Braille Typesetting in 3-D Computer-Aided Design and Manufacturing

Stewart Dickson,
127 Claremont Road

mathart(a)emsh.calarts.edu

Background

This work is a means of granting accessibility to 3-D computer 'visualization' of science and mathematics to the visually impaired.

This is the documentation of a first attempt to apply tactile captions to a 3-D model in-the-round in a 3-D Computer-Aided Design system. The goal is to do interactive Braille typesetting in a 3-D Computer-Aided Design system, apply lines of text to arbitrary curved geometry and to render the annotated model physical in an Automated Fabrication system.

Current Development

The source of the digital Braille font was DotsPlus for Macintosh/Microsoft Word, developed and posted on-line by the Science Access Project, Department of Physics, Oregon State University.

Figure 1 The DotsPlus Braille Font (Feb. 20, 1998) rendered in PostScript.

The page, above, translates from DotsPlus Braille as:

!"#$%&'()*+,-./0123456789:;<=>?@
ABCDEFGHIJKLMNOPQRSTUVWXYZ
[\]^_`abcdefghijklmnopqrstuvwxyz{|}

Adobe Illustrator for Macintosh is capable of converting a PostScript outline font to CAD geometry.

Note that the DotsPlus font is a combination of dots-composed characters and solid, raised-line tactile symbols.

Figure 2 The Non-Symbol Portion of the DotsPlus Braille Font

The dots-composed characters were separated from the raised-line tactile symbols and treated separately.

A piece of geometry representing a single, 3-D Dot was modeled in a CAD system. The Dot is a truncated octagonal pyramid 0.046" high (Z-axis). The CAD geometry representing the Dots-only portion of the font consisted of a series of circles in the X-Y plane (Z=0). For each circle in the Dots-only font, a copy of the 3-D Dot object was positioned at the X-Y center of the circle, such that the 3-D dot extends +-0.023" forward and behind the Dots-only font. This was done procedurally using software written by the author.

Figure 3 The Letter 'Z', constructed by positioning a CAD 3-D Dot to the elements of a digital outline font.

The symbol portion of the font was constructed in 3-D by extruding the font outline 0.023" forward and backward from the font outline (at Z=0).

The planar faces of the symbols were tiled with polygons to allow them to warp onto curved surfaces.

Figures 4 and 5 show computer renderings of the complete 3-D CAD model (smooth-shaded and in wireframe, respectively) as prepared for Automated Fabrication.

For the test-build, a cylinder was constructed, 0.125" thick, 2.889" high by 3.6" in diameter. The entire DotsPlus 3-D font was warped onto the cylinder.

The CAD object was output in ABS thermoplastic using a Stratasys Fused Deposition Modeling (FDM) machine at the Partnership for Research in Stereo Modeling (PRISM Center) Arizona State University.

Figures 6 through 8 are photographs showing the object which resulted from the Fused Deposition Modeling of the CAD model.

Because the ABS material is transparent, the object is difficult to examine visually. For a sighted person to examine the object, it was necessary to mark the raised features with a felt-tipped marker to render them visible.

It can bee seen in the object, that the Fused Deposition Modeler had difficulty rendering the extended vertical bar features of the symbols, '!' (exclamation), ',' (comma), '.' (period) and ';' (semicolon). This might not be a problem for another 3-D printing technology. And, there might be a way to redesign the geometry of these symbols to improve their rendition in Fused Deposition Modeling.

Note that the modeled Dot object (Figure 3) is pyramidal in shape -- it is wider at the base than at the apex. The Symbol objects were all orthographically extruded from their cross-section. Virtually every Dot in the font was rendered correctly by the FDM machine. Widening the bases of the bar features of the Symbol characters may improve their rendition in Automated Fabrication.

Future Development

The text composition was unmodified from that derived by extracting outlines from the PostScript font. A computer user interface will be built to compose a line of text in the Braille as 3-D geometry, given a typed line of ASCII characters. (See DotsPlus 3D for Maya)

The composed text was applied to a piece of geometry (a flattened square prism, tiled with polygons on its face), and the resulting composite object was geometrically warped into a cylinder, mathematically, using a program written by the author. A computer user interface will be built to position a block of Braille text geometry onto an arbitrary piece of mathematical surface geometry.

To date, the author has developed a facility for treating an Open Inventor SoQuadMesh geometric shape node type as a parametric surface, and mapping another object (such as a line of 3-D text) onto that surface, within the domain of its parametric space.

The Open Inventor SoQuadMesh node contains restrictions to ensure that it is a topologically rectangular polygon mesh, such that 'parameterization' is an easy matter.

This simplistic view, exploited in the SoQuadMesh node, is usually not possible in objects derived from scientific or mathematical visualization. Particularly, polygon meshes derived from implicitly solved functions and iso-surfaces are notoriously unorganized.

The author plans to create a 3-D computer interface which will allow the user to:

• Organize a polygon data set into a strictly manifold, closed surface, suitable for automated fabrication;
• Draw onto the surface of the polygon data set a topologically rectangular region, which will become a 'parameterized region' of the surface;
• Map an object (such as a block of 3-D text) into the arbitrary parametric region of the surface and interactively position the block of text within the region.