---
title: "PDES, ACIS and Parasolid short notes"
subject: "Computer Aided Design"
chapter: 6
key: "semester_4/computer_aided_design:pdes-acis-parasolid-notes"
source: https://www.bctengineer.com/q/semester_4/computer_aided_design/pdes-acis-parasolid-notes
site: BCT Engineering
---

# PDES, ACIS and Parasolid short notes

Computer Aided Design · Chapter 6: CAM and Recent Technology

- Asked in: year not given, 4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/computer_aided_design/pdes-acis-parasolid-notes
- Whole chapter: https://www.bctengineer.com/md/semester_4/computer_aided_design/chapter-6

## Question

Write short notes on PDES, ACIS and Parasolid.

## Short answer

PDES (Product Data Exchange using STEP) is a neutral standard for exchanging complete product data including shape, tolerances, and materials, which merged into ISO 10303 (STEP). ACIS and Parasolid are 3D geometric modeling kernels; ACIS (from Spatial) supports solid modeling with SAT files, while Parasolid (from Siemens) uses .x_t and .x_b files for precise solid exchange between CAD/CAM systems.

## Answer

#### PDES
**Product Data Exchange using STEP** was a US initiative of the late 1980s (NIST and industry) to define a neutral way of exchanging complete product data, not only geometry. It was developed together with the ISO group working on STEP, and merged into **ISO 10303 (STEP)**. It covers shape, tolerances, materials, assembly structure and life-cycle data, and was meant to replace IGES.

#### ACIS
ACIS (by Spatial Corporation; the name is commonly explained as "Alan, Charles, Ian's System", after its original developers) is a **3D geometric modelling kernel** written in C++ and licensed to many software vendors. It handles wireframe, surface and solid (B-rep) modelling, Boolean operations, blending and offsetting. Its native file is **SAT** (ASCII) or **SAB** (binary), which is used to transfer solids between ACIS-based systems (for example SpaceClaim, BricsCAD, and early versions of AutoCAD and Autodesk Inventor).

#### Parasolid
Parasolid is a B-rep **solid modelling kernel** (originally from Shape Data, now Siemens). It supports solids, sheets, wires and free-form NURBS surfaces with robust Booleans. It is used in NX, SolidWorks, Solid Edge and many CAE/CAM tools. Its transmit file formats are **.x_t** (text) and **.x_b** (binary), which allow direct transfer of exact solid geometry between Parasolid-based software without loss.

| Item | Type | Native files |
|---|---|---|
| PDES | Data-exchange standard (became STEP) | STEP (.stp) |
| ACIS | Modelling kernel | .sat, .sab |
| Parasolid | Modelling kernel | .x_t, .x_b |

Kernel-based formats keep exact (not faceted) geometry, so they are better than STL for CAD-to-CAD exchange.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What was PDES?
   A. A modelling kernel
   B. A US product data exchange initiative that merged into ISO 10303 (STEP)
   C. A 3D printing format
   D. A CNC language
   Answer: B. PDES aimed at complete product data exchange and became part of STEP. (Key point: PDES)

2. What is ACIS?
   A. A 3D geometric modelling kernel in C++ whose native files are SAT/SAB
   B. A neutral standard replacing STEP
   C. A 2D drawing format
   D. A rapid prototyping machine
   Answer: A. ACIS is licensed to vendors and uses .sat (ASCII) and .sab (binary) files. (Key point: ACIS)

3. Which describes Parasolid correctly?
   A. A B-rep solid modelling kernel using .x_t and .x_b transmit files, giving exact geometry transfer between Parasolid-based software
   B. A faceted mesh format
   C. A US exchange initiative
   D. A machining language
   Answer: A. Parasolid (now Siemens) is used in NX, SolidWorks and Solid Edge; it keeps exact geometry, unlike STL. (Key point: Parasolid)