diff --git a/LEGO1/viewmanager/viewmanager.cpp b/LEGO1/viewmanager/viewmanager.cpp
index 2ed3b448..31302284 100644
--- a/LEGO1/viewmanager/viewmanager.cpp
+++ b/LEGO1/viewmanager/viewmanager.cpp
@@ -2,6 +2,7 @@
 
 #include "mxdirectx/mxstopwatch.h"
 #include "tgl/d3drm/impl.h"
+#include "vec.h"
 #include "viewlod.h"
 
 DECOMP_SIZE_ASSERT(ViewManager, 0x1bc)
@@ -192,7 +193,7 @@ inline void ViewManager::FUN_100a66f0(ViewROI* p_roi, int p_und)
 
 		if (p_und == -1) {
 			if (p_roi->GetWorldBoundingSphere().Radius() > 0.001F) {
-				float und = FUN_100a6dc0(p_roi->GetWorldBoundingSphere());
+				float und = ProjectedSize(p_roi->GetWorldBoundingSphere());
 
 				if (und < seconds_allowed * g_unk0x1010105c) {
 					if (p_roi->GetUnknown0xe0() == -2) {
@@ -268,7 +269,7 @@ inline int ViewManager::Unknown()
 	}
 	else {
 		float fVar7 = tan(view_angle / 2.0F);
-		unk0x2c = view_angle * view_angle * 4.0F;
+		view_area_at_one = view_angle * view_angle * 4.0F;
 
 		float fVar1 = front * fVar7;
 		float fVar2 = (width / height) * fVar1;
@@ -433,11 +434,18 @@ void ViewManager::SetPOVSource(const OrientableROI* point_of_view)
 	}
 }
 
-// STUB: LEGO1 0x100a6dc0
-float ViewManager::FUN_100a6dc0(const BoundingSphere& p_bounding_sphere)
+// FUNCTION: LEGO1 0x100a6dc0
+float ViewManager::ProjectedSize(const BoundingSphere& p_bounding_sphere)
 {
-	// TODO
-	return 0.0F;
+	// The algorithm projects the radius of bounding sphere onto the perpendicular
+	// plane one unit in front of the camera. That value is simply the ratio of the
+	// radius to the distance from the camera to the sphere center. The projected size
+	// is then the ratio of the area of that projected circle to the view surface area
+	// at Z == 1.0.
+	//
+	float sphere_projected_area = 3.14159265359 * (p_bounding_sphere.Radius() * p_bounding_sphere.Radius());
+	float square_dist_to_sphere = DISTSQRD3(p_bounding_sphere.Center(), pov[3]);
+	return sphere_projected_area / view_area_at_one / square_dist_to_sphere;
 }
 
 // STUB: LEGO1 0x100a6e00
diff --git a/LEGO1/viewmanager/viewmanager.h b/LEGO1/viewmanager/viewmanager.h
index 69aaeebd..8a7e50d0 100644
--- a/LEGO1/viewmanager/viewmanager.h
+++ b/LEGO1/viewmanager/viewmanager.h
@@ -26,7 +26,7 @@ class ViewManager {
 	void FUN_100a65b0(ViewROI* p_roi, int p_und);
 	void FUN_100a66a0(ViewROI* p_roi);
 	void SetPOVSource(const OrientableROI* point_of_view);
-	float FUN_100a6dc0(const BoundingSphere& p_bounding_sphere);
+	float ProjectedSize(const BoundingSphere& p_bounding_sphere);
 	ViewROI* Pick(Tgl::View* p_view, unsigned long x, unsigned long y);
 	void SetResolution(int width, int height);
 	void SetFrustrum(float fov, float front, float back);
@@ -50,7 +50,7 @@ class ViewManager {
 	RealtimeView rt_view;     // 0x14
 	ROIList visible_rois;     // 0x18
 	float unk0x28;            // 0x28
-	float unk0x2c;            // 0x2c
+	float view_area_at_one;   // 0x2c
 	unsigned int flags;       // 0x30
 	float width;              // 0x34
 	float height;             // 0x38