diff --git a/openglcanvas.cpp b/openglcanvas.cpp
index 0b4ce7e25ff3842cc3d0ac718b90b0f993f95e92..16097fa71db18a8d8e60d8eee2b4ec72526ef03b 100644
--- a/openglcanvas.cpp
+++ b/openglcanvas.cpp
@@ -505,7 +505,6 @@ void OpenGLCanvas::vertex_transformation(float *positions, int m, int n, float c
                 positions[3*(j+i*n)+2] = z;
             }
 
-            // perspective
             if (visualization=="Zorin-Barr"){
                 // perspective
                 u = x/(-z);
diff --git a/shaders/vertex_shader.vert b/shaders/vertex_shader.vert
index 26a58d7af4f4d6e966d77d8501c7bdd93277d72f..964f1c388e7cf80d81c05e9c2285605c7aee1c92 100644
--- a/shaders/vertex_shader.vert
+++ b/shaders/vertex_shader.vert
@@ -71,8 +71,8 @@ void main(void){
     else if (vis_mode==3.0) // Equi-Rectangular
         gl_Position = vec4(lambda,phi,z,1.0);
     else if (vis_mode==4.0) { // Stereographic
-        u = 2.f*x/(-z+1);
-        v = 2.f*y/(-z+1);
+        u = 2.0*x/(-z+1.0);
+        v = 2.0*y/(-z+1.0);
         gl_Position = vec4(u/extent,v/extent,z,1.0);
     }
     else if (vis_mode==5.0) { // Mercator