoLeft->setCamera("left");
    monoRight->setResolution(dai::MonoCameraProperties::SensorResolution::THE_720_P);
    monoRight->setCamera("right");

    // Disable optical flow
    featureTrackerLeft->initialConfig.setMotionEstimator(false);
    featureTrackerRight->initialConfig.setMotionEstimator(false);

    // Linking
    monoLeft->out.link(featureTrackerLeft->inputImage);
    featureTrackerLeft->passthroughInputImage.link(xoutPassthroughFrameLeft->input);
    featureTrackerLeft->outputFeatures.link(xoutTrackedFeaturesLeft->input);
    xinTrackedFeaturesConfig->out.link(featureTrackerLeft->inputConfig);

    monoRight->out.link(featureTrackerRight->inputImage);
    featureTrackerRight->passthroughInputImage.link(xoutPassthroughFrameRight->input);
    featureTrackerRight->outputFeatures.link(xoutTrackedFeaturesRight->input);
    xinTrackedFeaturesConfig->out.link(featureTrackerRight->inputConfig);

    auto featureTrackerConfig = featureTrackerRight->initialConfig.get();

    printf("Press 's' to switch between Harris and Shi-Thomasi corner detector! \n");

    // Connect to device and start pipeline
    dai::Device device(pipeline);

    // Output queues used to receive the results
    auto passthroughImageLeftQueue = device.getOutputQueue("passthroughFrameLeft", 8, false);
    auto outputFeaturesLeftQueue = device.getOutputQueue("trackedFeaturesLeft", 8, false);
    auto passthroughImageRightQueue = device.getOutputQueue("passthroughFrameRight", 8, false);
    auto outputFeaturesRightQueue = device.getOutputQueue("trackedFeaturesRight", 8, false);

    auto inputFeatureTrackerConfigQueue = device.getInputQueue("trackedFeaturesConfig");

    const auto leftWindowName = "left";
    const auto rightWindowName = "right";

    while(true) {
        auto inPassthroughFrameLeft = passthroughImageLeftQueue->get<dai::ImgFrame>();
        cv::Mat passthroughFrameLeft = inPassthroughFrameLeft->getFrame();
        cv::Mat leftFrame;
        cv::cvtColor(passthroughFrameLeft, leftFrame, cv::COLOR_GRAY2BGR);

        auto inPassthroughFrameRight = passthroughImageRightQueue->get<dai::ImgFrame>();
        cv::Mat passthroughFrameRight = inPassthroughFrameRight->getFrame();
        cv::Mat rightFrame;
        cv::cvtColor(passthroughFrameRight, rightFrame, cv::COLOR_GRAY2BGR);

        auto trackedFeaturesLeft = outputFeaturesLeftQueue->get<dai::TrackedFeatures>()->trackedFeatures;
        drawFeatures(leftFrame, trackedFeaturesLeft);

        auto trackedFeaturesRight = outputFeaturesRightQueue->get<dai::TrackedFeatures>()->trackedFeatures;
        drawFeatures(rightFrame, trackedFeaturesRight);

        // Show the frame
        cv::imshow(leftWindowName, leftFrame);
        cv::imshow(rightWindowName, rightFrame);

        int key = cv::waitKey(1);
        if(key == 'q') {
            break;
        } else if(key == 's') {
            if(featureTrackerConfig.cornerDetector.type == dai::FeatureTrackerConfig::CornerDetector::Type::HARRIS) {
                featureTrackerConfig.cornerDetector.type = dai::FeatureTrackerConfig::CornerDetector::Type::SHI_THOMASI;
                printf("Switching to Shi-Thomasi \n");
            } else {
                featureTrackerConfig.cornerDetector.type = dai::FeatureTrackerConfig::CornerDetector::Type::HARRIS;
                printf("Switching to Harris \n");
            }
            auto cfg = dai::FeatureTrackerConfig();
            cfg.set(featureTrackerConfig);
            inputFeatureTrackerConfigQueue->send(cfg);
        }
    }
    return 0;
}
```

## Pipeline

### examples/feature_detector.pipeline.json

```json
{
  "pipeline": {
    "connections": [
      {
        "node1Id": 0,
        "node1Output": "out",
        "node1OutputGroup": "",
        "node2Id": 2,
        "node2Input": "inputImage",
        "node2InputGroup": ""
      },
      {
        "node1Id": 8,
        "node1Output": "out",
        "node1OutputGroup": "",
        "node2Id": 2,
        "node2Input": "inputConfig",
        "node2InputGroup": ""
      },
      {
        "node1Id": 2,
        "node1Output": "passthroughInputImage",
        "node1OutputGroup": "",
        "node2Id": 4,
        "node2Input": "in",
        "node2InputGroup": ""
      },
      {
        "node1Id": 2,
        "node1Output": "outputFeatures",
        "node1OutputGroup": "",
        "node2Id": 5,
        "node2Input": "in",
        "node2InputGroup": ""
      },
      {
        "node1Id": 1,
        "node1Output": "out",
        "node1OutputGroup": "",
        "node2Id": 3,
        "node2Input": "inputImage",
        "node2InputGroup": ""
      },
      {
        "node1Id": 8,
        "node1Output": "out",
        "node1OutputGroup": "",
        "node2Id": 3,
        "node2Input": "inputConfig",
        "node2InputGroup": ""
      },
      {
        "node1Id": 3,
        "node1Output": "passthroughInputImage",
        "node1OutputGroup": "",
        "node2Id": 6,
        "node2Input": "in",
        "node2InputGroup": ""
      },
      {
        "node1Id": 3,
        "node1Output": "outputFeatures",
        "node1OutputGroup": "",
        "node2Id": 7,
        "node2Input": "in",
        "node2InputGroup": ""
      }
    ],
    "globalProperties": {
      "calibData": null,
      "cameraTuningBlobSize": null,
      "cameraTuningBlobUri": "",
      "leonCssFrequencyHz": 700000000.0,
      "leonMssFrequencyHz": 700000000.0,
      "pipelineName": null,
      "pipelineVersion": null,
      "sippBufferSize": 18432,
      "sippDmaBufferSize": 16384,
      "xlinkChunkSize": -1
    },
    "nodes": [
      [
        0,
        {
          "id": 0,
          "ioInfo": [
            [
              [
                "",
                "inputControl"
              ],
              {
                "blocking": true,
                "group": "",
                "id": 1,
                "name": "inputControl",
                "queueSize": 8,
                "type": 3,
                "waitForMessage": false
              }
            ],
            [
              [
                "",
                "out"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 2,
                "name": "out",
                "queueSize": 8,
                "type": 0,
                "waitForMessage": false
              }
            ],
            [
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                "raw"
              ],
              {
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                "name": "raw",
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            [
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              {
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                "name": "frameEvent",
                "queueSize": 8,
                "type": 0,
                "waitForMessage": false
              }
            ]
          ],
          "name": "MonoCamera",
          "properties": {
            "boardSocket": -1,
            "cameraName": "left",
            "fps": 30.0,
            "imageOrientation": -1,
            "initialControl": {
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              "aeMaxExposureTimeUs": 0,
              "aeRegion": {
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              },
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              "contrast": 0,
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              "expManual": {
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              },
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              "lensPosAutoInfinity": 0,
              "lensPosAutoMacro": 0,
              "lensPosition": 0,
              "lensPositionRaw": 0.0,
              "lowPowerNumFramesBurst": 0,
              "lowPowerNumFramesDiscard": 0,
              "lumaDenoise": 0,
              "saturation": 0,
              "sceneMode": 0,
              "sharpness": 0,
              "strobeConfig": {
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                "enable": 0,
                "gpioNumber": 0
              },
              "strobeTimings": {
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                "exposureEndOffsetUs": 0
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            "rawPacked": null,
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      [
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              {
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                "group": "",
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                "name": "inputControl",
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              }
            ],
            [
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                "",
                "out"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 6,
                "name": "out",
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                "type": 0,
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              }
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              ],
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                "name": "frameEvent",
                "queueSize": 8,
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          ],
          "name": "MonoCamera",
          "properties": {
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            "imageOrientation": -1,
            "initialControl": {
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              "aeMaxExposureTimeUs": 0,
              "aeRegion": {
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                "width": 0,
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              },
              "afRegion": {
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                "priority": 0,
                "width": 0,
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              },
              "antiBandingMode": 0,
              "autoFocusMode": 3,
              "awbLockMode": false,
              "awbMode": 0,
              "brightness": 0,
              "captureIntent": 0,
              "chromaDenoise": 0,
              "cmdMask": 0,
              "contrast": 0,
              "controlMode": 0,
              "effectMode": 0,
              "expCompensation": 0,
              "expManual": {
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                "frameDurationUs": 0,
                "sensitivityIso": 0
              },
              "frameSyncMode": 0,
              "lensPosAutoInfinity": 0,
              "lensPosAutoMacro": 0,
              "lensPosition": 0,
              "lensPositionRaw": 0.0,
              "lowPowerNumFramesBurst": 0,
              "lowPowerNumFramesDiscard": 0,
              "lumaDenoise": 0,
              "saturation": 0,
              "sceneMode": 0,
              "sharpness": 0,
              "strobeConfig": {
                "activeLevel": 0,
                "enable": 0,
                "gpioNumber": 0
              },
              "strobeTimings": {
                "durationUs": 0,
                "exposureBeginOffsetUs": 0,
                "exposureEndOffsetUs": 0
              },
              "wbColorTemp": 0
            },
            "isp3aFps": 0,
            "numFramesPool": 3,
            "numFramesPoolRaw": 3,
            "rawPacked": null,
            "resolution": 2
          }
        }
      ],
      [
        2,
        {
          "id": 2,
          "ioInfo": [
            [
              [
                "",
                "inputConfig"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 9,
                "name": "inputConfig",
                "queueSize": 4,
                "type": 3,
                "waitForMessage": false
              }
            ],
            [
              [
                "",
                "inputImage"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 10,
                "name": "inputImage",
                "queueSize": 4,
                "type": 3,
                "waitForMessage": true
              }
            ],
            [
              [
                "",
                "outputFeatures"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 11,
                "name": "outputFeatures",
                "queueSize": 8,
                "type": 0,
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              }
            ],
            [
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                "",
                "passthroughInputImage"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 12,
                "name": "passthroughInputImage",
                "queueSize": 8,
                "type": 0,
                "waitForMessage": false
              }
            ]
          ],
          "name": "FeatureTracker",
          "properties": {
            "initialConfig": {
              "cornerDetector": {
                "cellGridDimension": 4,
                "enableSobel": true,
                "enableSorting": true,
                "numMaxFeatures": 0,
                "numTargetFeatures": 320,
                "thresholds": {
                  "decreaseFactor": 0.8999999761581421,
                  "increaseFactor": 1.100000023841858,
                  "initialValue": 0.0,
                  "max": 0.0,
                  "min": 0.0
                },
                "type": 0
              },
              "featureMaintainer": {
                "enable": true,
                "lostFeatureErrorThreshold": 50000.0,
                "minimumDistanceBetweenFeatures": 50.0,
                "trackedFeatureThreshold": 200000.0
              },
              "motionEstimator": {
                "enable": false,
                "opticalFlow": {
                  "epsilon": 0.009999999776482582,
                  "maxIterations": 9,
                  "pyramidLevels": 0,
                  "searchWindowHeight": 5,
                  "searchWindowWidth": 5
                },
                "type": 0
              }
            },
            "numMemorySlices": 1,
            "numShaves": 1
          }
        }
      ],
      [
        3,
        {
          "id": 3,
          "ioInfo": [
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              [
                "",
                "inputConfig"
              ],
              {
                "blocking": false,
                "group": "",
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                "name": "inputConfig",
                "queueSize": 4,
                "type": 3,
                "waitForMessage": false
              }
            ],
            [
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                "inputImage"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 14,
                "name": "inputImage",
                "queueSize": 4,
                "type": 3,
                "waitForMessage": true
              }
            ],
            [
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                "",
                "outputFeatures"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 15,
                "name": "outputFeatures",
                "queueSize": 8,
                "type": 0,
                "waitForMessage": false
              }
            ],
            [
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                "",
                "passthroughInputImage"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 16,
                "name": "passthroughInputImage",
                "queueSize": 8,
                "type": 0,
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              }
            ]
          ],
          "name": "FeatureTracker",
          "properties": {
            "initialConfig": {
              "cornerDetector": {
                "cellGridDimension": 4,
                "enableSobel": true,
                "enableSorting": true,
                "numMaxFeatures": 0,
                "numTargetFeatures": 320,
                "thresholds": {
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                  "increaseFactor": 1.100000023841858,
                  "initialValue": 0.0,
                  "max": 0.0,
                  "min": 0.0
                },
                "type": 0
              },
              "featureMaintainer": {
                "enable": true,
                "lostFeatureErrorThreshold": 50000.0,
                "minimumDistanceBetweenFeatures": 50.0,
                "trackedFeatureThreshold": 200000.0
              },
              "motionEstimator": {
                "enable": false,
                "opticalFlow": {
                  "epsilon": 0.009999999776482582,
                  "maxIterations": 9,
                  "pyramidLevels": 0,
                  "searchWindowHeight": 5,
                  "searchWindowWidth": 5
                },
                "type": 0
              }
            },
            "numMemorySlices": 1,
            "numShaves": 1
          }
        }
      ],
      [
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        {
          "id": 4,
          "ioInfo": [
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              [
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                "in"
              ],
              {
                "blocking": true,
                "group": "",
                "id": 17,
                "name": "in",
                "queueSize": 8,
                "type": 3,
                "waitForMessage": true
              }
            ]
          ],
          "name": "XLinkOut",
          "properties": {
            "maxFpsLimit": -1.0,
            "metadataOnly": false,
            "streamName": "passthroughFrameLeft"
          }
        }
      ],
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                "type": 3,
                "waitForMessage": true
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            ]
          ],
          "name": "XLinkOut",
          "properties": {
            "maxFpsLimit": -1.0,
            "metadataOnly": false,
            "streamName": "trackedFeaturesLeft"
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            ]
          ],
          "name": "XLinkOut",
          "properties": {
            "maxFpsLimit": -1.0,
            "metadataOnly": false,
            "streamName": "passthroughFrameRight"
          }
        }
      ],
      [
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        {
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          "ioInfo": [
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              [
                "",
                "in"
              ],
              {
                "blocking": true,
                "group": "",
                "id": 20,
                "name": "in",
                "queueSize": 8,
                "type": 3,
                "waitForMessage": true
              }
            ]
          ],
          "name": "XLinkOut",
          "properties": {
            "maxFpsLimit": -1.0,
            "metadataOnly": false,
            "streamName": "trackedFeaturesRight"
          }
        }
      ],
      [
        8,
        {
          "id": 8,
          "ioInfo": [
            [
              [
                "",
                "out"
              ],
              {
                "blocking": false,
                "group": "",
                "id": 21,
                "name": "out",
                "queueSize": 8,
                "type": 0,
                "waitForMessage": false
              }
            ]
          ],
          "name": "XLinkIn",
          "properties": {
            "maxDataSize": 5242880,
            "numFrames": 8,
            "streamName": "trackedFeaturesConfig"
          }
        }
      ]
    ]
  }
}
```

### Need assistance?

Head over to [Discussion Forum](https://discuss.luxonis.com/) for technical support or any other questions you might have.