Smart Replicas

Looking for easy methods for archaeological ceramic objects reproduction.

Artec Spider 3D scanner

While still being occupied with the processing of the CT-scans, the first impression was that it wasn’t as easy and accurate as we expected it to be. Maaike had reserved the Artec Spider for Friday for another project. We wanted to see if this scanning technique gave a better or different result then the CT-scanners. We were lucky that this was possible.

The Artec Spider is a scanner for small objects that captures really complex details and color. It has an accuracy up to 0.05 mm.

We scanned three objects:

  1. The comb, because this object is the only object that was scanned by the macro and micro scanner. Scanning this object with the Artec Spider will show the difference between these three scanners.
    DSC_0326
  2. Hermione, to see if the accuracy of details is better with the Artec Spider.
    DSC_0329
  3. Harry, to see if with this technique the break lines and repaired break lines will be visible
    In the files from the CT-scanner the repaired break lines weren’t visible and the break lines were given an arched shape.

The objects and the scanner had to be moved/operated by hand, since the objects were so small. For the comb this wasn’t a problem because we put it in a paper cup and turned that around. The scanner has problems with really small or big gaps. The small gaps in the comb were too small, in the model there was a relief instead of gaps.
The problem with Hermione was the big gap on one side. Because of the gap the model had a lot of failures. We tried multiple ways of scanning. Eventually we scanned only the handle, by making multiple scans from different angles and combining them together.
Because of the problems we had with Hermione we decided to fill Harry with a napkin, so that no problems would arise from the difference in distance. This went ok, only afterwards the napkin had to be deleted.
The results of processed 3D images will be posted later.

Meeting recap (6th of October)

To keep you up to date we would like to introduce of pending and active processes of the project.

Currently we are focusing on two main subjects: production techniques (Jorinde and Irene) and image processing (Sander and Kotryna). For the first one we plan to publish a page later today which will be updated as we gather information. For the second, we have already posted an overview, but since we are still waiting for the trial versions of some of the programs a second article will follow.

As expected, we are lagging with the step “CT-scans to .stl”. The reason for that is the low quality of already produced .stl files and inability to open the .dcm files.

Our plan A is to finish with it today or tomorrow depending on the outcomes from the trial versions of the program. Then on Thursday make the individual models of object “Harry” with production technique ideas. We will pitch them to each other on Friday morning, hopefully resulting in 2-3 final ideas which will be sent for production in the same afternoon. Most important notes for the preparation of these pitch files are:

  1. Thinking about the ability to produce
  2. Retaining the historical footprint
  3. Trying to make smart joints between different materials, since the current holes have very rounded corners (also a part of 1.)

Plan B would come into action if we cannot get the .dcm files to work or the quality of the scans is very low. This would lead to post-processing of already prepared 3D files of object “Dobby” to make the surfaces smoother and the break lines sharper. That would mean that we would loose a lot of data: including the micro-scans, which would be used for the comparison of all the scanners that we used. Yet we would still follow up the plan A from Thursday by shifting it 4-5 hours.

In conclusion, even though we are slightly behind primary schedule, we have received valuable insights in what programs to use and what to expect of them. Moreover, even if we loose the .dcm files, we would still be able to produce what we strove for in the beginning: just the final model would be less spectacular.

Keep your fingers crossed for us and till Thursday!

Comparison of image processing software 1

Directly after receiving the scans on Tuesday we jumped into processing them into 3D models. To keep it clear we used “Hagrid”(obj. 5) as an example for all of the programs.

As noted in the previous post, this process has multiple steps and in order to gain the highest level of detail, a lot of tweaking is necessary.

The usual procedure goes as follows:

(0. Changing the .ima or .dcm files into program compatible format. Most of our scans were made in .dcm format which was not compatible with multiple programs: so far we tried RenameMaster, which did not work)

  1. Loading the .dcm or .ima files into a 3D processing program. These file formats actually contain only 2D information: the sections of the object. In other words, the 3D model is an interpretation of multiple sections and therefore steps between them might be visible, if the resolution is not high enough.
  2. Selecting threshold and filtering the right information. Depending on the program this step might be automatized. If not, it might be very heavy on your computer. Therefore, a device with a good graphics card and 16GB RAM is advised (it would work on 6 or 8GB RAM, but it goes slow and tends to crash often).
  3. Loading the 3D file into a volume renderer to get an editable mesh (.stl). 

To begin with, we started with Seg3D. This program did not want to read .dcm files, thus we only worked with test files, which were in .ima format. The interface was clear, but to extract minuscule details it needed a lot of filtering and playing with histograms. That was extremely hard on our computers (6-8GB RAM, 2.0-2.03GHz) and took over an hour to get a decent file. Moreover, the final result is given in .nrrd format which later has to be translated to .stl with the help of ImageVis3D. The file looked rather detailed in Seg3D, but the final .stl was worthless.Capture

Hagrid_Seg3D to ImageVis3D_128x128x54mesh_detail

Later on, we received a tutorial from an past student of our supervisor Maaike. It suggested using DeVide. Unlike the previous program this one works on the basis of visual programming. Thus all of the steps can be easily retraced. This program can directly export to .stl reducing the possibility of getting a very rigid mesh, like with Seg3D. Unfortunately, the program did not want to work on our computers.

After this failure we contacted one of the researchers in the faculty of Industrial Design Engineering. He adviced to try out the following programs:

  1. 3D slicer (open source)
  2. Avizo (paid, evaluation copy available after contacting the firm)
  3. Mimics (paid, evaluation copy available after contacting the firm)

The first of the list (3Dslicer) proved to be very user friendly (although it did not read the .dcm files). The information is collected automatically after choosing a preset and is quite precise. One can also select if to smooth the surface: both outputs are interesting in form, with the edgy one as an expressive interpretation of a kitschy object of the past. If used for the final product, more mesh post-processing is necessary

3DSlicer_screenshot

Hagrid_3DSlicer_nonsmoothedges_detail (1)

Hagrid_3DSlicer_smoothedges_detail

To be continued…

Making choices

We had to make some choices since there were  a lot of bowls, plates, hair brushes and other ceramics. To distinguish them we gave them names. We joked about ‘Harry Pottery’ and decided to choose the names from Harry Potter characters. We based our choices at differences of advantages and interesting characteristics. Since we didn’t know how much time it would take to digitalise the cups and plates, we numbered them in order of importance.
We took in account the different types of advantages.

  1. Holes
    To make the cups useful again, we need to fix the holes.
  2. Details
    Some cups like Harmione and Hagrid have some nice details. Since the CT scanner is not that accurate we have to find other solutions for bringing those details back.
  3. Fixing techniques
    There are different ways used for fixing the objects. How can we translate those methods in our new design?

all

We decided to exclude the hair brushes in our process, because it has nothing to do with tableware.

1. Harry
Bowl with interesting holes the missing shards left. Diameter of +/- 15 centimeters.
2DSC_0344a

2. Hermione
This one has some nice decorations. Diameter of +/- 12 centimeters.
3 DSC_0331

3. Ron
Here the advantage is to replace the three separate shards. Diameter of +/- 18 centimeters.
2ron2
4. Ginny
Small plate. Missing a piece and two repaired cracks. Diameter of +/- 15 centimeters.
2DSC_0361


5. Hagrid
Kind of fruit bowl with lid. It has nails and glue as fixing methods. The cracks are really fragile, but as good as complete. Diameter of +/- 25 centimeters.
5DSC_0294

6. Dobby
We liked this small cup because of its small hole. Diameter of 5 centimeters.
2DSC_0315

7. Snape
This one is familiar to Hagrid, but much smaller. The one defect is the bottom which is fixed. The cup is complete. Diameter +/- 15 centimeters.
1 DSC_0305

CT-scanning and priorities

As the project slowly went into motion we had the first digitizing session in the laboratory of Geosciences&Engineering. Our group was provided with the luxury to first hand observe both micro- and macro-CT scanners in working. Both with their advantages and limitations, they gave us a new perspective of how to order and process given archaeological objects.

When Maaike came in with boxes full of ceramics from the Archaeological archive of Amsterdam, we understood that it was neither efficient, nor possible to scan them all. At this point selection was crucial. At first sight we had three main groups of objects: lice combs (highest level of detail), broken colored ceramics bound with metal strings (necessity to make more detailed scans to understand the technique) and sets of white ceramic tableware lacking multiple shards.

DSC_0381DSC_0307Detail hermione

The latter seemed to be the closest to the issues visible in the goal of the project. Yet the other two gave us interesting side paths which would improve overall understanding of the methods and possibilities of 3D scanning. Based on this, we made a queue sorted by importance, which would lead to at least one object of a group scanned.

DSC_0292

After the first inspection of the digitized forms we were rather amazed that the precision of 0,3mm was not sufficient for some of the fine-detailed specimens. E.g. the combs lost their teeth, metal bindings were muffled, crack lines barely visible. Consequently we were offered to work with much finer machinery (micro-CT scanner) mostly used for small scale material research. Yet the time and money needed for this method led to only two specimens scanned: the finest ivory comb and a detail of a metal connection. In total we got 13 scans, excluding identical scans in higher precision. The notes and conclusions after this are as follow:

1. There are 2 CT-scanners in the Geoscience&Engineering laboratory:

  • Macro-scanner can be used to scan rather big objects, but the fine details are almost completely neglected; object is stationary, thus there is a small chance of damage. Precision 0,3mm.
  • Micro-scanner is very slow (1h per object) and has very limited object size: till 100-120mm in diameter; object is rotating, thus it needs to either be glued or fixed, which requires extra attention not to damage the object. Precision 0,03mm.
  • Both scan only the form and not color; they can detect cavities, but not slight changes in the material density

2. The digitized forms are saved as 2D images of section cuts in .dcm or .ima file format, which need multiple steps to be converted into editable 3D objects. Even though we were informed that it is a very quick procedure, to gain fine details it is necessary to have a powerful computer(16GB RAM) and correct software (which is usually paid).

Introduction

Welcome to the logbook of the research project Augmenting Prototypes: Smart Replicas. This project is a part of half year bachelor program “Advanced prototyping” in TU Delft.

Smart Replicas is the result of a collaboration between Archaeological department Amsterdam and design studio Maaike Roozenburg. The latter supervises 4 students preparing material for this blog.

The focus of the project is the usage of CT scans to recreate and analyse repaired and/or unusable archaeological findings of everyday use.The aim of this is to replicate and improve given objects, while not losing the historical footprint. In other words, the blog will revolve on modern techniques of digital and physical reproduction.

The simplified planning will follow the scheme provided below. Each set of steps will be described in a weekly report, which will complimented with an occasional review of the field.

Project Approach

© 2011 TU Delft