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Posted 5 Mar 2003

StL Data File Viewer

, 5 Mar 2003
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A simple StereoLithography data file viewer.

Sample Image - StLViewer.jpg


StereoLithography(StL) is something that is widely used in CAD/CAM, RapidPrototyping etc. The concept is that any surface or solid is exported to StL format by data exchange packages after they are modeled in commercial CAD packages. This data consists of triangulated facets that approximate the surface of the solid. No topological or geometric information is exported. The surface is subdivided into small triangles. The approximation uses chordal deflection for curved surfaces to smoothen the surface. More the smoothening required, more number of smaller triangles are generated by subdivision resulting in larger size of data file. Now, along with triangles, their facet normals are also generated. The data is written both in ASCII and binary formats. The data in ASCII is written like this:

facet normal  0.000000e+000 -1.000000e+000  0.000000e+000
   outer loop
     vertex -1.499999e+002 -1.000000e+002  0.000000e+000
     vertex -1.500000e+002 -1.000000e+002  0.000000e+000
     vertex -1.500000e+002 -1.000000e+002 -5.000000e+001

The facet normal tells the three components of the facet normal followed by three vertices of one triangle, enclosed by the statements.

facet normal  0.000000e+000 -1.000000e+000  0.000000e+000



Thus all the triangles are written one after the other. This data can be then used as input for generating Rapid Prototype models as well as for NC toolpath generation. The Normal data helps to compute tool offsets etc.

Here, for displaying the data in the OpenGL viewer, I have written the code for reading the data and displaying each triangle using glBegin(GL_TRIANGLES) and the normals for lighting. The viewer and geometry coding is same as my earlier project CadSurf. You can read as many StL (ASCII only) files into the viewer zoom, pan, rotate the views, select the objects, change attributes like color and material. The viewer provides object oriented context menus. I.e., when you click the right mouse button in the view with no active selection, you get a context menu for setting the viewer attributes, whereas with StL object selected, you get menu for the object attributes. Some sample StL data is also provided in the Data folder of the project.

Please let me know your comments. Thank you.


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Product Manager Mahindra & Mahindra
India India
Sharjith is a Mechanical Engineer with strong passion for Automobiles, Aircrafts and Software development.

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Comments and Discussions

GeneralSlow and Selection should disabled out of the stl object Pin
lua8-Jun-05 2:03
memberlua8-Jun-05 2:03 
GeneralRe: Slow and Selection should disabled out of the stl object Pin
hero3blade24-Sep-05 17:09
memberhero3blade24-Sep-05 17:09 
GeneralCould not complie a code Pin
Tejas_qp1-Mar-05 9:00
memberTejas_qp1-Mar-05 9:00 
GeneralRe: Could not complie a code Pin
Sharjith3-Mar-05 22:22
memberSharjith3-Mar-05 22:22 
GeneralRe: Could not complie a code Pin
1vs18-Apr-05 20:44
member1vs18-Apr-05 20:44 
QuestionHow to run 2 different(or same) OpenGL objects in one DialogBox? Pin
werter15-Jun-04 22:53
memberwerter15-Jun-04 22:53 
GeneralOT: Starting Point Pin
lj993234-Aug-03 17:48
susslj993234-Aug-03 17:48 
GeneralRe: OT: Starting Point Pin
jcdemo17-Mar-05 21:50
memberjcdemo17-Mar-05 21:50 
Whoever wrote this code certainely had a very good look at OpenCascade. I suspect many of the concepts in this viewer (as well as in the CadSurf app) come directly from Cascade, but simplified (thanks for that!). Unfortunately, the app suffers from similar performance issues as the original OpenCascade library - possibly because it uses a similar approach of separating geometry from graphic objects as well as using the concept of display context on top of OpenGL context. If you can live with performance limitations this is a really nice way to create an application with very high end features similar to what you can find in OpenCascade, at a much lower investment of time and money (using OpenCascade is not as "free" as one would think). Thanks to the author for this contribution.

GeneralCan't not #include <GL/glut.h> Pin
ICE_WIZARD24-Jul-03 8:25
memberICE_WIZARD24-Jul-03 8:25 
GeneralRe: Can't not #include <GL/glut.h> Pin
Jonathan de Halleux24-Jul-03 8:35
memberJonathan de Halleux24-Jul-03 8:35 
GeneralSTL viewer does not display Pin
reddnedk23-Jun-03 7:18
memberreddnedk23-Jun-03 7:18 
GeneralRe: STL viewer does not display Pin
Sharjith26-Jun-03 6:14
memberSharjith26-Jun-03 6:14 
GeneralRe: STL viewer does not display Pin
Anonymous2-Jul-03 20:09
sussAnonymous2-Jul-03 20:09 
Generalview Pin
mcalves@coc.ufrj.br8-May-03 21:05
membermcalves@coc.ufrj.br8-May-03 21:05 
QuestionHow does GL_SELECT mode work in MFC? Pin
killerdoll18-Mar-03 6:33
memberkillerdoll18-Mar-03 6:33 
AnswerRe: How does GL_SELECT mode work in MFC? Pin
Sharjith28-Mar-03 3:01
memberSharjith28-Mar-03 3:01 
General0xC0000005: Access Violation. Pin
Sorry I donnot know why I cannot fill in right con7-Mar-03 14:33
sussSorry I donnot know why I cannot fill in right con7-Mar-03 14:33 
GeneralRe: 0xC0000005: Access Violation. Pin
Sharjith7-Mar-03 20:48
memberSharjith7-Mar-03 20:48 
GeneralRe: 0xC0000005: Access Violation. Pin
My name is Iain Scott. Does it matter that there a25-Jun-06 2:12
memberMy name is Iain Scott. Does it matter that there a25-Jun-06 2:12 
NewsRe: 0xC0000005: Access Violation. Pin
Sharjith28-Jun-06 23:00
memberSharjith28-Jun-06 23:00 

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