在ios端利用opengl建模，成功展示了一个3d模型，update内容如下

CGSize size = self.view.bounds.size; float aspect = fabs(size.width / size.height); GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(bigSize), aspect, 1.0f, 10.0f);//GLKMathDegreesToRadians值越大，模型越小(0-180) self.effect.transform.projectionMatrix = projectionMatrix; GLKMatrix4 modelViewMatrix = GLKMatrix4Translate(GLKMatrix4Identity, 0.0f, 0.0f, 0.0f); modelViewMatrix = GLKMatrix4Translate(modelViewMatrix, 0.0f, 0.0f, -2.0f); //平移 modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, _rotation, 0.1f, xxx, 1.0f); //旋转 GLKMatrix4 modelViewProjectionMatrix = GLKMatrix4Multiply(projectionMatrix, modelViewMatrix); GLint mat = glGetUniformLocation(0.0f, "modelViewProjectionMatrix"); glUniformMatrix4fv(mat, 1, GL_FALSE, modelViewProjectionMatrix.m);`

由于物体的坐标位置是在屏幕坐标范围外的，所以看不到物体。如何设置当物体显示的时候，物体实在屏幕中央？
简而言之，如何改变物体的中心点坐标或者某点坐标为屏幕中心点坐标？