diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 7155c98e6..9d2899d7e 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -4181,47 +4181,18 @@ bool DLevelScript::DoCheckActorTexture(int tid, AActor *activator, int string, b
 	}
 	int i, numff;
 	FTextureID secpic;
-	sector_t *sec = actor->Sector;
-	numff = sec->e->XFloor.ffloors.Size();
+	sector_t *resultsec;
+	F3DFloor *resffloor;
 
 	if (floor)
 	{
-		// Looking through planes from top to bottom
-		for (i = 0; i < numff; ++i)
-		{
-			F3DFloor *ff = sec->e->XFloor.ffloors[i];
-
-			if ((ff->flags & (FF_EXISTS | FF_SOLID)) == (FF_EXISTS | FF_SOLID) &&
-				actor->Z() >= ff->top.plane->ZatPoint(actor))
-			{ // This floor is beneath our feet.
-				secpic = *ff->top.texture;
-				break;
-			}
-		}
-		if (i == numff)
-		{ // Use sector's floor
-			secpic = sec->GetTexture(sector_t::floor);
-		}
+		actor->Sector->NextLowestFloorAt(actor, actor->Z(), &resultsec, &resffloor);
+		secpic = resffloor ? *resffloor->top.texture : resultsec->planes[sector_t::floor].Texture;
 	}
 	else
 	{
-		fixed_t z = actor->Top();
-		// Looking through planes from bottom to top
-		for (i = numff-1; i >= 0; --i)
-		{
-			F3DFloor *ff = sec->e->XFloor.ffloors[i];
-
-			if ((ff->flags & (FF_EXISTS | FF_SOLID)) == (FF_EXISTS | FF_SOLID) &&
-				z <= ff->bottom.plane->ZatPoint(actor))
-			{ // This floor is above our eyes.
-				secpic = *ff->bottom.texture;
-				break;
-			}
-		}
-		if (i < 0)
-		{ // Use sector's ceiling
-			secpic = sec->GetTexture(sector_t::ceiling);
-		}
+		actor->Sector->NextHighestCeilingAt(actor, actor->Top(), &resultsec, &resffloor);
+		secpic = resffloor ? *resffloor->bottom.texture : resultsec->planes[sector_t::ceiling].Texture;
 	}
 	return tex == TexMan[secpic];
 }
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index 1a4d218cf..51d007878 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -932,6 +932,74 @@ fixed_t sector_t::LowestFloorAt(fixed_t x, fixed_t y, sector_t **resultsec)
 }
 
 
+fixed_t sector_t::NextHighestCeilingAt(fixed_t x, fixed_t y, fixed_t z, sector_t **resultsec, F3DFloor **resultffloor)
+{
+	sector_t *sec = this;
+	while (true)
+	{
+		// Looking through planes from bottom to top
+		for (int i = sec->e->XFloor.ffloors.Size() - 1; i >= 0; --i)
+		{
+			F3DFloor *ff = sec->e->XFloor.ffloors[i];
+
+			fixed_t ffz = ff->bottom.plane->ZatPoint(x, y);
+			if ((ff->flags & (FF_EXISTS | FF_SOLID)) == (FF_EXISTS | FF_SOLID) && z <= ffz)
+			{ // This floor is above our eyes.
+				if (resultsec) *resultsec = sec;
+				if (resultffloor) *resultffloor = ff;
+				return ffz;
+			}
+		}
+		if (sec->PortalBlocksMovement(sector_t::ceiling))
+		{ // Use sector's floor
+			if (resultffloor) *resultffloor = NULL;
+			if (resultsec) *resultsec = sec;
+			return sec->ceilingplane.ZatPoint(x, y);
+		}
+		else
+		{
+			FDisplacement &disp = sec->CeilingDisplacement();
+			x += disp.pos.x;
+			y += disp.pos.y;
+		}
+	}
+}
+
+fixed_t sector_t::NextLowestFloorAt(fixed_t x, fixed_t y, fixed_t z, sector_t **resultsec, F3DFloor **resultffloor)
+{
+	sector_t *sec = this;
+	while (true)
+	{
+		// Looking through planes from top to bottom
+		unsigned numff = sec->e->XFloor.ffloors.Size();
+		for (unsigned i = 0; i < numff; ++i)
+		{
+			F3DFloor *ff = sec->e->XFloor.ffloors[i];
+
+			fixed_t ffz = ff->top.plane->ZatPoint(x, y);
+			if ((ff->flags & (FF_EXISTS | FF_SOLID)) == (FF_EXISTS | FF_SOLID) && z >= ffz)
+			{ // This floor is beneath our feet.
+				if (resultsec) *resultsec = sec;
+				if (resultffloor) *resultffloor = ff;
+				return ffz;
+			}
+		}
+		if (sec->PortalBlocksMovement(sector_t::floor))
+		{ // Use sector's floor
+			if (resultffloor) *resultffloor = NULL;
+			if (resultsec) *resultsec = sec;
+			return sec->floorplane.ZatPoint(x, y);
+		}
+		else
+		{
+			FDisplacement &disp = sec->FloorDisplacement();
+			x += disp.pos.x;
+			y += disp.pos.y;
+			sec = P_PointInSector(x, y);
+		}
+	}
+}
+
 //===========================================================================
 //
 // Calculates the height of a sector plane, respecting portal offsets
@@ -1163,3 +1231,43 @@ int side_t::GetLightLevel (bool foggy, int baselight, bool is3dlight, int *pfake
 	return baselight;
 }
 
+#include "c_dispatch.h"
+#include "d_player.h"
+
+CCMD(highestceiling)
+{
+	sector_t *sec;
+	fixed_t h = players[consoleplayer].mo->Sector->HighestCeilingAt(players[consoleplayer].mo, &sec);
+	Printf("Check at position %f,%f, height = %f, srcsector = %d dstsector = %d, srcgroup = %d, dstgroup = %d\n",
+		players[consoleplayer].mo->X() / 65536., players[consoleplayer].mo->Y() / 65536., h / 65536.,
+		players[consoleplayer].mo->Sector->sectornum, sec->sectornum, players[consoleplayer].mo->Sector->PortalGroup, sec->PortalGroup);
+}
+
+CCMD(lowestfloor)
+{
+	sector_t *sec;
+	fixed_t h = players[consoleplayer].mo->Sector->LowestFloorAt(players[consoleplayer].mo, &sec);
+	Printf("Check at position %f,%f, height = %f, srcsector = %d dstsector = %d, srcgroup = %d, dstgroup = %d\n",
+		players[consoleplayer].mo->X() / 65536., players[consoleplayer].mo->Y() / 65536., h / 65536.,
+		players[consoleplayer].mo->Sector->sectornum, sec->sectornum, players[consoleplayer].mo->Sector->PortalGroup, sec->PortalGroup);
+}
+
+CCMD(nexthighestceiling)
+{
+	sector_t *sec;
+	F3DFloor *ff;
+	fixed_t h = players[consoleplayer].mo->Sector->NextHighestCeilingAt(players[consoleplayer].mo, players[consoleplayer].mo->Top(), &sec, &ff);
+	Printf("Check at position %f,%f, height = %f, srcsector = %d dstsector = %d, srcgroup = %d, dstgroup = %d, 3dfloor = %d\n",
+		players[consoleplayer].mo->X() / 65536., players[consoleplayer].mo->Y() / 65536., h / 65536.,
+		players[consoleplayer].mo->Sector->sectornum, sec->sectornum, players[consoleplayer].mo->Sector->PortalGroup, sec->PortalGroup, !!ff);
+}
+
+CCMD(nextlowestfloor)
+{
+	sector_t *sec;
+	F3DFloor *ff;
+	fixed_t h = players[consoleplayer].mo->Sector->NextLowestFloorAt(players[consoleplayer].mo, players[consoleplayer].mo->Z(), &sec, &ff);
+	Printf("Check at position %f,%f, height = %f, srcsector = %d dstsector = %d, srcgroup = %d, dstgroup = %d, 3dfloor = %d\n",
+		players[consoleplayer].mo->X() / 65536., players[consoleplayer].mo->Y() / 65536., h / 65536.,
+		players[consoleplayer].mo->Sector->sectornum, sec->sectornum, players[consoleplayer].mo->Sector->PortalGroup, sec->PortalGroup, !!ff);
+}
diff --git a/src/r_defs.h b/src/r_defs.h
index 15b7337cd..739151c06 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -764,6 +764,19 @@ struct sector_t
 		return LowestFloorAt(a->X(), a->Y(), resultsec);
 	}
 
+	fixed_t NextHighestCeilingAt(fixed_t x, fixed_t y, fixed_t z, sector_t **resultsec = NULL, F3DFloor **resultffloor = NULL);
+	fixed_t NextLowestFloorAt(fixed_t x, fixed_t y, fixed_t z, sector_t **resultsec = NULL, F3DFloor **resultffloor = NULL);
+
+	fixed_t NextHighestCeilingAt(AActor *a, fixed_t z, sector_t **resultsec = NULL, F3DFloor **resultffloor = NULL)
+	{
+		return NextHighestCeilingAt(a->X(), a->Y(), z, resultsec, resultffloor);
+	}
+
+	fixed_t NextLowestFloorAt(AActor *a, fixed_t z, sector_t **resultsec = NULL, F3DFloor **resultffloor = NULL)
+	{
+		return NextLowestFloorAt(a->X(), a->Y(), z, resultsec, resultffloor);
+	}
+
 	// ... for ceilings
 	fixed_t CeilingAtPoint(fixed_t x, fixed_t y, int refgroup) const
 	{