# Perspective Transform

This function block lets you interactively define a four-point perspective mapping on an image and produce a rectified (top‑down) view plus the transform matrix. Use it when you need to remove perspective distortion or generate a bird’s-eye view from a photographed plane.

## 📥 Inputs <a href="#inputs" id="inputs"></a>

This block accepts the following input socket:

* `Image Any`\
  The source image used to pick the four reference points and compute the perspective transform.

## 📤 Outputs <a href="#outputs" id="outputs"></a>

This block provides the following output sockets:

* `Image Any`\
  The warped (perspective‑corrected) image produced after four points are defined. Empty until four points are set.
* `Transform Matrix`\
  The perspective transform matrix that can be reused by other blocks that accept a transform or perspective matrix.

## 🕹️ Controls <a href="#controls" id="controls"></a>

* `Image Preview`\
  Click on the preview area to place points on the image.
* `Place Points (mouse left click)`\
  Place up to four points in the displayed image.
* `Undo (U)`\
  Remove the most recently placed point.
* `Clear (C)`\
  Remove all placed points and start over.
* `Point Markers and Lines`\
  Visual markers and connecting lines are drawn on the preview so you can see the selected polygon before generating the output.

Tip: Select four points starting from the bottom‑left and proceed clockwise for predictable results.

## 🎨 Features <a href="#features" id="features"></a>

* Interactive point selection directly on the image preview for intuitive setup.
* Visual feedback with circles and connecting lines so you can verify point order and placement.
* Outputs both a rectified image and the transform matrix for downstream processing or reuse.
* Point selection is persisted so you can save and reload your configuration.

## ⚙️ Running mechanism <a href="#running-mechanism" id="running-mechanism"></a>

1. Provide an image to the `Image Any` input socket.
2. Click on the preview to place up to four reference points. Use `U` to undo and `C` to clear.
3. Once four points are placed (recommended order: bottom‑left, then clockwise), the block computes the perspective mapping and outputs the rectified image on the `Image Any` output and the mapping on the `Transform Matrix` output.
4. The transform matrix can be consumed by other blocks that accept a perspective or transform matrix.

## 📝 Usage Instructions <a href="#usage" id="usage"></a>

1. Connect a camera or image source to the `Image Any` input.
2. Run once so the image appears in the preview.
3. Click four points on the image in the required order (bottom‑left → clockwise).
4. Inspect the preview; when four points are present the rectified image appears on the output.
5. Use the `Transform Matrix` output for measurements, metric corrections or other perspective‑aware tasks.

## 💡 Tips and Tricks <a href="#tips-and-tricks" id="tips-and-tricks"></a>

* Combine with `Show Image` to inspect the selected area in a larger viewer before or after placing points.
* Use `Image ROI Select` or `Image ROI` to crop a region first if you want to limit the interactive point picking to a smaller area.
* Feed the `Transform Matrix` output into `Social Distance Detector` (as the `Perspective Matrix`) to enable accurate distance measurements in world coordinates.
* After rectifying, use `Image Resize` to scale the result for downstream processing or to match other blocks’ expected sizes.
* If you need to extract the rectified region back into other processing steps, pair with `Get ROI` to pass the corrected image into analysis blocks.

## 🛠️ Troubleshooting <a href="#troubleshooting" id="troubleshooting"></a>

* If the output is blank or not appearing: ensure an image is connected and visible in the preview, then place four points.
* If the rectified output looks skewed: verify the point order (start bottom‑left and go clockwise) and reposition points using `Undo (U)` or `Clear (C)` and retry.
* If measurements appear incorrect downstream: confirm you passed the block’s `Transform Matrix` to blocks that require a perspective matrix and that the matrix corresponds to the same image used for picking points.


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