diff --git a/src/map/IMG/rgnfile.cpp b/src/map/IMG/rgnfile.cpp
index a2b6cef1..e8d83cd7 100644
--- a/src/map/IMG/rgnfile.cpp
+++ b/src/map/IMG/rgnfile.cpp
@@ -1,10 +1,26 @@
-#include "trefile.h"
+#include "common/rectc.h"
 #include "units.h"
 #include "lblfile.h"
 #include "netfile.h"
 #include "rgnfile.h"
 
 
+static int bitSize(quint8 baseSize, bool variableSign, bool extraBit)
+{
+	int bits = 2;
+	if (baseSize <= 9)
+		bits += baseSize;
+	else
+		bits += 2 * baseSize - 9;
+
+	if (variableSign)
+		bits++;
+	if (extraBit)
+		bits++;
+
+	return bits;
+}
+
 bool RGNFile::BitStream::read(int bits, quint32 &val)
 {
 	val = 0;
@@ -34,29 +50,49 @@ bool RGNFile::BitStream::read(int bits, quint32 &val)
 	return true;
 }
 
-bool RGNFile::BitStream::readDelta(int bits, int sign, bool extraBit,
+bool RGNFile::BitStream::flush()
+{
+	while (_length--)
+		if (!_file.readByte(_hdl, _data))
+			return false;
+	return true;
+}
+
+RGNFile::DeltaStream::DeltaStream(const SubFile &file, Handle &hdl,
+  quint32 length, quint8 info, bool extraBit, bool extended)
+  : BitStream(file, hdl, length), _lonBits(0), _latBits(0)
+{
+	_extraBit = extraBit ? 1 : 0;
+	if (!(sign(_lonSign) && sign(_latSign)))
+		return;
+	if (extended) {
+		quint32 b;
+		if (!read(1, b))
+			return;
+	}
+	_lonBits = bitSize(info & 0x0F, !_lonSign, extraBit);
+	_latBits = bitSize(info >> 4, !_latSign, false);
+}
+
+bool RGNFile::DeltaStream::readDelta(int bits, int sign, int extraBit,
   qint32 &delta)
 {
 	quint32 value;
-	int bo = 0;
 
 	if (!read(bits, value))
 		return false;
 
-	if (extraBit) {
-		value>>=1;
-		bo = 1;
-	}
+	value >>= extraBit;
 
 	if (!sign) {
-		qint32 signMask = 1 << (bits - bo - 1);
+		qint32 signMask = 1 << (bits - extraBit - 1);
 		if (value & signMask) {
 			qint32 comp = value ^ signMask;
 			if (comp)
 				delta = comp - signMask;
 			else {
 				qint32 other;
-				if (!readDelta(bits - bo, sign, false, other))
+				if (!readDelta(bits - extraBit, sign, false, other))
 					return false;
 				if (other < 0)
 					delta = 1 - signMask + other;
@@ -73,7 +109,7 @@ bool RGNFile::BitStream::readDelta(int bits, int sign, bool extraBit,
 	return true;
 }
 
-bool RGNFile::BitStream::sign(int &val)
+bool RGNFile::DeltaStream::sign(int &val)
 {
 	quint32 bit;
 	val = 0;
@@ -89,14 +125,6 @@ bool RGNFile::BitStream::sign(int &val)
 	return true;
 }
 
-bool RGNFile::BitStream::finish()
-{
-	while (_length--)
-		if (!_file.readByte(_hdl, _data))
-			return false;
-	return true;
-}
-
 
 bool RGNFile::init()
 {
@@ -132,22 +160,6 @@ bool RGNFile::init()
 	return true;
 }
 
-static int bitSize(quint8 baseSize, bool variableSign, bool extraBit)
-{
-	int bits = 2;
-	if (baseSize <= 9)
-		bits += baseSize;
-	else
-		bits += 2 * baseSize - 9;
-
-	if (variableSign)
-		bits++;
-	if (extraBit)
-		bits++;
-
-	return bits;
-}
-
 bool RGNFile::polyObjects(const RectC &rect, Handle &hdl, const SubDiv *subdiv,
   const Segment &segment, LBLFile *lbl, Handle &lblHdl, NETFile *net,
   Handle &netHdl, QList<IMG::Poly> *polys) const
@@ -190,19 +202,14 @@ bool RGNFile::polyObjects(const RectC &rect, Handle &hdl, const SubDiv *subdiv,
 		br = br.united(c);
 		poly.points.append(QPointF(c.lon(), c.lat()));
 
-		BitStream bs(*this, hdl, len);
-		int lonSign, latSign;
-		if (!bs.sign(lonSign) || !bs.sign(latSign))
+		DeltaStream stream(*this, hdl, len, bitstreamInfo, labelPtr & 0x400000,
+		  false);
+		if (!stream.isValid())
 			return false;
-		bool extraBit = labelPtr & 0x400000;
-		int lonBits = bitSize(bitstreamInfo & 0x0F, !lonSign, extraBit);
-		int latBits = bitSize(bitstreamInfo >> 4, !latSign, false);
-
-		while (bs.hasNext(lonBits + latBits)) {
+		while (stream.hasNext()) {
 			qint32 lonDelta, latDelta;
 
-			if (!(bs.readDelta(lonBits, lonSign, extraBit, lonDelta)
-			  &&  bs.readDelta(latBits, latSign, false, latDelta)))
+			if (!(stream.readNext(lonDelta, latDelta)))
 				return false;
 
 			pos.rx() += lonDelta<<(24-subdiv->bits());
@@ -212,7 +219,7 @@ bool RGNFile::polyObjects(const RectC &rect, Handle &hdl, const SubDiv *subdiv,
 			poly.points.append(QPointF(c.lon(), c.lat()));
 			br = br.united(c);
 		}
-		if (!bs.finish())
+		if (!stream.flush())
 			return false;
 
 		if (!rect.intersects(br))
@@ -268,20 +275,13 @@ bool RGNFile::extPolyObjects(const RectC &rect, Handle &hdl,
 		br = br.united(c);
 		poly.points.append(QPointF(c.lon(), c.lat()));
 
-		BitStream bs(*this, hdl, len - 1);
-		int lonSign, latSign;
-		if (!bs.sign(lonSign) || !bs.sign(latSign))
+		DeltaStream stream(*this, hdl, len - 1, bitstreamInfo, false, true);
+		if (!stream.isValid())
 			return false;
-		quint32 extraBit;
-		bs.read(1, extraBit);
-		int lonBits = bitSize(bitstreamInfo & 0x0F, !lonSign, extraBit);
-		int latBits = bitSize(bitstreamInfo >> 4, !latSign, extraBit);
-
-		while (bs.hasNext(lonBits + latBits)) {
+		while (stream.hasNext()) {
 			qint32 lonDelta, latDelta;
 
-			if (!(bs.readDelta(lonBits, lonSign, false, lonDelta)
-			  &&  bs.readDelta(latBits, latSign, false, latDelta)))
+			if (!(stream.readNext(lonDelta, latDelta)))
 				return false;
 
 			pos.rx() += lonDelta<<(24-subdiv->bits());
@@ -291,7 +291,7 @@ bool RGNFile::extPolyObjects(const RectC &rect, Handle &hdl,
 			poly.points.append(QPointF(c.lon(), c.lat()));
 			br = br.united(c);
 		}
-		if (!bs.finish())
+		if (!stream.flush())
 			return false;
 
 		if (subtype & 0x20) {
diff --git a/src/map/IMG/rgnfile.h b/src/map/IMG/rgnfile.h
index 2a38b5c7..12070ed9 100644
--- a/src/map/IMG/rgnfile.h
+++ b/src/map/IMG/rgnfile.h
@@ -60,11 +60,8 @@ private:
 		  : _file(file), _hdl(hdl), _length(length), _remaining(0) {}
 
 		bool read(int bits, quint32 &val);
-		bool readDelta(int bits, int sign, bool extraBit, qint32 &delta);
-		bool sign(int &val);
-		bool hasNext(int bits) const
-		  {return _length * 8 + _remaining >= (quint32)bits;}
-		bool finish();
+		bool flush();
+		quint64 bits() const {return _length * 8 + _remaining;}
 
 	private:
 		const SubFile &_file;
@@ -73,6 +70,26 @@ private:
 		quint8 _data;
 	};
 
+	class DeltaStream : public BitStream {
+	public:
+		DeltaStream(const SubFile &file, Handle &hdl, quint32 length,
+		  quint8 info, bool extraBit, bool extended);
+
+		bool isValid() const {return _lonBits && _latBits;}
+		bool hasNext() const
+		  {return bits() >= _lonBits + _latBits;}
+		bool readNext(qint32 &lonDelta, qint32 &latDelta)
+		  {return (readDelta(_lonBits, _lonSign, _extraBit, lonDelta)
+		  && readDelta(_latBits, _latSign, false, latDelta));}
+
+	private:
+		bool sign(int &val);
+		bool readDelta(int bits, int sign, int extraBit, qint32 &delta);
+
+		int _lonSign, _latSign, _extraBit;
+		quint32 _lonBits, _latBits;
+	};
+
 	bool init();
 
 	QVector<Segment> segments(Handle &hdl, const SubDiv *subdiv) const;