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# 3D Recognition From 2D Line Drawings by Using the Orthogonal Axes of 3D Space

IP.com Disclosure Number: IPCOM000100785D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 94K

IBM

## Related People

Minakata, H: AUTHOR [+2]

## Abstract

Disclosed is a program that reconstructs 3D objects from 2D line drawings. This program uses three heuristics that seem to be common to all people. As a result, 3D reconstruction is realized easily and fast. In addition, the substitution of an object coordinate system for an eye coordinate system facilitates the calculations.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

3D Recognition From 2D Line Drawings by Using the Orthogonal Axes of 3D Space

Disclosed is a program that reconstructs 3D objects from
2D line drawings. This program uses three heuristics that seem to be
common to all people. As a result, 3D reconstruction is realized
easily and fast. In addition, the substitution of an object
coordinate system for an eye coordinate system facilitates the
calculations.

The three heuristics are as follows.
1)   Existence of perpendicular axes that become object coordinate
axes.
2)   Definition of the vertical axis in 3D space by vertical lines in
2D drawings.
3)   Designation of the top of the picture as the eye position.

The reconstruction is done on these assumptions. A 2D sketch is
drawn by either parallel projection or cavalier projection. The
object need not necessarily be in the trihedral world, in which
exactly three planes are assumed to meet at every corner, but can
have an orthogonal symmetry axis. This means that this program can be
used even if the object is represented as a generalized cylinder.
However, an object coordinate center should be specified by the
operator, because the interpretation is not unique (Fig. 1).

The process consists of two parts: calculation of the
transformation parameters from an eye coordinate system to an object
coordinate system, and the recognition process for transforming 2D
projected line drawings to a 3D object by means of these
transformation parameters.

The first part is as follows. When a person draws a sketch, the
vertical axis seems to be fixed in 3D space. That is, the vertical
line on the 2D plane is supposed to be also vertical in 3D space.
First, the object coordinate axes are rotated B around the y-axis, as
the x-axis is parallel to the eye coordinate system, and then they
are rotated around the x-axis, as the eye direction is parallel to
the z-axis. In other words, the xy-plane in the eye coordinate system
is put together with the xy-plane in the object coordinate system.
The transformation equation is as follows:

(Image Omitted)

x' y' z' 1   =   x y z 1   R
cosB   0   -sinB   0      1    0     0    0 R =      0
1     0     0      0   cosA  sinA  0
sinB   0    cosB   0      0  -sinA  cosA  0
...