# Converting 3D to 2D from a specific viewpoint

**URL:** <https://forum.opencv.org/t/converting-3d-to-2d-from-a-specific-viewpoint/10931>\
**Category:** Uncategorized\
**Created:** [November 13, 2022, 4:01am UTC](https://forum.opencv.org/t/converting-3d-to-2d-from-a-specific-viewpoint/10931 "2022-11-13T04:01:06Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![elvintoh82](https://avatars.discourse-cdn.com/v4/letter/e/bbce88/32.png) [@elvintoh82](https://forum.opencv.org/u/elvintoh82)\
**Post date:** [November 13, 2022, 4:01am UTC](https://forum.opencv.org/t/converting-3d-to-2d-from-a-specific-viewpoint/10931/1 "2022-11-13T04:01:06Z")

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Following the tutorials and tonnes of videos, I was able to combine an rgb and depth image, conduct the calibration (with many images) to construct a point cloud.

Within Open3D (I know this forum is OpenCV) and within the pointcloud, I was able to identify a particular surface of interest, find it’s plane/perpendicular/normal (Z-vector) using o3d.segment\_plane() and I was also able to draw an arrow for visualisation purposes. FYI, it was able to calculate the complete A, B, C, D of the plane equation.

Since I have the Z-vector, I would like to next construct the X-vector, which in concept, can be easily found if we were to use cv2.minAreaRect() on a 2D image.

What I have:

1. The filtered pointcloud (inliers only)
2. A specific location of the center of the surface (Tvec)
3. It’s orientation (Rvec) or plane equation ABCD

**How do I attain a 2D image of the filtered pointcloud, from a viewpoint along the Z-vector, looking straight down at the surface.**

The purpose is so that I can subsequently use cv2.minAreaRect() to get an angle to construct the X-vector.

What I have already tried:

1. I’ve tried cv2.projectPoints() but the resulting x and y coordinates for each of the points attained were ridiculously far (like x: -300,000 and y: -300,000)

Could anyone guide me on what needs to be done so that I can achieve such a 2D image by converting from 3D back to 2D from a specific viewpoint please?

![ScreenCapture_2022-11-13-11-43-18](https://us1.discourse-cdn.com/flex020/uploads/opencv/original/2X/3/39de5ec9b7c1bfa1dd82f850df0b6a366fb4ff1f.png)