Anatomy of an STL File

Quick Summary of main points on this post:

• STL files desicribe a mesh of triangles with no other information.
• STL files to not contain unit information
• STL files do not contain colour information*
• Some applications always export STL files in feet or inches
• 2 types of STL file - Always choose Binary as it makes smaller files.

STL is sometimes called Stereolithography Format or more properly Standard Tessellation Language. It has become the default file format for many single colour 3D printing applications. It was developed by Chuck Hull soon after he built the first 3D printer and the first specification was released in 1988.

Below is an example of the contents of an ASCII STL file that partially describes a cube drawn with one corner at the origin and with sides of length 1 unit. It is worth pointing out that there are two types of file STL format: binary and ASCII. They contain exactly the same information but the ASCII files will be much larger as they contain human readable text while the binary file is essentially a compressed version.

It can be seen that the contents of the STL file is very simple, it is essentially a list of coordinates that describe triangles and the normal that describes which direction each triangle faces. STL files describe a mesh of triangles with no other information. When exporting STL files, vector and nurbs based software may ask for a tolerance which is used to calculate how many triangles are needed to describe curved surfaces. Generally, the lower the tolerance the closer the triangles match the curve of the geometry and the more are required to create the form and so the large the file becomes.

One important thing to understand about an STL file is that it does not contain any information on what units are being used. The units used in any particular file will be determined by the software that was used to export the STL file. Usually the units will reflect the units that were used to model the geometry so if the model was modelled in meters the units will be meters, if the model was modelled in mm the units will be mm. However some software and export plugins that were written in the US may default all exported STL files to inches or possibly even feet.

solid
  facet normal -1.000000e+000 -0.000000e+000 -0.000000e+000
    outer loop
      vertex 0.000000e+000 0.000000e+000 1.000000e+000
      vertex 0.000000e+000 1.000000e+000 1.000000e+000
      vertex 0.000000e+000 1.000000e+000 0.000000e+000
    endloop
  endfacet
  facet normal -1.000000e+000 0.000000e+000 0.000000e+000
    outer loop
      vertex 0.000000e+000 1.000000e+000 0.000000e+000
      vertex 0.000000e+000 0.000000e+000 0.000000e+000
      vertex 0.000000e+000 0.000000e+000 1.000000e+000
    endloop
  endfacet
  facet normal 0.000000e+000 1.000000e+000 0.000000e+000
    outer loop
      vertex 0.000000e+000 1.000000e+000 1.000000e+000
      vertex 1.000000e+000 1.000000e+000 1.000000e+000
      vertex 1.000000e+000 1.000000e+000 0.000000e+000
    endloop
  endfacet

.....................................

  facet normal 0.000000e+000 0.000000e+000 -1.000000e+000
    outer loop
      vertex 0.000000e+000 0.000000e+000 0.000000e+000
      vertex 0.000000e+000 1.000000e+000 0.000000e+000
      vertex 1.000000e+000 1.000000e+000 0.000000e+000
    endloop
  endfacet
endsolid


In the future the STL file format is likely to be around for some years to come but in time it is likely that the format will be replaced by something like the AMF (Additive Manufacturing Format). Intitially known as STL 2, AMF is being designed on the XML (Extensible Markup Language) platform which means that it is flexible and can contain both geometry and additional information such as multiple materials and colours etc.

Since writing this in August 2013 a consortium of industry leaders has been formed to develop a new format known as 3MF. AMF has been pretty much dropped even though it became a viable format. As of March 2016 we have still not received an AMF file or had any enquiry about this format. 

These new formats are attempting to address the needs of 3D printing, additive manufacturing, copyright issues and other rights to reproduce. It is going to be complex and less accessible - I for one appreciate the simplicity of the STL file. "Simple is efficient" as my engineering drawing teacher used to say.

*In fact binary STL can support colour, if we save an STL from Magics we can open it again in Magics preserving the colour information. However the important point is that all of the STL file exporters written for 3D modelling software like Rhino, Revit, MicroStation, SketchUp etc do not export colour.


For further information about Lee 3D visit www.lee3d.co.uk

The Magic Of Magics RP

At the heart of Lee 3D is a piece of software called Magics.  This software is used around the world by leading RP and 3D Print bureaus to perform a number of critical functions that enable 3D parts to be fixed, optimised and built in most of the 3D printing machines available today.

Fixing and Optimising
Dealing as we do primarily with AEC data we use Magics for fixing and optimisation of files.  Fixing makes a file printable and includes simple tasks like filling holes, giving thickness to surfaces, stitching surfaces together and getting all of the faces (normals) in the file to face the right way.  Optimising makes a model look great and often reduces costs and includes thickening details, adding colour and textures, cutting up large models and hollowing. 

The real power of Magics is in it's optimisation tools.  These are tools that perform tasks that most CAD, BIM and other modelling applications are simply not built to do.  The  reason for this is that Magics has tools designed for certain functions but also because a meshed 3D print file is a much simpler dataset than a vector based CAD or a database driven BIM dataset. 

Key tools contained in Magics that vector based modelling applications either cannot do or struggle to do effectively are the cut, unify, hollow and the shrinkwrap tools. The shrinkwrap tool is an especially powerful tool but need careful use to ensure quality of output is maintained. It also can make use of a very powerful computer to fully exploit its strength.

A worked example - 1:50 figure

1. Textured SketchUp File opened in Magics and scaled - the little guy will be 36mm tall when printed (He came from Trimble 3D Warehouse and was modeled by Max Grueter)
2. Viewing of textures switched off to enable the errors to be clearly seen. Holes and bad edges are shown as yellow lines and inverted normals as red.
3. The errors are fixed leaving some of the parts too thin to print at 1:50. 
4. The file is optimised using the Shrinkwrap tool, adding 0.15mm all over and neatly retaining the image map on the new shell. The model is now robust and ready for 3D printing.

Viewing
The viewing tools in Magics are a joy to work with. Instantaneous section viewing, the ability to change rendering and logical colour, toggle visibility and mouse driven navigation all help to work with complex files with ease. 

Colour
The texturing tool allows aerial photographs etc to be draped onto the geometry and maneuvered to line the two up accurately. Textured data can be cut up and chopped about with no sign or marking in the 3D printed model.

For Architecture
The ability to open SketchUp and Rhino files natively, side steps many annoying export issues from these applications and greatly speeds up the process. In addition Magics opens a large number of files including STL, OBJ, VRML, PLY and 3DS.

It used to be that only bureaus and businesses with in-house machines used Magics but increasingly design offices that outsource 3D prints to a variety of suppliers, providing different technologies, are starting to bring Magics in-house.  It makes good business sense to have Magics in-house, if files can be checked before they go out you no longer have to rely on someone else to make decisions about the data when they are fixing it.  Once you have a printable file it speeds up getting quotes and in theory it allows you to get the job done at the best price.  Though of course there is a lot to be said for sticking with one same supplier (Lee 3D) who can provide uniformity of service.

And last but not least a Magics file has excellent compression algorithms which make much smaller files for sending and consequently saving time in the process.

_______________________________________________________________________

Lee 3D offers the following services in addition to 3D print bureau services:

File preparation services
File fixing and optimisation of files for 3D printing specialising in architectural, engineering and construction.  This service is offered globally.

Magics Training
Magics training is offered on-site or by Webex. Half day courses are available for beginners and advanced users who wish to use Magics for preparing architectural data for 3D Printing.

Magics Sales
The decision to buy Magics needs to be taken with the knowledge that you will get the right support.  Lee 3D offer user support for using the software in the AEC sector and in addition to this you also have access to support direct from Materialise. 

To find out more about Lee 3D visit www.lee3d.co.uk

Colour 3D printing of GIS Data

3D printing is underused as a design and communication tool in many sectors. In particular colour 3D printing could be much more widely used as a communication tool in the Energy, Environment, Marine and Coastal, Transport and Water engineering sectors. This is I believe is partly due to lack of knowledge of the techniques and difficulties in getting data out of many software applications for 3D printing. 

Designers using ArcGIS for example can export VRML files which contain colour information. So any of the information in the software model can be exported and 3D printed as a physical colour model. This should present opportunities for engineers working in all of the fields where ArcGIS is used and where communication to a wider audience is required. 

Any combination of map information and topographical
geometry can  be 3D printed.

There is perhaps a tendency for many professionals to stay within software, where constant change is the name of the game. 3D printing a physical model fixes the system at a given point. However if you have public consultation or planning requirements and lets face it none of these disciplines work in isolation from the public, a 3D printed topographical model overlain with graphical information can be a powerful tool. A physical model can convey complex layers of information in a way that is just not not possible with with paper or screen. Importantly a colour 3D print can communicate information to stake holders that are not experts in interpreting technical information.

Last time I received a file exported from ArcGIS the exporter was not working properly and required some manual editing to complete the work. Which leads me on to the second reason why 3D printing is underused in many sectors and that is that software vendors have not built coherent export features to enable 3D printing from their software. Too often it is a plugin or an extension that needs to be bought or downloaded. What is needed here is vision and leadership within software companies to get the most out of their software.

A great many of the mature design products like MicroStation and ArcGIS have VRML export capabilities, not to enable colour 3D printing, but because 15 - 20 years ago developers thought that VRML would enable them to create dynamic 3D models on the web. However this does mean that many kinds of 3D software are able to export colour 3D models that with a bit of work can be made in to physical 3D models.

Note:
Exporting VRML from ARCGIS requires ArcGIS for Desktop with 3D Analyst extension.


For more information about colour 3D printing visit www.lee3d.co.uk

3D printed model for Harrison Sutton Partnership

Totnes architects, Harrison Sutton Partnership commissioned a 3D printed model for the Vinery project in Devon. The two buildings that nestle in the steeply sloping site were to be removable. 

Re-using their design development SketchUp model, Lee 3D prepared and optimised the file for 3D printing using Magics RP. A scale of 1:200 was chosen balancing cost with clarity of features. Consideration was given to ensuring the removable buildings were a good fit with the site model. The model was 3D printed on the ZPrinter 650 as a monochrome model. 

The model is shown below in various states showing the buildings and base part. 

For more information about Harrison Sutton Partnership visit www.harrisonsutton.com

For More information about 3D Printing with Lee 3D visit www.lee3d.co.uk

In what way is 3D printing cost effective for architects?

Recently while making a CPD presentation to a medium sized architectural practice in London, I posted a slide listing the strengths of the 3D print technology we use at Lee 3D. The strengths named were speed, aesthetic quality, colour and cost effectiveness. One of the architects asked what I meant by "cost effective" and in this blog post I will try to answer that question more fully.

Of course the ZPrinter technology we use is comparatively less costly to run than many competitor technologies but this is not the whole story, it begs the question: 

Why 3D print a model in the first place?

To get to the bottom of this we first need to ask what 3D printing is useful for in architecture. 3D printers may one day be used to print buildings directly, as being researched at Loughborough University and D-Shape, but at the current time 3D printing is primarily used as a communication tool in the design process. Typically this involves 3D printing models for communication purposes.

3D printing allows a direct output from a 3D software model into physical form. So the first argument for cost effectiveness of 3D printing might be that 3D printing integrates with the computerised design process that most architects use today. 3D printing allows the reuse of design data and with the increased use of 3D design data with the inexorable move to BIM, new opportunities for reusing this data are constantly unfolding.

But still we need to explore the reason why bother to make the 3D print in the first place. What is the pay off?

As a communication tool a physical model has the ability to express geometry to an audience in a way that is simply not possible on paper or screen. When a model is placed on a table in a meeting the facts of the design geometry are immediately clear for all to see. 

We all know that architects are trained to read architectural drawings and images, however it is also a fact that not all clients and stakeholders are equally able to do this. A physical model democratises the communication of design geometry.

In certain practices and for certain projects, 3D printing is used extensively for internal review of design geometry. A physical model as part of a presentation saves time in understanding form.  If a form is complex it may be the only way to really understand it. 

Each media and technique has the ability to communicate different kinds of information. A good visualisation superimposed on a photograph of the site can give an impression of what a design will feel like in a way that a 3D print probably cannot. 3D printing is great at clearly expressing the actual physical geometry of the design, accurately, to scale and direct from the design workflow.

3D printing serves a purpose in communicating designs, especially at early stage when a traditionally made model may convey too much information and cost too much. 

And here's the crunch, with 3D printing most effective in the early stages of designing, it can be used to influence decisions. A 3D print can help win work. 3D prints at a very early stage communicate ideas to a client in a clear and powerful way.

Conclusion
So in what way is 3D printing cost effective for architects? 

     3D printing:

1. Allows reuse of 3D software models.
2. Clearly communicates design geometry to clients and other stakeholders.
3. Saves time in understanding form.
4. Helps win work.

To find out more about 3D printing for building design visit: www.lee3d.co.uk

3D Printing Architectural Context Models

The availability in the UK of 3D city models from ZMapping and other suppliers has enabled the production of accurate, detailed 3D printed context models. At Lee 3D, I made some samples to look at different colouring effects that can be achieved.

How you choose to present a context model will depend on house styles and the purpose of the model. Some customers prefer not to see all of the clutter on top of each building while for others the parapets, chimneys and dormas help to express the texture of the city. A context model for a residential model for marketing purposes may need to be softer in tone than one featuring a multi-storey office building.

Tile 01
This 1:1000 sample was printed white but with grey roads. It also shows the site area that has been recessed to 9mm to enable 2 or 3 floors of basement to be represented on the removable plug.

Tile 02

In contrast this sample has buildings printed in light grey, roads a darker grey and the to ground a light brown and green to represent a grassed area. The result is a much softer effect than Tile 01 where the contrast between grey and white is more strident.

Tile 03

The neutral uncoloured model can allow the proposed building to stand out. Trees are printed as symbolically and roads are recessed very slightly to give an indication of their presence with out crying out for attention.



Tile 04

In this sample an aerial photograph has been projected onto the topography. This technique is probably least effective in an urban model with high buildings as building tops can loom over pavements depending on the angle of the photograph. However in more rural models with less geometric interest the aerial image comes into its own.

  

Colour can be used to as a tool to communicate zoning and indeed some of the most effective 3D printed context models are waterfront models where the water is coloured blue and the land is left a neutral white. Attempting to apply real colours and textures at a scale of 1:500 or smaller can lead to a muddy effect. It is usually better to work with a limited palette of flat colours.

Size is very much going to be determined by the purpose of the model being made. A context model where sensitive areas of historical interest are concerned may require a larger tiled model to convince a planning team of the merits of a proposal, whereas a speculative model designed to win the interest of a prospective client may just need surrounding streets to give the proposal some sense of proportion. (At Lee 3D our maximum tile size is 380 x 250mm.)

Scale is often determined by the function of the model. Data in this format can be successfully printed down to scales of 1:5000. A model at this tiny scale may need to be made to give assurances that sightlines to a distant landmark will not be affected. If the purpose of the model is to create a removable plug that represents the site/proposed design then the detail required will have an effect on the chosen scale. Scales of 1:1000 and 1:500 are typical for this kind of model.

Image showing Tile 01 with model makers trees and insert building added. 

Dressing models with model makers trees adds a final level of environmental detail. Larger trees do not 3D print well at 1:500 and larger scales. Adding model makers trees does add quite a bit of time to the process of 3D printing a context model but if time allows it is probably worth it.

Insert models could well do with an entire blog article of their own so I will not attempt to cover this here.

Aldwych 3D printed from ZMapping data at Lee 3D

For more information about ZMapping data visit www.zmapping.co.uk

For more information about 3D printing at Lee 3D visit www.lee3d.co.uk



Architects - beware of consumer 3D printers!

Recent discussions at Lee 3D with architects investigating 3D Printing of architectural models have shown a disturbing trend towards architects buying consumer 3D printers that just don't work for them.

Three practices of different sizes illustrate the experiences encountered with these machines: 

Firstly, a one man band approached Lee 3D annoyed that his machine was not working and that when it did it was unable to produce the geometry he wanted to print - his machine was a single material machine that meant there was no support material and therefor the machine is entirely limited to certain geometries. He asked if the ZPrinter/CJP machine we use can print lolly pop style trees at 1:1000 scale - which of course it can - and in colour too.

Secondly, a small rural practice had their duel extruder machine back in the box it was delivered in. The complaint here was that the machine was much too slow to print anything of any substance and again the geometry was a problem. This machine can print support material so in theory it can print overhangs etc. However the support material needs to be broken away from the model which meant their delicate models were damaged in the process. In this case the ZPrinter parts we made for them impressed in both level of detail and speed of delivery.

Thirdly, a large 100 strong practice where the model maker has built a 3D printer from a kit. This involved a large investment in time and effort and ultimately only lead to very limited parts that needed significant finishing to include in models.

Despite these three seemingly entirely negative experiences I can report that owning a machine did enable all of these users to work out how to create suitable 3D software models that would, if their machines were capable, 3D print successfully.

I would suggest that the £1,000 - £2000 and time invested would be much better invested in working with a good bureau (Lee 3D) to understand the software requirements and then to produce a great set of models of sufficient quality that could actually be used on live projects or to win new business.

One advantage of going to a bureau is that there will be (should be) a huge amount of experience available to avoid mistakes and to guide customers towards a high quality product. Another advantage of using a professional level bureau is that they will have professional level kit that takes away the risk involved in buying kit for in-house use. 

To illustrate the point the image below shows a bracelet printed on a consumer 3D printer. Its actually pretty good in that it is flexible and reasonably robust and the geometry is interesting. But you need to realise it the printer is limited to this kind of geometry - whereas the colour 3D print in the background is pretty much geometry independent and is is printed in one take with full colour (model makers trees and acrylic cover added afterwards).

Visit the Lee 3D website for more information about colour 3D printing.