diff --git a/src/FlatLayerVisualisation.cpp b/src/FlatLayerVisualisation.cpp
index 0c1a3f1..120c15d 100644
--- a/src/FlatLayerVisualisation.cpp
+++ b/src/FlatLayerVisualisation.cpp
@@ -21,6 +21,7 @@ static inline void computeColor(float intensity, float limit, float* destination
 }
 
 FlatLayerVisualisation::FlatLayerVisualisation(const LayerData &layer, Ordering ordering) :
+        LayerVisualisation(layer.numEntries()),
         ordering(ordering),
         faceCount(layer.numEntries() * 4),
         vertexBuffer(new float[faceCount * 3]),
@@ -78,7 +79,7 @@ void FlatLayerVisualisation::render()
     glDisableClientState(GL_COLOR_ARRAY);
 }
 
-void FlatLayerVisualisation::setVertexPositions(int vertexNo, float *destination)
+void FlatLayerVisualisation::setVertexPositions(const int vertexNo, float *destination)
 {
     int j = 0;
     float zOffset;
@@ -100,6 +101,12 @@ void FlatLayerVisualisation::setVertexPositions(int vertexNo, float *destination
             break;
     }
 
+    nodePositions_[3 * vertexNo] = 0;
+    nodePositions_[3 * vertexNo + 1] = yOffset;
+    nodePositions_[3 * vertexNo + 2] = zOffset;
+    // TODO: actually compute from this rather than copying to destination.
+    // Side note: should move this out of this function anyway.
+
     // Create the 4 vertices for the pyramid
     destination[j++] = -0.5f;
     destination[j++] = 0 + yOffset; 
diff --git a/src/FlatLayerVisualisation.hpp b/src/FlatLayerVisualisation.hpp
index d98a355..4a40d76 100644
--- a/src/FlatLayerVisualisation.hpp
+++ b/src/FlatLayerVisualisation.hpp
@@ -26,6 +26,6 @@ namespace fmri
         std::unique_ptr<float[]> colorBuffer;
         std::unique_ptr<int[]> indexBuffer;
 
-        void setVertexPositions(int vertexNo, float* destination);
+        void setVertexPositions(const int vertexNo, float *destination);
     };
 }
diff --git a/src/LayerVisualisation.cpp b/src/LayerVisualisation.cpp
new file mode 100644
index 0000000..3dcabc7
--- /dev/null
+++ b/src/LayerVisualisation.cpp
@@ -0,0 +1,11 @@
+#include "LayerVisualisation.hpp"
+
+const std::vector<float> &fmri::LayerVisualisation::nodePositions() const
+{
+    return nodePositions_;
+}
+
+fmri::LayerVisualisation::LayerVisualisation(size_t numNodes)
+        : nodePositions_(numNodes * 3)
+{
+}
diff --git a/src/LayerVisualisation.hpp b/src/LayerVisualisation.hpp
index 170bf17..d3b2677 100644
--- a/src/LayerVisualisation.hpp
+++ b/src/LayerVisualisation.hpp
@@ -1,12 +1,20 @@
 #pragma once
 
+#include <vector>
+
 namespace fmri
 {
     class LayerVisualisation
     {
     public:
+        LayerVisualisation() = default;
+        LayerVisualisation(size_t numNodes);
         virtual ~LayerVisualisation() = default;
 
         virtual void render() = 0;
+        virtual const std::vector<float>& nodePositions() const;
+
+    protected:
+        std::vector<float> nodePositions_;
     };
 }