diff --git a/clear_cmd.c b/clear_cmd.c
index 1f46a071df..6d1016daa0 100644
--- a/clear_cmd.c
+++ b/clear_cmd.c
@@ -534,9 +534,12 @@ static void DrawTile_Clear(TileInfo *ti)
 	DrawClearLandFence(ti);
 }
 
-static uint GetSlopeZ_Clear(const TileInfo* ti)
+static uint GetSlopeZ_Clear(TileIndex tile, uint x, uint y)
 {
-	return GetPartialZ(ti->x & 0xF, ti->y & 0xF, ti->tileh) + ti->z;
+	uint z;
+	uint tileh = GetTileSlope(tile, &z);
+
+	return z + GetPartialZ(x & 0xF, y & 0xF, tileh);
 }
 
 static Slope GetSlopeTileh_Clear(TileIndex tile, Slope tileh)
diff --git a/dummy_land.c b/dummy_land.c
index 1052cde0a7..88daa07525 100644
--- a/dummy_land.c
+++ b/dummy_land.c
@@ -14,7 +14,7 @@ static void DrawTile_Dummy(TileInfo *ti)
 }
 
 
-static uint GetSlopeZ_Dummy(const TileInfo* ti)
+static uint GetSlopeZ_Dummy(TileIndex tile, uint x, uint y)
 {
 	return 0;
 }
diff --git a/industry_cmd.c b/industry_cmd.c
index fe7e79d458..dfc366c6f9 100644
--- a/industry_cmd.c
+++ b/industry_cmd.c
@@ -267,9 +267,9 @@ static void DrawTile_Industry(TileInfo *ti)
 	}
 }
 
-static uint GetSlopeZ_Industry(const TileInfo *ti)
+static uint GetSlopeZ_Industry(TileIndex tile, uint x, uint y)
 {
-	return ti->z + (ti->tileh == SLOPE_FLAT ? 0 : TILE_HEIGHT);
+	return GetTileMaxZ(tile);
 }
 
 static Slope GetSlopeTileh_Industry(TileIndex tile, Slope tileh)
diff --git a/landscape.c b/landscape.c
index 753e24d487..e6608fa5e1 100644
--- a/landscape.c
+++ b/landscape.c
@@ -174,11 +174,9 @@ uint GetPartialZ(int x, int y, Slope corners)
 
 uint GetSlopeZ(int x, int y)
 {
-	TileInfo ti;
+	TileIndex tile = TileVirtXY(x, y);
 
-	FindLandscapeHeight(&ti, x, y);
-
-	return _tile_type_procs[ti.type]->get_slope_z_proc(&ti);
+	return _tile_type_procs[GetTileType(tile)]->get_slope_z_proc(tile, x, y);
 }
 
 
diff --git a/openttd.h b/openttd.h
index d0062fd3f6..c72cbc0a4a 100644
--- a/openttd.h
+++ b/openttd.h
@@ -298,7 +298,7 @@ typedef struct {
 
 
 typedef void DrawTileProc(TileInfo *ti);
-typedef uint GetSlopeZProc(const TileInfo* ti);
+typedef uint GetSlopeZProc(TileIndex tile, uint x, uint y);
 typedef int32 ClearTileProc(TileIndex tile, byte flags);
 typedef void GetAcceptedCargoProc(TileIndex tile, AcceptedCargo res);
 typedef void GetTileDescProc(TileIndex tile, TileDesc *td);
diff --git a/rail_cmd.c b/rail_cmd.c
index 1dd401df6a..338742b251 100644
--- a/rail_cmd.c
+++ b/rail_cmd.c
@@ -1692,20 +1692,20 @@ void SetSignalsOnBothDir(TileIndex tile, byte track)
 	UpdateSignalsOnSegment(tile, _search_dir_2[track]);
 }
 
-static uint GetSlopeZ_Track(const TileInfo* ti)
+static uint GetSlopeZ_Track(TileIndex tile, uint x, uint y)
 {
-	Slope tileh = ti->tileh;
-	uint z = ti->z;
+	uint z;
+	Slope tileh = GetTileSlope(tile, &z);
 
 	if (tileh == SLOPE_FLAT) return z;
-	if (IsPlainRailTile(ti->tile)) {
-		uint f = GetRailFoundation(ti->tileh, GetTrackBits(ti->tile));
+	if (IsPlainRailTile(tile)) {
+		uint f = GetRailFoundation(tileh, GetTrackBits(tile));
 
 		if (f != 0) {
 			if (f < 15) return z + TILE_HEIGHT; // leveled foundation
 			tileh = _inclined_tileh[f - 15]; // inclined foundation
 		}
-		return z + GetPartialZ(ti->x & 0xF, ti->y & 0xF, tileh);
+		return z + GetPartialZ(x & 0xF, y & 0xF, tileh);
 	} else {
 		return z + TILE_HEIGHT;
 	}
diff --git a/road_cmd.c b/road_cmd.c
index 4328aa277b..e4a725711b 100644
--- a/road_cmd.c
+++ b/road_cmd.c
@@ -833,20 +833,20 @@ void DrawRoadDepotSprite(int x, int y, DiagDirection dir)
 	}
 }
 
-static uint GetSlopeZ_Road(const TileInfo* ti)
+static uint GetSlopeZ_Road(TileIndex tile, uint x, uint y)
 {
-	Slope tileh = ti->tileh;
-	uint z = ti->z;
+	uint z;
+	Slope tileh = GetTileSlope(tile, &z);
 
 	if (tileh == SLOPE_FLAT) return z;
-	if (GetRoadTileType(ti->tile) == ROAD_TILE_NORMAL) {
-		uint f = GetRoadFoundation(tileh, GetRoadBits(ti->tile));
+	if (GetRoadTileType(tile) == ROAD_TILE_NORMAL) {
+		uint f = GetRoadFoundation(tileh, GetRoadBits(tile));
 
 		if (f != 0) {
 			if (f < 15) return z + TILE_HEIGHT; // leveled foundation
 			tileh = _inclined_tileh[f - 15]; // inclined foundation
 		}
-		return z + GetPartialZ(ti->x & 0xF, ti->y & 0xF, tileh);
+		return z + GetPartialZ(x & 0xF, y & 0xF, tileh);
 	} else {
 		return z + TILE_HEIGHT;
 	}
diff --git a/station_cmd.c b/station_cmd.c
index 1e8a4ea12b..305364df6a 100644
--- a/station_cmd.c
+++ b/station_cmd.c
@@ -2152,9 +2152,9 @@ void StationPickerDrawSprite(int x, int y, RailType railtype, int image)
 	}
 }
 
-static uint GetSlopeZ_Station(const TileInfo* ti)
+static uint GetSlopeZ_Station(TileIndex tile, uint x, uint y)
 {
-	return ti->z + (ti->tileh == SLOPE_FLAT ? 0 : TILE_HEIGHT);
+	return GetTileMaxZ(tile);
 }
 
 static Slope GetSlopeTileh_Station(TileIndex tile, Slope tileh)
diff --git a/town_cmd.c b/town_cmd.c
index 720918419c..f87f1917cf 100644
--- a/town_cmd.c
+++ b/town_cmd.c
@@ -110,9 +110,9 @@ static void DrawTile_Town(TileInfo *ti)
 	}
 }
 
-static uint GetSlopeZ_Town(const TileInfo* ti)
+static uint GetSlopeZ_Town(TileIndex tile, uint x, uint y)
 {
-	return ti->z + (ti->tileh == SLOPE_FLAT ? 0 : TILE_HEIGHT);
+	return GetTileMaxZ(tile);
 }
 
 static Slope GetSlopeTileh_Town(TileIndex tile, Slope tileh)
diff --git a/tree_cmd.c b/tree_cmd.c
index 9caf6b9d65..99b2de384d 100644
--- a/tree_cmd.c
+++ b/tree_cmd.c
@@ -323,9 +323,12 @@ static void DrawTile_Trees(TileInfo *ti)
 }
 
 
-static uint GetSlopeZ_Trees(const TileInfo* ti)
+static uint GetSlopeZ_Trees(TileIndex tile, uint x, uint y)
 {
-	return GetPartialZ(ti->x & 0xF, ti->y & 0xF, ti->tileh) + ti->z;
+	uint z;
+	uint tileh = GetTileSlope(tile, &z);
+
+	return z + GetPartialZ(x & 0xF, y & 0xF, tileh);
 }
 
 static Slope GetSlopeTileh_Trees(TileIndex tile, Slope tileh)
diff --git a/tunnelbridge_cmd.c b/tunnelbridge_cmd.c
index 8380b04672..bddc02d2d6 100644
--- a/tunnelbridge_cmd.c
+++ b/tunnelbridge_cmd.c
@@ -1089,13 +1089,13 @@ static void DrawTile_TunnelBridge(TileInfo *ti)
 	}
 }
 
-static uint GetSlopeZ_TunnelBridge(const TileInfo* ti)
+static uint GetSlopeZ_TunnelBridge(TileIndex tile, uint x, uint y)
 {
-	TileIndex tile = ti->tile;
-	uint z = ti->z;
-	uint x = ti->x & 0xF;
-	uint y = ti->y & 0xF;
-	Slope tileh = ti->tileh;
+	uint z;
+	Slope tileh = GetTileSlope(tile, &z);
+
+	x &= 0xF;
+	y &= 0xF;
 
 	if (IsTunnel(tile)) {
 		uint pos = (DiagDirToAxis(GetTunnelDirection(tile)) == AXIS_X ? y : x);
diff --git a/unmovable_cmd.c b/unmovable_cmd.c
index 7da8360418..0188900e65 100644
--- a/unmovable_cmd.c
+++ b/unmovable_cmd.c
@@ -176,12 +176,15 @@ static void DrawTile_Unmovable(TileInfo *ti)
 	}
 }
 
-static uint GetSlopeZ_Unmovable(const TileInfo* ti)
+static uint GetSlopeZ_Unmovable(TileIndex tile, uint x, uint y)
 {
-	if (IsOwnedLand(ti->tile)) {
-		return ti->z + GetPartialZ(ti->x & 0xF, ti->y & 0xF, ti->tileh);
+	if (IsOwnedLand(tile)) {
+		uint z;
+		uint tileh = GetTileSlope(tile, &z);
+
+		return z + GetPartialZ(x & 0xF, y & 0xF, tileh);
 	} else {
-		return ti->z + (ti->tileh == SLOPE_FLAT ? 0 : TILE_HEIGHT);
+		return GetTileMaxZ(tile);
 	}
 }
 
diff --git a/viewport.c b/viewport.c
index eb0cbe51e4..200098188b 100644
--- a/viewport.c
+++ b/viewport.c
@@ -294,7 +294,6 @@ ViewPort *IsPtInWindowViewport(const Window *w, int x, int y)
 
 static Point TranslateXYToTileCoord(const ViewPort *vp, int x, int y)
 {
-	int z;
 	Point pt;
 	int a,b;
 
@@ -314,16 +313,19 @@ static Point TranslateXYToTileCoord(const ViewPort *vp, int x, int y)
 	a = x+y;
 	b = x-y;
 #endif
-	z = GetSlopeZ(a, b) >> 1;
-	z = GetSlopeZ(a+z, b+z) >> 1;
-	z = GetSlopeZ(a+z, b+z) >> 1;
-	z = GetSlopeZ(a+z, b+z) >> 1;
-	z = GetSlopeZ(a+z, b+z) >> 1;
 
-	pt.x = a+z;
-	pt.y = b+z;
+	if ((uint)a < MapMaxX() * TILE_SIZE && (uint)b < MapMaxY() * TILE_SIZE) {
+		uint z;
 
-	if ((uint)pt.x >= MapMaxX() * TILE_SIZE || (uint)pt.y >= MapMaxY() * TILE_SIZE) {
+		z = GetSlopeZ(a,     b    ) / 2;
+		z = GetSlopeZ(a + z, b + z) / 2;
+		z = GetSlopeZ(a + z, b + z) / 2;
+		z = GetSlopeZ(a + z, b + z) / 2;
+		z = GetSlopeZ(a + z, b + z) / 2;
+
+		pt.x = a + z;
+		pt.y = b + z;
+	} else {
 		pt.x = pt.y = -1;
 	}
 
diff --git a/water_cmd.c b/water_cmd.c
index ca23cc84fb..834cfd1964 100644
--- a/water_cmd.c
+++ b/water_cmd.c
@@ -479,9 +479,12 @@ void DrawShipDepotSprite(int x, int y, int image)
 }
 
 
-static uint GetSlopeZ_Water(const TileInfo *ti)
+static uint GetSlopeZ_Water(TileIndex tile, uint x, uint y)
 {
-	return GetPartialZ(ti->x & 0xF, ti->y & 0xF, ti->tileh) + ti->z;
+	uint z;
+	uint tileh = GetTileSlope(tile, &z);
+
+	return z + GetPartialZ(x & 0xF, y & 0xF, tileh);
 }
 
 static Slope GetSlopeTileh_Water(TileIndex tile, Slope tileh)