diff --git a/include/Kyoto/Math/CPlane.hpp b/include/Kyoto/Math/CPlane.hpp
index 58f6f657..2eb7775f 100644
--- a/include/Kyoto/Math/CPlane.hpp
+++ b/include/Kyoto/Math/CPlane.hpp
@@ -9,7 +9,7 @@
 class CPlane {
 public:
   CPlane(const CVector3f&, const CUnitVector3f&); // TODO weak
-  CPlane(float, const CUnitVector3f&);            // TODO weak
+  CPlane(float constant, const CUnitVector3f& normal) : x0_normal(normal), xc_constant(constant) {}
   CPlane(const CVector3f&, const CVector3f&, const CVector3f&);
   // TODO
 
diff --git a/include/WorldFormat/CCollisionSurface.hpp b/include/WorldFormat/CCollisionSurface.hpp
index 97a62fc1..42b8290e 100644
--- a/include/WorldFormat/CCollisionSurface.hpp
+++ b/include/WorldFormat/CCollisionSurface.hpp
@@ -4,17 +4,22 @@
 #include "types.h"
 
 #include "Kyoto/Math/CVector3f.hpp"
+#include "Kyoto/Math/CPlane.hpp"
 
 class CCollisionSurface {
 public:
-  typedef CVector3f TVerts[3];
 
-  // TODO
+  CCollisionSurface(const CVector3f&, const CVector3f&, const CVector3f&, uint flags);
+
+  CUnitVector3f GetNormal() const;
+  CPlane GetPlane() const;
 
 private:
-  TVerts x0_data;
+  CVector3f x0_a;
+  CVector3f xc_b;
+  CVector3f x18_c;
   uint x24_flags;
 };
-CHECK_SIZEOF(CCollisionSurface, 0x28)
+//CHECK_SIZEOF(CCollisionSurface, 0x28)
 
 #endif // _CCOLLISIONSURFACE
diff --git a/src/WorldFormat/CCollisionSurface.cpp b/src/WorldFormat/CCollisionSurface.cpp
new file mode 100644
index 00000000..9eba175a
--- /dev/null
+++ b/src/WorldFormat/CCollisionSurface.cpp
@@ -0,0 +1,16 @@
+#include "WorldFormat/CCollisionSurface.hpp"
+
+CCollisionSurface::CCollisionSurface(const CVector3f& a, const CVector3f& b, const CVector3f& c,
+                                     uint flags)
+: x0_a(a), xc_b(b), x18_c(c), x24_flags(flags) {}
+
+CUnitVector3f CCollisionSurface::GetNormal() const {
+  CVector3f baDiff = xc_b - x0_a;
+  CVector3f caDiff = x18_c - x0_a;
+  CVector3f tmp = CVector3f::Cross(baDiff, caDiff);
+  return tmp;
+}
+CPlane CCollisionSurface::GetPlane() const {
+  const CUnitVector3f norm = GetNormal();
+  return CPlane(CVector3f::Dot(norm, x0_a), norm);
+}