[x3d-public] [cad] STL File Format for 3D Printing - Simply Explained | All3DP

Mon Aug 14 08:21:49 PDT 2017

Hi, Roy and Michalis -

In addition to the quote from the spec, an Inline node must also handle
IMPORT and EXPORT mappings. At SIGGraph and at the WG6 meeting, we discussed
specifying ExternalGeometry and/or ExternalShape nodes. While they are
intended for importing glTF content, there is no reason why they couldn't
also handle STL if am implementered desired it. The purpose of these two
nodes is to allow content ready for rendering to be bulk loaded into a
geometry processor (or geometry processor simulator J) with little or no
interpretation, thus greatly speeding the handle of large amounts of
geometry. The difference between ExternalGeometry and ExternalShape is that
ExternalShape can also include appearance information as specified in glTF.

n  Dick

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From: cad [mailto:cad-bounces at web3d.org] On Behalf Of Roy Walmsley
Sent: Monday, August 14, 2017 3:21 AM
To: 'Michalis Kamburelis'; 'Don Brutzman'
Cc: 'X3D Design Printing Scanning working group'; 'X3D Graphics public
mailing list'
Subject: Re: [cad] [x3d-public] STL File Format for 3D Printing - Simply
Explained | All3DP

Hi,

Thanks for following up with this Michaelis. I was particularly interested
to note that you permit an Inline node to read an STL file (as well as
others, perhaps). I assume you simply specify the STL file in the URL, and
your code selects an appropriate reader depending on the file extension
and/or reading the header.

I looked at the standard to see what it might have to say on this topic, in
ISO/IEC 19775-1:2013, clause 9.3.2 X3DUrlObject

Reference:
http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components
/networking.html#X3DUrlObject

The third paragraph is particularly relevant. It reads:

"Each specified URL shall refer to a valid X3D file that contains a list of
children nodes, prototypes and routes at the top level as described in
10.2.1 Grouping and children node types. The results are undefined if the
URL refers to a file that is not an X3D file, or if the X3D file contains an
invalid scene." 

To permit loading of file types other than formal X3D files this text would
have to be modified.

All the best,

Roy

-----Original Message-----

From: x3d-public [mailto:x3d-public-bounces at web3d.org] On Behalf Of Michalis
Kamburelis

Sent: 14 August 2017 04:35

To: Don Brutzman <brutzman at nps.edu>

Cc: X3D Design Printing Scanning working group <cad at web3d.org>; X3D Graphics
public mailing list <x3d-public at web3d.org>

Subject: Re: [x3d-public] STL File Format for 3D Printing - Simply Explained
| All3DP

2017-08-14 3:35 GMT+02:00 Don Brutzman <brutzman at nps.edu>:

> Good article of general interest:

> 

>         STL File Format for 3D Printing - Simply Explained | All3DP

>         June 13, 2017 bub Dibya Chakravorty

>         

> https://all3dp.com/what-is-stl-file-format-extension-3d-printing

> 

> Interesting thought question:

> 

> -if we follow Fraunhofer's SRC pattern and have both ExternalShape and 

> ExternalGeometry nodes,

> -  and now replace SRC with glTF 2, then

> - might we similarly allow loading of STL models in ExternalShape and 

> ExternalGeometry nodes?

> 

1. view3dscene https://castle-engine.sourceforge.io/view3dscene.php

can already read STL files (both text and binary encodings) and render them,
and convert to X3D. You can also use "Inline" node to include STL files
inside a larger X3D scene.

2. STL became a standard format for 3D printing, but it's simplicity comes
at a price. It does not carry *any* information beyond coordinates and
normals.

  This is not a criticism per se -- the STL simplicity works great in some
usecases, like 3D printing.

  But for visualization, when you want to show something "pretty" (not only
to check whether your shape is correct), you will usually want something
more. At least simple 2D texture coordinates. And STL does not allow them.
(Not to mention colors per vertex, multiple texture coordinates, custom
shader attributes...).

Regards,

Michalis

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