icl::markers::BCHCoder Class Reference

Main class for BCH encoding/decoding. More...

#include <BCHCode.h>

Inheritance diagram for icl::markers::BCHCoder:

Public Member Functions
	BCHCoder ()
	Default constructor. More...
	~BCHCoder ()
	Destructor. More...
DecodedBCHCode	decode (const BCHCode &code)
DecodedBCHCode	decode (const icl8u data[36])
	decodes given (correctly oriented) byte image patch More...
DecodedBCHCode	decode (const core::Img8u &image, bool useROI=true)
	decodes given (correctly oriented) core::Img8u (optionally using its ROI or not) More...
DecodedBCHCode2D	decode2D (const core::Img8u &image, int maxID=4095, bool useROI=true)
	decodes given core::Img8u (optionally using its ROI or not) More...

Static Public Member Functions
static BCHCode	encode (int idx)
	encodes a given index in range [0,4095] to a BCHBinary code More...
static core::Img8u	createMarkerImage (int idx, int border=2, const utils::Size &resultSize=utils::Size::null)
	creates an image that show a given bch marker More...
static BCHCode	rotateCode (const BCHCode &in)
	interpretes the given 36Bit as 6x6 image and rotates it by clock wise by 90 degree More...

Private Attributes
Impl *	impl
	internal implementation structure More...

Additional Inherited Members
Protected Member Functions inherited from icl::utils::Uncopyable
	Uncopyable ()
	Empty base constructor. More...

Detailed Description

Main class for BCH encoding/decoding.

Due to some internal buffers, this must be implemented as a class

Constructor & Destructor Documentation

BCHCoder()

icl::markers::BCHCoder::BCHCoder

(

)

Default constructor.

~BCHCoder()

icl::markers::BCHCoder::~BCHCoder

(

)

Destructor.

Member Function Documentation

createMarkerImage()

static core::Img8u icl::markers::BCHCoder::createMarkerImage ( int  idx, int  border = 2, const utils::Size &  resultSize = utils::Size::null  )

static

creates an image that show a given bch marker

Parameters

idx	which marker
border	amount of border pixels (here, we use the unit of marker pixels, the maker code is always 6x6 marker pixels)
resultSize	first a (2*border+6)x(2*border+6) image of the marker is created. Then it is upscaled to the given utils::Size using nearest neighbour interpolation. If resultSize is null, the (2*border+6)x(2*border+6) image is returned directly without upscaling

decode() [1/3]

DecodedBCHCode icl::markers::BCHCoder::decode

(

const BCHCode &

code

)

We use an error correcting 36Bit BCH code that carries 12 bit of information (i.e. each possible code is associated with a unique index (0 <= index <= 4095). The code provides automatic error correction for inputs that have not more than 4 errors. Its minimal hammin distance is 8. The higher the code indices, the lower their hamming distance:

• min hamming distance > 8 : all
• min hamming distance > 9 : IDs 0-63
• min hamming distance > 10 : IDs 0-15
• min hamming distance > 13 : IDs 0-3
• min hamming distance > 16 : IDs 0-1

Benchmarks:

Decoding works quite fast, however the decoder works slightly slower if errors have to be corrected. We benchmarked the BCHDecoder on an Intel(R) Xeon(R) CPU E5530 running at 2.40GHz, on 32Bit Ubuntu Linux. Decoding without errors (2ns) Decoding with 1,2 and 3 errors (3ns) Decoding with 4 errors (4ns)

Implementing the Configurable Interface

We used the code implemented by Robert Morelos-Zaragoza. You can find his copyright note in the corresponding .cpp file

decode() [2/3]

DecodedBCHCode icl::markers::BCHCoder::decode

(

const icl8u

data[36]

)

decodes given (correctly oriented) byte image patch

decode() [3/3]

DecodedBCHCode icl::markers::BCHCoder::decode	(	const core::Img8u &	image,
		bool	useROI = true
	)

decodes given (correctly oriented) core::Img8u (optionally using its ROI or not)

decode2D()

DecodedBCHCode2D icl::markers::BCHCoder::decode2D	(	const core::Img8u &	image,
		int	maxID = 4095,
		bool	useROI = true
	)

decodes given core::Img8u (optionally using its ROI or not)

Internally, this methods checks for all 4 possible image rotations and returns the most plausible result.

Rotated Hamming Distances

If we allow rotations, the expected inter-marker hamming distances gets smaller.

• min hamming distance > 1: all
• min hamming distance > 2: 3080
• min hamming distance > 4: 2492
• min hamming distance > 5: 482
• min hamming distance > 8: 18
• min hamming distance > 10: 10
• min hamming distance > 11: 4

please note that it's best to use the first N IDs if you want to use N markers

encode()

static BCHCode icl::markers::BCHCoder::encode ( int  idx )

static

encodes a given index in range [0,4095] to a BCHBinary code

rotateCode()

static BCHCode icl::markers::BCHCoder::rotateCode ( const BCHCode &  in )

static

interpretes the given 36Bit as 6x6 image and rotates it by clock wise by 90 degree

Member Data Documentation

impl

Impl* icl::markers::BCHCoder::impl

private

internal implementation structure

implementation pointer

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The documentation for this class was generated from the following file:

• /Users/alneuman/vm/icl/ICLMarkers/src/ICLMarkers/BCHCode.h