Resize Window But Not Models

Hy Guys,

I have a Problem. Right now I try to implement my own small 2D-Game. I would like to change the windows size (e.g. going to full screen). However I also want that the size of the models do not change. Therefore I wrote a function to do all the necessary settings:

void basicOpenGLOperations::checkWindowSize(void){

	ViewRatio = static_cast<GLfloat>(WindowWidth)/static_cast<GLfloat>(WindowHeight);
	ProjectionMatrix = glm::perspective(ViewField,ViewRatio,0.1f,100.0f);

	glOrtho(-1.0,                                          // Left
              1.0,                                          // Right
             -1.0 / (WindowWidth / WindowHeight),   // Bottom
              1.0 / (WindowWidth / WindowHeight),   // Top
              0.01,                                         // Near
              10000.0);                                     // Far
        glViewport(0, 0, WindowWidth, WindowHeight);

All models are actual rectangle (2xTriangles) with textures. Interestingly, everything works fine works fine if I only change the width of the window. However if I change the height all models are resized as well