diff --git a/openglcanvas.cpp b/openglcanvas.cpp
index 2288d04e1fe79fae958e94a6449a127a1bc7e172..b18d88144ef43eead08e5a1048cc8b58aa9a56af 100644
--- a/openglcanvas.cpp
+++ b/openglcanvas.cpp
@@ -709,6 +709,12 @@ void OpenGLCanvas::setShaders() {
 
     GLuint p = glCreateProgram();
 
+    // Bind attributes zblambda and zbR to the vertex shader
+    glVertexAttrib1f(0,zblambda);
+    glBindAttribLocation(p,0,"zblambda");
+    glVertexAttrib1f(1,zbR);
+    glBindAttribLocation(p,1,"zbR");
+
     glAttachShader(p,v);
     glAttachShader(p,f);
 
diff --git a/shaders/test_vertex_shader.vert b/shaders/test_vertex_shader.vert
index 40a52907ad38362c51113583529374db380f4836..6f057b2d093af290f95c117f8facb13c6d226773 100644
--- a/shaders/test_vertex_shader.vert
+++ b/shaders/test_vertex_shader.vert
@@ -6,7 +6,9 @@ float u, v, x, y, z;
 varying float r, theta, s;
 float lambda, phi;
 float extent, scale, vis_mode, center_lambda, center_phi;
-varying float zblambda,zbr,zbR,zbalpha,zbrho;
+float zbr,zbalpha,zbrho;
+/*attribute*/ float zblambda;
+/*attribute*/ float zbR;
 
 void main(void){
 
@@ -85,7 +87,6 @@ void main(void){
         u=x/(-z);
         v=y/(-z);
         // Z-B transformation
-        // TODO: read zblambda and zbR from the interface
         zblambda=0.1;
         zbR=1.0;
         zbalpha=atan(v,u);