PRC (3D)

PRC (Product Representation Compact) is the 3D format Adobe made for 3D PDF, now the international standard ISO 14739-1. Acrobat and Adobe Reader show a PRC model inside a PDF, where it can be turned, zoomed and taken apart; CAD programs and PDF tools read and write it too. ParametrIQ CAD writes a 3D page as PRC and reads PRC models to show with a folded drawing.

Export

3D › Export › Export 3D Model…, choosing PRC, for 3D PDF (.prc), writes the 3D page as it is shown: folded as far as it is now, with its model.

• A part for each panel. Each panel, fold and bending part is a part of its own (a product occurrence, in PRC's terms), named as the 3D page names it, and placed where it is shown. Because each is placed on its own, a 3D PDF can move them: open and close the flaps, or fold the box.
• Its faces. Each part holds its outside, inside and cut edges, each a tessellated mesh (triangles with their normals), in the appearance's colours, opacity and gloss.
• Its artwork. The artwork printed on the outside and inside is a texture over the board's colour (a PNG, scaled down to 2048 pixels across if it is bigger), mapped as the 3D page maps it.
• The model. A 3D model shown on the page is written too, a part for each of its materials, with its textures.
• Units. The file is in millimetres, Z up, whatever the drawing's units.

Foil, varnish, emboss, the board's structure and its surface patterns, which the 3D page draws with its own shading, aren't written; nor are the floor and its shadows.

In a 3D PDF

File › Export › Export 3D PDF… writes the 3D page as a PDF page with the 3D model on it. Its 3D format is PRC to start with (or U3D, the older format). With PRC:

• the model is the one 3D › Export › Export 3D Model… writes as PRC, a part for each panel, the artwork as textures (or, with Artwork as textures off, the board's colours only);
• the fold (with Fold animation on) is played by the PDF's 3D JavaScript, as PRC has no animation of its own: when the page is shown it moves each panel from flat to as far as the 3D page is folded, over the seconds asked for, once or again and again (Loop). Folds and bending parts move with their panels but keep the shape they have on the 3D page, so they look right at its end. The script also has an unfold: a button of your own in the PDF can play either with getAnnots3D(0)[0].context3D.piqPlay("Fold") (or "Unfold"); piqStop() stops it;
• the PDF says it needs Adobe's extension level 3 of PDF 1.7, as PRC does. Adobe Acrobat and Reader show it; most other PDF viewers show the poster picture.

Import

3D › Models and Products › Import Model… reads a .prc file and shows it with the folded drawing, as it does a glTF, OBJ or STL model (see 3D pages). What is read:

• the file's tessellated geometry (triangles, triangle fans and strips), with the normals and texture coordinates it has (normals are worked out where it has none);
• each part placed by its product occurrences, their sub-assemblies and prototypes, and its own coordinate system;
• colours, materials and textures: a part's display style, its material's colour and opacity, and its texture (a PNG or JPEG, or pixels stored in the file);
• the file's unit: the model comes in in millimetres.

Left out, and said in the message after the import:

• parts that are exact geometry only (B-rep surfaces with no tessellation): save the PRC from its program with its tessellation (Acrobat and most CAD programs can);
• compressed tessellations, which some programs write to make files smaller;
• what can't be shown with a folded drawing: wires, points, markups (dimensions and notes), views and lights;
• anything in an assembly the file's tree doesn't let ParametrIQ read: its tessellations are then shown where they are, unplaced.

A PDF holding a PRC model isn't read as a model: export the PRC from it with Acrobat, or from the program that made it.

About the format

ParametrIQ writes PRC as Adobe's PRC specification and ISO 14739-1 describe it, version 8137 (Adobe Reader 9 and later): a header saying where each section is, one file structure (its globals, tree, tessellation and geometry, each compressed with zlib, and its textures' pictures uncompressed), and the model file naming the root of the assembly. Numbers are written in PRC's compact bit encoding, doubles in its compressed form.