# \#math

**URL:** https://forum.opencv.org/tag/math/290.md

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## [Understanding the demo on homography from camera displacement](https://forum.opencv.org/t/understanding-the-demo-on-homography-from-camera-displacement/5043)

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**Author:** [@serhannn](https://forum.opencv.org/u/serhannn)\
**Replies:** 6\
**Last updated:** [August 23, 2023, 10:17am UTC](https://forum.opencv.org/t/understanding-the-demo-on-homography-from-camera-displacement/5043 "2023-08-23T10:17:43Z")

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Hi, I’m going through the demo 3 here on how to compute homography from camera displacement i…e, two different camera poses. I checked the derivation of the given equation to compute homography on the linked Wikipedia…

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## [solvePnP rotational vector](https://forum.opencv.org/t/solvepnp-rotational-vector/9590)

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**Author:** [@Carlos144Green](https://forum.opencv.org/u/Carlos144Green)\
**Replies:** 10\
**Last updated:** [July 22, 2022, 3:34pm UTC](https://forum.opencv.org/t/solvepnp-rotational-vector/9590 "2022-07-22T15:34:59Z")

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So I am following this #project, the result video is at the end. I want a way to extract the global 3d coordinates of the nose and the vector pointing away. I understand that we get the translational vector (which is th…

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## [Question in initUndistortRectifyMap source code](https://forum.opencv.org/t/question-in-initundistortrectifymap-source-code/9278)

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**Author:** [@jumby](https://forum.opencv.org/u/jumby)\
**Replies:** 4\
**Last updated:** [June 23, 2022, 3:34pm UTC](https://forum.opencv.org/t/question-in-initundistortrectifymap-source-code/9278 "2022-06-23T15:34:03Z")

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anyone here to help me figure out it in // HERE? why it be this way? anyone help? void cv::initUndistortRectifyMap( InputArray \_cameraMatrix, InputArray \_distCoeffs, InputArray \_matR, Inp…

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## [What values to use for a CGI virtual camera matrix?](https://forum.opencv.org/t/what-values-to-use-for-a-cgi-virtual-camera-matrix/6080)

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**Author:** [@MattWTSN](https://forum.opencv.org/u/MattWTSN)\
**Replies:** 4\
**Last updated:** [November 9, 2021, 6:16pm UTC](https://forum.opencv.org/t/what-values-to-use-for-a-cgi-virtual-camera-matrix/6080 "2021-11-09T18:16:27Z")

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I’m generating some virtual camera captures made with a 3d cgi software to test my code with zero issues introduced by the camera itself, such as defocus, noise and lens distortion. Such 3d cameras have zero distortion …

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## [Composing perspective transforms](https://forum.opencv.org/t/composing-perspective-transforms/5112)

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**Author:** [@pauljurczak](https://forum.opencv.org/u/pauljurczak)\
**Replies:** 2\
**Last updated:** [September 9, 2021, 12:44am UTC](https://forum.opencv.org/t/composing-perspective-transforms/5112 "2021-09-09T00:44:12Z")

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I have 2 matrices, such that: v1 = cv2.perspectiveTransform(v0, M0) v2 = cv2.perspectiveTransform(v1, M1) How can I get matrix M, such that: v2 = cv2.perspectiveTransform(v0, M) M0\*M1 or M1\*M0 doesn’t work.