Index: src/uk/me/parabola/imgfmt/app/dem/DEMSection.java
===================================================================
--- src/uk/me/parabola/imgfmt/app/dem/DEMSection.java	(revision 4104)
+++ src/uk/me/parabola/imgfmt/app/dem/DEMSection.java	(working copy)
@@ -126,8 +126,7 @@
 				tiles.add(tile);
 				if (tile.getEncodingType() != 0)
 					hasExtra = true;
-				int bsLen = tile.getBitStreamLen();
-				if (bsLen > 0) {
+				if (tile.validHeights()) {
 					if (tile.getBaseHeight() < minBaseHeight)
 						minBaseHeight = tile.getBaseHeight();
 					if (tile.getBaseHeight() > maxBaseHeight)
@@ -136,8 +135,8 @@
 						maxHeight = tile.getMaxHeight();
 					if (tile.getMaxDeltaHeight() > maxDeltaHeight)
 						maxDeltaHeight = tile.getMaxDeltaHeight();
-					dataLen += bsLen;
 				}
+				dataLen += tile.getBitStreamLen();
 			}
 			if (lastLevel) {
 				hgtConverter.freeMem();
Index: src/uk/me/parabola/imgfmt/app/dem/DEMTile.java
===================================================================
--- src/uk/me/parabola/imgfmt/app/dem/DEMTile.java	(revision 4104)
+++ src/uk/me/parabola/imgfmt/app/dem/DEMTile.java	(working copy)
@@ -43,6 +43,7 @@
 	private final int baseHeight;		// base or minimum height in this tile 
 	private final int maxDeltaHeight;	// delta between max height and base height
 	private final byte encodingType;  	// determines how the highest values are displayed 
+	private final boolean hasData;		// not all voids
 
 	private int bitPos;
 	private byte currByte;
@@ -94,18 +95,18 @@
 		}
 		if (min == Integer.MAX_VALUE) {
 			// all values are invalid 
+			hasData = false;
 			encodingType = 2;
 			min = 0;
-			max = 1;
-			// seems we still need a bit stream in this case
-			realHeights = new short[width * height];
-			Arrays.fill(realHeights, HGTReader.UNDEF);
+			max = 0;
 		} else if (countInvalid > 0) {
 			// some values are invalid
+			hasData = true;
 			encodingType = 2; // don't display highest value 
 			max++;
 		} else {
 			// all height values are valid
+			hasData = true;
 			encodingType = 0;
 		}
 
@@ -117,6 +118,10 @@
 		createBitStream(realHeights);
 	}
 	
+	public boolean validHeights() {
+		return hasData;
+	}
+
 	public int getBaseHeight() {
 		return baseHeight;
 	}