# Using Camera **URL:** \ **Category:** PowerVR Insider\ **Created:** [June 25, 2013, 6:34am UTC](https://forums.imgtec.com/t/using-camera/1818 "2013-06-25T06:34:27Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 6:34am UTC](https://forums.imgtec.com/t/using-camera/1818/1 "2013-06-25T06:34:27Z")
Hi, I have a rectangle rendered. I want to move the camera along the line cutting the rectangle into half, say 0.1 units per frame. I went through the IntroducingPOD sample program. The problem is that the program uses **CPVRTModelPOD** class and hence has functions to get the world matrices etc. I have all the vertex data and index data stored in 2D arrays. I don’t know how to start the navigation of camera. Can someone help ? ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 7:55am UTC](https://forums.imgtec.com/t/using-camera/1818/2 "2013-06-25T07:55:20Z")
Hi everything is in the sample about camera ,did you change the value of **vFrom** over the time ? (maybe a nice as a plus Lerp function will make it ) regards david ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 7:56am UTC](https://forums.imgtec.com/t/using-camera/1818/3 "2013-06-25T07:56:49Z")
all the beginner samples are superbe 🙂 i am still looking at it everyday 🙂 ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 8:10am UTC](https://forums.imgtec.com/t/using-camera/1818/4 "2013-06-25T08:10:24Z")
some nice easing function for your camera : [http://gizma.com/easing/](http://gizma.com/easing/) ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 8:45am UTC](https://forums.imgtec.com/t/using-camera/1818/5 "2013-06-25T08:45:58Z")
The function for navigation is not a problem for me. The problem is that I have prepared the “View” and the “Projection” matrices as : PVRTMat4 ViewMatrix = PVRTMat4::LookAtRH(vFrom, vTo, vUp); PVRTMat4 ProjectionMatrix = PVRTMat4::PerspectiveFovRH(DEG2RAD(fFOV), AspectRatio, CameraNear, CameraFar, PVRTMat4::OGL, rotate); PVRTMat4 ViewProjectionMatrix = ProjectionMatrix \* ViewMatrix; But I don’t know what the “Model” matrix means and how should it be prepared. Additionally, I have passed the matrix as : int i32Location = glGetUniformLocation(m\_uiProgramObject, “myPMVMatrix”); glUniformMatrix4fv(i32Location, 1, GL\_FALSE, ViewProjectionMatrix.ptr()); Is this correct ? ---
**Author:** ![JoeDavis](https://sea1.discourse-cdn.com/flex015/user_avatar/forums.imgtec.com/joedavis/32/71_2.png) [@JoeDavis](https://forums.imgtec.com/u/JoeDavis)\ **Post date:** [June 25, 2013, 8:58am UTC](https://forums.imgtec.com/t/using-camera/1818/6 "2013-06-25T08:58:34Z")
Hi, View & Projection matrices describe the camera position & how it sees the scene. The Model matrix (a.k.a. World matrix) describes your objects position in the scene, for example if it should be translated from it’s default position (0,0,0). ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 9:05am UTC](https://forums.imgtec.com/t/using-camera/1818/7 "2013-06-25T09:05:35Z")
So, the matrix which is passed through glUniformMatrix4fv() is (P_M_V) or (P\*V) ? Where should the model matrix be translated to from its default position ? ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 10:01am UTC](https://forums.imgtec.com/t/using-camera/1818/8 "2013-06-25T10:01:21Z")
Hello ````auto mTrans = PVRTMat4::Translation (x,y,z) for instance and
mMVP = m_mProjection * mTrans * m_mView; ```
of course the view is define by

m_mView = PVRTMat4::LookAtRH(vFrom, vTo, vUp);

the model-view-projection matrix is pass to the shader to transform the vertices
example :
glUniformMatrix4fv(Uniforms[j].nLocation, 1, GL_FALSE, mMVP.f);
regards
david ```` ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 10:28am UTC](https://forums.imgtec.com/t/using-camera/1818/9 "2013-06-25T10:28:28Z")
Thanks David, but I can’t understand the idea behind translating the model matrix in the first place. Why is it needed ? Sorry for being so noob. What is the difference between mMVP.f and mMVP.ptr() ? ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 10:45am UTC](https://forums.imgtec.com/t/using-camera/1818/10 "2013-06-25T10:45:44Z")
No worry man, from the doc ````auto f= Array of float
ptr=pointer to an array of float or element
```
```` ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 10:56am UTC](https://forums.imgtec.com/t/using-camera/1818/11 "2013-06-25T10:56:18Z")
And about the model matrix ? ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 11:09am UTC](https://forums.imgtec.com/t/using-camera/1818/12 "2013-06-25T11:09:46Z")
define your model view matrix as PVRTMat4 mMVP; mMVP = m\_mProjection \* mTrans \* m\_mView; The SDK provide a lot of sample about it , i am sure you will find the answer there as well regards david ps [http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/#The\_Model\_matrix](http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/#The_Model_matrix) ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 11:11am UTC](https://forums.imgtec.com/t/using-camera/1818/13 "2013-06-25T11:11:59Z")
No, that’s not my question. I asked why is the translation (mTrans = PVRTMat4::Translation (x,y,z)) required ? ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 11:21am UTC](https://forums.imgtec.com/t/using-camera/1818/14 "2013-06-25T11:21:01Z")
in the demo your were looking at you saw // Pass the model-view-projection matrix (MVP) to the shader to transform the vertices ````auto PVRTMat4 mModelView, mMVP;
mModelView = mView * mWorld;
mMVP = mProjection * mModelView;
glUniformMatrix4fv(m_ShaderProgram.uiMVPMatrixLoc, 1, GL_FALSE, mMVP.f); ```

like is said before as well you could change your view model only by changing the vFrom value depending where you camera should be.

the translation that i introduce was to make life easier to move the camera as you like but it s not mandatory..a simple matrix calculation here

```` ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 11:29am UTC](https://forums.imgtec.com/t/using-camera/1818/15 "2013-06-25T11:29:38Z")
Some more questions. 1. How is mWorld defined ? 2. Will there be as many model matrices as there are meshes in the scene ? If yes, what will the model matrix be for a 3D box ? 3. Will the values of x,y,z in Translation(x,y,z) be the coordinates of vFrom ? ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 25, 2013, 11:34am UTC](https://forums.imgtec.com/t/using-camera/1818/16 "2013-06-25T11:34:48Z")
i see , i think this question is more related to the understanding of rendering using gl [http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/#The\_Model\_\_View\_and\_Projection\_matrices](http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/#The_Model__View_and_Projection_matrices) regards david ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 25, 2013, 11:54am UTC](https://forums.imgtec.com/t/using-camera/1818/17 "2013-06-25T11:54:12Z")
OK. I think I got the use of model matrix. Its basically used to transform the objects vertices from local space to world space. But, still I can’t figure out what mWorld for my scene will contain. I have a 3D box with its base centered at origin and four rectangles in x-y plane surrounding the base of the box. We can think it as a building with streets on all its four sides. What will be the mWorld matrix for such a scene? I want to navigate camera on the streets on all the four sides. ---
**Author:** ![hellboy](https://avatars.discourse-cdn.com/v4/letter/h/48db29/32.png) [@hellboy](https://forums.imgtec.com/u/hellboy)\ **Post date:** [June 26, 2013, 7:04am UTC](https://forums.imgtec.com/t/using-camera/1818/18 "2013-06-26T07:04:25Z")
I finally prepared the model matrix for every object and translated it to the origin. Then, in a loop, I prepared the PMV matrix by multiplying all the three matrices together and passed it to the shader for every object. I think, I got the camera working now. Thanks. ---
**Author:** ![dgu](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@dgu](https://forums.imgtec.com/u/dgu)\ **Post date:** [June 26, 2013, 7:16am UTC](https://forums.imgtec.com/t/using-camera/1818/19 "2013-06-26T07:16:35Z")
super cool