EP1869642A1

EP1869642A1 - Method and apparatus for encoding/decoding 3d mesh information

Info

Publication number: EP1869642A1
Application number: EP06747358A
Authority: EP
Inventors: Eun Young Chang; Nam Ho Hur; Soo In Lee; Euee Seon Jang; Dai Yong Kim; Byeong Wook Min; Sun Young Lee
Original assignee: Electronics and Telecommunications Research Institute ETRI; Industry University Cooperation Foundation IUCF HYU; Industry University Cooperation Foundation of Sogang University
Current assignee: Electronics and Telecommunications Research Institute ETRI; Industry University Cooperation Foundation IUCF HYU; Industry University Cooperation Foundation of Sogang University
Priority date: 2005-04-13
Filing date: 2006-04-13
Publication date: 2007-12-26
Also published as: EP1869642A4; WO2006110002A1

Abstract

A method and apparatus for encoding and decoding three-dimensional mesh information are provided. The method and apparatus separately encode/decode order information of elements, such as vertices and faces, of a three-dimensional mesh model (original model) in consideration of a change in an element order during encoding three-dimensional mesh information for the original model. The method for encoding three-dimensional mesh information includes the steps of: encoding the three-dimensional mesh information and outputting an encoded bit-stream; calculating order information of at least one element in an original model contained in the three-dimensional mesh information; encoding the element order information; and generating packets of the encoded bit-stream, wherein the encoded element order information is inserted into the packet.

Description

[DESCRIPTION]

[Invention Title]

METHOD AND APPARATUS FOR ENCODING/DECODING 3D MESH

INFORMATION

[Technical Field]

The present invention relates to encoding/decoding three-dimensional

mesh information, and more particularly, to a method and apparatus for

separately encoding/decoding order information of elements, such as vertices

and faces, of a three-dimensional mesh model (original model) in

consideration of a change in an element order during encoding three-

dimensional mesh information for the original model.

[Background Art]

Recent years have seen the beginning of widespread use of three-

dimensional graphics. However, applications of these complex graphics are

still limited because of the enormous amounts of information required for their

implementation. Three-dimensional mesh information representing a three-

dimensional model includes geometric information, inter-vertex connectivity

information, and property information, such as color, normal, and texture

coordinates. The geometric information includes information about three

coordinates of a floating point. The connectivity information is represented by an index list in which three or more vertices form one polygon. For

example, if a 32bit floating point is used to represent the geometric

information, 96 bits (12B) are needed to represent single geometric

information. That is, a 120KB memory is required when a three-dimensional

mesh model is represented by approximately ten thousand vertices having only

the geometric information. A 1.2MB memory is required when the model is

represented by a hundred thousand vertices. Further, since the connectivity

information can be overlapped twice or more, a massive memory is required to

store a three-dimensional model using a polygonal mesh.

Encoding is needed to solve the problem of the huge amount of

information. To this end, a three-dimensional mesh coding (3DMC) scheme

adopted as a standard of ISO/IEC (International Organization for

Standardization/International Electrotechnical Commission) in the field of

MPEG-4 (Moving Picture Expert Group)-SNHC (Synthetic and Natural

Hybrid Coding) improves transmission efficiency by encoding/decoding three-

dimensional mesh information represented by IndexedFaceSet (IFS) in a

Virtual Reality Modeling Language (VRML) file.

FIGS. Ia and Ib respectively illustrate conceptual configurations of

conventional 3DMC-based encoding and decoding devices. A 3DMC

encoding device 110 includes a topological surgery module 111 for

decomposing a three-dimensional mesh model (original model) into two- dimensional mesh structures, a geometric information encoding module 112, a

connectivity information encoding module 113, a property information

encoding module 114, and an entropy encoding module 115 for collectively

compressing encoding results from the encoding modules 112 to 114 to

generate a 3DMC bit-stream.

The 3DMC decoding device 120 includes an entropy decoding

module 121, a geometric information decoding module 122, a connectivity

information decoding module 123, a property information decoding module

124, and a topological synthesis module 125, in order to reconstruct three-

dimensional model data from the encoded 3DMC bit-stream.

The 3DMC encoding performed by the above-described 3DMC

encoding device 110 includes, as a primary characteristic, a topological

surgery operation performed by the topological surgery module 111 to

maximize a compression ratio. The topological surgery operation is

proposed by IBM cooperation and is a decomposition operation in which a

three-dimensional model is decomposed into two-dimensional mesh structures

by cutting the model along a given cutting edge on the assumption that a given

mesh is the same as a sphere in topological geometry. Such operation results

in a simple polygonal graph (e.g., a triangle tree (TT) having a binary tree

structure composed of a triangular strip) and a vertex graph (VG) representing

a path along which the mesh is cut, as an inter- vertex linked structure. However, the above-described topological surgery operation may

change the order of elements (e.g., vertices and faces) constituting an original

model. For this reason, editing cannot be performed in a unit of the elements,

such as vertices or faces, and animation effects based on the element order

cannot be applied.

[Disclosure]

[Technical Problem]

The present invention is directed to implementation of a method and

apparatus for separately encoding/decoding order information of elements in

an original model during encoding/decoding three-dimensional mesh

information.

The present invention is also directed to implementation of a method

and apparatus for encoding element orders, capable of reducing an encoding

bit rate by encoding element order information while sequentially

decrementing the number of bits for the codewords in a distinguishable unit.

[Technical Solution]

One aspect of the present invention provides a method for encoding

three-dimensional mesh information. The method includes the steps of

encoding the three-dimensional mesh information and outputting an encoded

bit-stream; calculating order information of at least one element in an original model contained in the three-dimensional mesh information; encoding the

element order information; and generating packets of the encoded bit-stream,

wherein the encoded element order information is inserted into the packets.

The element order information in the original model may be at least

one of vertex order information and face order information. The element

order information may be calculated in an IFS unit or a CC unit.

The step of encoding the element order information may include the

steps of: (i) setting an initial value of the codeword bit number used to encode

the element order information as ' ² ' (where, N is a total number

of the element order information); (ii) encoding a predetermined number of

element order information using the set bit number of codeword; (iii)

decrementing the codeword bit number by one; (iv) encoding some of the

remaining element order information which is not yet encoded using the

decremented bit number of codeword; and (v) repeating steps (iii) and (iv)

until all the element order information is encoded.

Another aspect of the present invention provides a method for

encoding element order information. The method includes the steps of:

calculating order information of at least one element in an original model

contained in three-dimensional mesh information; and encoding the element

order information. Still another aspect of the present invention provides a method for

decoding three-dimensional mesh information. The method includes the

steps of decoding three-dimensional mesh information packets to reconstruct

original model data; determining whether order information of elements in an

original model exists in a prescribed area of the packet; when it is determined

that the element order information exists, extracting the element order

information from the packet; decoding the extracted element order

information; and rearranging the reconstructed original model data based on

the decoded element order information.

Yet another aspect of the present invention provides a method for

decoding element order information in three-dimensional mesh information

packets. The method includes the steps of extracting element order

information from a prescribed area in the packet; and decoding the extracted

element order information.

Yet another aspect of the present invention provides an apparatus for

encoding three-dimensional mesh information. The apparatus includes

means for encoding three-dimensional mesh information to output an encoded

bit-stream; means for calculating order information of at least one element in

an original model contained in the three-dimensional mesh information; order

information encoding means for encoding the element order information; and means for generating packets of the encoded bit-stream, wherein the element

order information is inserted into the packet.

Yet another aspect of the present invention provides an apparatus for

decoding three-dimensional mesh information. The apparatus includes

means for decoding three-dimensional mesh information packets to

reconstruct original model data; order information decoding means for

decoding the element order information in the packet; and means for

rearranging the reconstructed original model data based on the decoded

element order information.

[Advantageous Effects]

With the method and apparatus for encoding and decoding the order

information of elements such as vertices or faces according to the present

invention as described above, it is possible to transmit the vertex/face order

information with a reduced encoding bit rate and without loss by encoding the

order information with the sequentially decremented number of codeword bits

allocated to the order information of each element in an original model,

thereby enabling functions of animating or editing a reconstructed model to be

supported.

[Description of Drawings] FIGS. Ia and Ib respectively illustrate conceptual configurations of

conventional 3DMC-based encoding and decoding devices;

FIG. 2a and 2b are schematic block diagrams illustrating a 3DMC

encoding device and a 3DMC decoding device according to an exemplary

embodiment of the present invention;

FIG. 3 is a flowchart illustrating a process of encoding three-

dimensional mesh information according to an exemplary embodiment of the

present invention;

FIG. 4 is a flowchart illustrating a process of decoding three-

dimensional mesh information according to an exemplary embodiment of the

present invention;

FIG. 5 is a flowchart illustrating a process of encoding element order

information in an IFS (IndexedFaceSet) unit according to an exemplary

embodiment of the present invention;

FIG. 6 is a flowchart illustrating a process of decoding element order

information in an IFS unit according to an exemplary embodiment of the

present invention;

FIGS. 7a and 7b illustrate an exemplary structure of a 3DMC packet

having vertex/face order information according to the present invention;

FIG. 8 illustrates a CC structure on IFS of a horse model; and FIGS. 9a, 9b and 9c illustrate an example of a header portion of

vertex/face order information according to the present invention.

[Mode for Invention]

Hereinafter, an exemplary embodiment of the present invention will

be described in detail. However, the present invention is not limited to the

exemplary embodiment disclosed below, but can be implemented in various

modified forms. Therefore, the present exemplary embodiment is provided

for a complete disclosure of the invention which is fully enabling to those of

ordinary skill in the art.

FIG. 2a and 2b are schematic block diagrams illustrating a 3DMC

encoding device 210 and a 3DMC decoding device 220 according to an

exemplary embodiment of the present invention. Referring to FIGS. 2a and

2b, the three-dimensional mesh information encoding device 210 includes a

topological surgery module 211, a geometric information encoding module

212, a connectivity information encoding module 213, a property information

encoding module 214, an entropy encoding module 215, and an element order

encoding module 216. That is, the encoding device 210 is characterized by

the element order encoding module 216 for separately encoding element order

information in a three-dimensional model, unlike the conventional 3DMC

encoding device 110 shown in FIG. Ia. Similarly, the three-dimensional mesh information decoding device

220 according to the present invention further includes an element order

decoding module 225 for decoding encoded element order information, and a

rearranging module 227 for rearranging reconstructed three-dimensional

model data based on the decoded element order information of the original

model, unlike the conventional 3DMC decoding device 120 shown in FIG. Ib.

In an exemplary embodiment, the information encoded/decoded by

the element order encoding module (216 of FIG. 2a) and the element order

decoding module (225 of FIG. 2b) is vertex order information. However, the

present invention is not limited to the vertex order information. In another

exemplary embodiment, face order information may be encoded/decoded

instead of the vertex order information. In yet another exemplary

embodiment, both the vertex order information and the face order information

may be encoded/decoded.

While the element order rearranging module 227 is shown in the FIG.

2b as operating prior to reconstruction of the three-dimensional model, the

present invention is not limited to this configuration. In another exemplary

embodiment, the rearranging module 227 may perform a post-process

following the three-dimensional model reconstruction.

FIG. 3 is a flowchart illustrating a process of encoding three-

dimensional mesh information according to an exemplary embodiment of the present invention. Referring to FIG. 3, three-dimensional mesh information

is encoded and an encoded bit-stream is outputted in step S310. According

to existing SNHC 3DMC encoding, the three-dimensional mesh information is

data created by decomposing a three-dimensional mesh model into two-

dimensional mesh structures (using topological surgery), and in an exemplary

embodiment, contains a vertex graph (VG) and a triangle tree (TT) graph

having a binary tree structure. However, the present invention focuses on

encoding the element order information that can be changed during an

encoding process, not encoding three-dimensional mesh information itself. It

will be appreciated by those skilled in the art that the present invention may be

applied to any encoding schemes changing an element order, as well as the

above-described SNHC 3DMC encoding scheme.

Order information (IFS unit or CC unit) of each element in the

original model contained in the three-dimensional mesh information is

calculated in step S320. In an exemplary embodiment, since an order of

elements such as the vertices and/or faces in the original model may be

changed by topological surgery in the 3DMC encoding process as described

above, it is necessary to calculate the original model-based order information

(IFS unit or CC unit) of each element contained in the three-dimensional mesh

information. In an exemplary embodiment, among the elements constituting

a three-dimensional model, order information of vertices may be calculated. In another exemplary embodiment, face order information may be calculated.

In yet another exemplary embodiment, both vertex and face order information

may be calculated.

In step S330, the calculated element order information is encoded.

According to an exemplary embodiment, the element order information is

encoded to reduce an encoding bit rate while sequentially decrementing the bit

number of codewords allocated to the element order information in a

distinguishable unit. This will be described later with reference to FIG. 5.

In step S340, packets for the three-dimensional mesh information bit-

stream encoded in step S310 are generated. The element order information is

inserted into the packet.

Steps S310 to S340 are not necessarily performed in the above-

described order. It will be appreciated by those skilled in the art that, in

actual implementation, the steps may be performed in changed order and/or in

parallel, wherein the result of performing one step should not affect the result

of performing the other step.

FIG. 4 is a flowchart illustrating a process of decoding a three-

dimensional mesh information packet according to an exemplary embodiment

of the present invention. The three-dimensional mesh information packets

are decoded in step S410. The decoding performed here is known in the art

and a detailed description thereof will be omitted herein. In step S420, a determination is made as to whether the element order

information for an original model is contained in a prescribed area (e.g.,

header area) of the three-dimensional mesh information packet. If the

element order information is not contained, the decoding process ends.

If it is determined in step S420 that the element order information is

contained in the received packets, the element order information is extracted in

step S430 and the extracted element order information is decoded in step S440.

In step S450, a reconstructed model is rearranged in the same order as the

original model using the decoded element order information. Steps S410 to

S450 are not necessarily performed in the above-described order. It will be

easily appreciated by those skilled in the art that the order may be changed.

For example, in another exemplary embodiment, the element order

information determining step S430, the element order information extracting

step S440, and the decoding step S450 may be performed prior to the 3DMC

decoding step S410.

As described above, the present invention is further characterized by

reducing the encoding bit rate by sequentially decrementing the bit number of

codewords allocated to the element order information, such as a vertex order

and a face order, in a distinguishable unit in encoding the element order

information. To assist in understanding the encoding of the element order

information according to the present invention, the codewords allocated upon encoding the vertex order information in an IFS unit according to the present

invention are shown in Table 1.

Table 1

As shown from Table 1 , when the total number of the vertices in the

original model is 6, 3 bits are required to represent the order information of

each vertex. The order information "0" and "2" are encoded with codewords

"000" and "010," respectively.

Four order information, i.e., "1," "5," "4" and "3" remain after "0"

and "2" are encoded. Two bits can be used to identify the four order

information. Among the remaining order information, a 2-bit codeword

value allocated to the first two order information "1" and "5" may be

determined by any algorithm. In this example, "00" and "11" are allocated in

an ascending order. The codeword values are not necessarily allocated in the ascending order, but may be allocated using several methods including a

descending order.

Next, the remaining order information after encoding "1" and "5" are

"4" and "3," which can be identified by one bit. Thus, a codeword "1" is

allocated to "4" in an ascending order. The last order information "3" is not

substantially transmitted since it can be predicted at a receiving side.

However, the last order information may be encoded with "0" and transmitted

for determining whether an error occurs over a network.

While, in the example shown in Table 1 , two of the six vertices are

encoded into three bits, two other vertices into two bits, and one vertex (two

vertices) into one bit, four of the six vertices may be encoded into three bits

and two vertices into two bits in another embodiment. Others combinations

may also be allowed.

FIG. 5 is a flowchart illustrating a process of encoding element order

information in an IFS (IndexedFaceSet) unit according to an exemplary

embodiment of the present invention. While, in FIG. 5, the process of

encoding the vertex order information (steps 510a to 560a) and the process of

encoding the face order information (steps 510b to 560b) are shown as being

both performed, the present invention is not limited to such an exemplary

embodiment as described previously. The vertex order information, the face order information, or both the vertex and face order information may be

selectively encoded.

First, an initial value of the codeword bit number to be allocated (bit

per vertices information: bpvi) for the vertex order information is set as

(where, nV denotes a total number of vertices constituting

the original model) (step 510a). If the total vertex number nV is 6, the bpvi

value will equal 3.

In an exemplary embodiment, the number of the vertices to be

encoded with the bpvi bit number, Coding_Vertices, is calculated by Equation

1 (step 520a).

Equation 1

Coding_Vertices = nV - 2^(bpvM)

In the above example in which the total vertex number is 6, the

calculated Coding_Vertices value becomes 2. The calculated Coding_Vertices

number of vertex order information is then encoded using the bpvi -bit

codeword (step 530a). Thus, in the example, two vertex order information

will be encoded using three-bit codewords.

The scheme for calculating Coding Vertices is only illustrative, and

the present invention is not limited to such a calculating scheme.

Alternatively, the Coding_Vertices value may be determined as 7> ^vmA\ The total vertex number nV is then decremented by the encoded

vertex number, CodingJVertices (step 540a), and a determination is made as to

whether a total number of remaining vertices, nV, is one (step 550a).

Otherwise, the codeword bit number bpvi is decremented by one (step S 560a)

and then the above-described steps 520a to 560a are repeated to encode order

information of all the vertices.

Meanwhile, in steps 510b to 560b, an nF number of face order

information is encoded in the same manner as in the above-described steps of

encoding the vertex order information (510a to 560a). A detailed description

of steps 510b to 560b will be omitted.

Thus, according to the present invention, it is possible to reduce the

encoding bit rate by encoding the vertex/face order information while

sequentially decrementing the codeword bit number by one.

FIG. 6 is a flowchart illustrating a process of decoding element order

information in an IFS unit according to an exemplary embodiment of the

present invention.

First, the initial value of the codeword bit number, "bpvi (bit per

vertices information)" allocated to the encoded vertex order information is

calculated by Equation 2 (step 610a):

Equation 2 bpvi = ' '

The number of vertices to be decoded with the bpvi-bit codeword,

Decoding Vertices, is then calculated by Equation 3 (step 620a):

Equation 3

Decoding_Vertices = nV - 2^(bpvi"1}

This equation is only illustrative. In another exemplary embodiment,

the information about the number of the vertices to be decoded with the bpvi-

bit codeword, DecodingJVertices, may be contained in the encoded vertex

order information.

Next, the Decoding_Vertices number of bpvi-bit codewords are

sequentially read from the encoded vertex order information, and the vertex

order information is decoded from the codewords (step 630a). Then, the total

vertex number nV is decremented by the decoded vertex number

DecodingJVertices, and a determination is made as to whether a remaining

vertex total number nV is one (step S650a). Otherwise, the bit number bpvi

of the codeword to be read is decremented by one (step S660a) and the above-

described steps 620a to 660a are repeated to decode the order information of

all the vertices.

Meanwhile, steps 610b to 660b decode an nF number of face order

information in the same manner as in the above-described steps 610a to 660a of decoding the vertex order information, and a detailed description of steps

610b to 660b will be omitted.

The process of encoding/decoding the element order information

when the element order information is calculated in the IFS unit has been

described. FIG. 7a shows an example in which element order information is

inserted per IFS.

Meanwhile, according to another exemplary embodiment of the

present invention, element order information may be calculated in a connected

component (CC) unit. FIG. 7b shows an example in which element order

information is inserted per CC. When element order information is inserted

per CC, "VO" and "FO" respectively include order information of the vertices

and faces constituting each CC. However, a flag indicating whether the vertex

order information and/or the face order information is included is not need be

included per CC.

While, in the above example, one bit is allocated to the flag indicating

whether the vertex order information and the face order information is

included, in another example, a 2-bit "vertex_face_order_flag" flag may be

used to represent the following:

Table 2

As described above, the element order information may be inserted

per IFS or per CC. When the element order information is inserted per CC,

an element order information value calculated in the IFS unit may be simply

inserted per CC. Alternatively, the element order information value

calculated in the IFS unit may be converted to an element order information

value calculated in the CC unit and then inserted per CC.

For example, when a model including 900 vertices is composed of

three CCs each including 300 vertices, the use of the IFS unit allows the

element order information having order information values from 0 to 899 to be

encoded while the use of the CC unit allows for conversion into order

information values from 0 to 299 for representation. Thus, the use of the CC

unit enables the element order information values to be encoded using fewer

bits than use of the IFS unit. For example, in case of the model consisting of

900 vertices, it is assumed that the first CC of the model is composed of 300

vertices having order information values from 0 to 299, the second CC is

composed of 300 vertices having order information values from 300 to 599, and the third CC is composed of 300 vertices having order information values

from 600 to 899. For the first CC, since the order information values

represented by 0 to 299 are unchanged after conversion into the CC unit, these

values are encoded through the process of FIG. 5. For the second CC, the

order information values in the IFS unit represented by 300 to 599 are

converted to the order information values in the CC unit represented by 0 to

299. The conversion is made by simply subtracting 300 from each element

order information value since, in the first CC, the 300 vertices are encoded.

For the third CC, the order information having values of 600 to 899 can be

converted to the order information value in the CC unit having values of 0 to

299 by subtracting 600 since the order information is encoded by 300 order

information in the first CC and the second CC.

Besides, CC composition on the IFS may have several structures.

That is, there may be a model in which each CC is not sequentially connected.

As one example, a CC composition of a horse model is shown in FIG. 8.

Since the horse model is composed of 11,135 vertices, it has element order

information from 0 to 11,134 on the IFS. The IFS is composed of three CCs,

in which the first CC is composed of 10,811 vertices having values from 0 to

11,134, the second CC is composed of 162 vertices having values from 3,200

to 3,523, and the third CC is composed of 162 vertices having values from

3,299 to 3,460. These values may be represented in the CC unit so that the first CC has a value from O to 10,810 and the second and third CCs have

values from 0 to 161. However, since the order information in this model

exhibits an overlapping structure when converted into the order information

value in the CC unit, simple addition or subtraction of any value provides no

solution. Accordingly, this problem can be solved by introducing an offset

value. The problem may be solved by providing the offset value to each

element order information, by providing the offset value in the CC unit, or by

providing the global CC structure information in the IFS to the header. There

are several other solutions as well.

For example, the horse model allows the offset values to be provided

in the CC unit by providing CC #1 = {0, 1, 2,..., 3199, 3524, 3525, ..., 11134},

CC #2 = {3200, 3201, ..., 3298, 3461, 3462,..., 3523} and CC #3 = {3299,

3300,..., 3460} , which are CC composition information, to the header portion,

which makes it possible to utilize advantages that can be obtained upon

encoding in the CC unit.

The process of encoding the vertex order information represented in

the CC unit is the same as the process of encoding the vertex order

information represented in the IFS unit except that an initial value of the

allocated codeword bit number (bit per vertices information: bpvi) of the

vertex order information is set as ' ' (where, nC-V is a total number of vertices constituting the i-th CC). The process of encoding

the nCiF number of face order information is also the same as the process of

encoding the face order information represented in the IFS unit except that an

initial value of the allocated codeword bit number (bit per faces information:

bpfi) of the face order information is set as ' ² * ' (where, TiC₁F

is a total number of faces constituting the i-th CC).

Thus, according to the present invention, it is possible to reduce the

encoding bit rate by converting the vertex/face order information represented

in the IFS unit into the vertex/face order information represented in the CC

unit and encoding the vertex/face order information represented in the CC unit

while sequentially decrementing the codeword bit number by one.

Further, the process of decoding the vertex order information

represented in the CC unit is the same as the process of decoding the vertex

order information represented in the IFS unit except that an initial value of the

allocated codeword bit number (bit per vertices information: bpvi) of the

vertex order information is set as ' ² ' (where, nC_tV is a total

number of vertices constituting the i-th CC). The process of decoding an

YiC₁F number of the face order information is the same as the process of

decoding the face order information represented in the IFS unit except that an

initial value of the allocated codeword bit number (bit per vertices information: bpvi) of the face order information is set as ' ^{2 2} '

(where, TiC₁F is a total number of vertices constituting the i-th CC).

However, a corresponding offset value in the header information may be

added to the decoded vertex/face order information values to reconstruct the

decoded vertex/face order information into the vertex/face order information

represented in the IFS unit.

FIGS. 9a, 9b and 9c illustrate one example of the structure of a header

portion indicating CC composition information on IFS according to the

present invention.

Referring to FIGS. 9a, 9b and 9c, the header information includes a

flag indicating whether offset information exists, the number of offsets applied

to each CC when the offset information exists, a real offset value, and the first

element order information (represented in the CC unit) to which each offset is

applied. The shown header structure is illustrative, and representation and

position of CC composition information in the header may be changed. For

example, among information about the real offset values provided to the

header portion, the second through last offset values, excluding the first offset

value, may be set to the value of a difference with a previous offset value. A determination as to whether to insert the element order information

per IFS or CC unit may be made based on model characteristics and an

encoding bit rate.

The present invention described above may be provided as a

computer program stored on one or more computer-readable medium. The

computer-readable medium may be a floppy disk, a hard disk, a CD ROM, a

flash memory card, a PROM, a RAM, a ROM, or a magnetic tape. Generally,

the computer program may be written in any programming language.

While the invention has been shown and described with reference to

certain exemplary embodiments thereof, it will be understood by those skilled

in the art that various changes in form and details may be made therein

without departing from the spirit and scope of the invention as defined by the

appended claims.

Claims

[CLAIMS][Claim 1 ]

1. A method for encoding three-dimensional mesh information,

comprising the steps of:

encoding the three-dimensional mesh information and outputting an

encoded bit-stream;

calculating order information of at least one element in an original

model contained in the three-dimensional mesh information;

encoding the element order information; and

generating packets of the encoded bit-stream, wherein the encoded

element order information is inserted into the packet.

[Claim 2]

The method for encoding three-dimensional mesh information

according to claim 1, wherein the element order information is at least one of

vertex order information and face order information.

[Claim 3] The method for encoding three-dimensional mesh information

according to claim 1, wherein the step of encoding the element order

information comprises the steps of:

(i) setting an initial value of a codeword bit number used to encode the

element order information as ' ² ' (where, N is a total number of

the element order information);

(ii) encoding a predetermined number of element order information

using the set bit number of codeword;

(iii) decrementing the codeword bit number by one;

(iv) encoding some of the remaining element order information which

is not yet encoded using the decremented bit number of codeword; and

(v) repeating steps (iii) and (iv) until all the element order information

is encoded.

[Claim 4]

The method for encoding three-dimensional mesh information

according to claim 1 , wherein the element order information is calculated in an

IFS (IndexedFaceSet) unit, and

the step of encoding the element order information comprises the steps

of: (i) converting the element order information calculated in the IFS unit

into element order information represented in a connected component (CC)

unit and an associated offset value;

i (ii) setting an initial value of a codeword bit number used to encode

the element order information as ^l (where, C₁TV is a total

number of the element order information in the i-th CC);

(iii) encoding a predetermined number of element order information

using the set bit number of codeword;

(iv) decrementing the codeword bit number by one;

(v) encoding some of the remaining element order information which

is not yet encoded using the decremented bit number of codeword; and

(vi) repeating steps (iv) and (v) until all the element order information

are encoded.

[Claim 5]

The method for encoding three-dimensional mesh information

according to claim 4, further comprising the step of storing, in a header of the

packet, a flag indicating that the element order information calculated in the

IFS unit is converted into element order information in the CC unit.

[Claim 6]

The method for encoding three-dimensional mesh information

according to claim 5, further comprising the step of storing the offset value in

the header of the packet.

[Claim 7]

A method for encoding element order information, comprising the

steps of:

calculating, in an IFS unit, order information of at least one element in

an original model contained in three-dimensional mesh information; and

encoding the element order information.

[Claim 8]

The method for encoding element order information according to

claim 7, further comprising the step of converting the element order

information value calculated in the IFS unit into an element order information

value in an CC unit and an associated offset value.

[Claim 9] A method for decoding three-dimensional mesh information,

comprising the steps of:

decoding a three-dimensional mesh information packet to reconstruct

original model data;

determining whether order information of elements in an original

model exists in a prescribed area of the packet;

when it is determined that the element order information exists,

extracting the element order information from the packet;

decoding the extracted element order information; and

rearranging the reconstructed original model data based on the

decoded element order information.

[Claim 10]

The method for decoding three-dimensional mesh information

according to claim 9, wherein the determination is based on a flag value

indicating whether the element order information exists in a prescribed area

within a header of the packet.

[Claim 11] The method for decoding three-dimensional mesh information

according to claim 9, wherein the step of determining whether the element

order information exists comprises determining whether at least one of vertex

order information and face order information exists.

[Claim 12]

The method for decoding three-dimensional mesh information

according to claim 9, wherein the step of decoding the element order

information comprises the steps of:

(i) setting an initial value of a bit number of codewords corresponding

to the element order information as ² (where, N is a total

number of the element order information);

(ii) reading a predetermined number of the codewords having the set

bit number and reconstructing corresponding element order information from

each of the read codewords;

(iii) decrementing the codeword bit number by one;

(iv) reading a predetermined number of the codewords having the

decremented bit number and reconstructing corresponding element order

information from each read codeword; and (v) repeating steps (iii) and (iv) until all the element order information

is reconstructed.

[Claim 13]

The method for decoding three-dimensional mesh information

according to claim 9, wherein the step of decoding the element order

information represented in a CC unit comprises the steps of:

(i) setting an initial value of a bit number of codewords corresponding

to the element order information as ' ^{to 2 i} (where, C₁N is a total

number of the element order information);

(ii) reading a predetermined number of the codewords having the set

bit number and reconstructing corresponding element order information from

each of the read codewords;

(iii) decrementing the codeword bit number by one;

(iv) reading a predetermined number of the codewords having the

decremented bit number and reconstructing corresponding element order

information from each read codeword;

(v) repeating steps (iii) and (iv) until all the element order information

is reconstructed; and (vi) adding a corresponding offset value stored in the packet to the

reconstructed element order information to reconstruct element order

information represented in an IFS unit.

[Claim 14]

A method for decoding element order information in a three-

dimensional mesh information, comprising the steps of:

extracting element order information from a prescribed area in the

three-dimensional mesh information packet; and

decoding the extracted element order information.

[Claim 15]

A method for decoding element order information in a three-

dimensional mesh information, comprising the steps of:

extracting the element order information from a prescribed area in the

three-dimensional mesh information packet;

decoding the extracted element order information; and

adding an offset value stored in the packet to the decoded element

order information value to reconstruct the element order information

represented in an IFS unit.

[Claim 16]

An apparatus for encoding three-dimensional mesh information,

comprising:

means for encoding the three-dimensional mesh information to output

an encoded bit-stream;

means for calculating order information of at least one element in an

original model contained in the three-dimensional mesh information;

order information encoding means for encoding the element order

information; and

means for generating packets of the encoded bit-stream, wherein the

element order information is inserted into the packet.

[Claim 17]

The apparatus for encoding three-dimensional mesh information

according to claim 16, further comprising means for decomposing the original

model into two-dimensional structures to generate three-dimensional mesh

information.

[Claim 18] The apparatus for encoding three-dimensional mesh information

according to claim 16, wherein the order information encoding means encodes

at least one of the vertex order information and face order information of the

three-dimensional mesh model.

[Claim 19]

An apparatus for decoding three-dimensional mesh information,

comprising:

means for decoding a three-dimensional mesh information packet to

reconstruct original model data;

order information decoding means for decoding element order

information in the packet; and

means for rearranging the reconstructed original model data based on

the decoded element order information.

[Claim 20]

A computer-readable recording medium having a computer program

recorded thereon to perform the method for encoding three-dimensional mesh

information according to any one of claims 1 to 6. [Claim 21]

A computer-readable recording medium having a computer program

recorded thereon to perform the method for decoding three-dimensional mesh

information according to any one of claims 9 to 13.