Chapter 2: Data Collection
Now that you have a basic idea about how 3D scanning and modeling works, let’s really get started. Before you can have a 3D model, you must have 3D data to create that model. Let’s start there…
So, what are the ways that 3D data can be collected?
There are multiple ways to collect 3D data but two of the most common methods (and the two most frequently used by Direct Dimensions) are laser scanning and digitizing.
During laser scanning, a laser line is passed over the surface of an object in order to record three-dimensional information. The surface data is captured by a camera sensor mounted in the laser scanner which records accurate dense 3D points in space, allowing for very accurate data without ever touching the object.
Laser scanners can be broken down further into types such as laser line, patch, and spherical. The FARO ScanArm, the FARO LS, the Surphaser, Konica Minolta Vivid 9i and Range 7 are some examples of laser scanners that we often use at Direct Dimensions.
The second major method is digitizing, which is a contact based form of 3D data collection. This is generally done by touching a probe to various points on the surface of the object to record 3D information. Using a point or ball probe allows the user to collect individual 3D data points of an object in space rather than large swathes of points at a time, like laser scanning. This method of data collection is generally more accurate for defining the geometric form of an object rather than organic freeform shapes. Digitizing is especially useful for industrial reverse engineering applications when precision is the most important factor. Stationary CMM’s (coordinate measurement machine), portable CMM arms, and the FARO Laser Tracker are all examples of digitizers that we often use at Direct Dimensions.
Other methods of collecting 3D data include white light scanning, CT scanning and photo image based systems. These technologies are being utilized more frequently in the field of 3D scanning and new applications are being discovered every day.
To be digitized or laser scanned?
A general “rule” is that scanning is better for organic shapes and digitizing is most accurate for geometric shapes. In general, laser scanning is also used for higher-volume work (larger objects like cars, planes, and buildings). Laser scanning is also a great option for people who need 3D data of an object but would prefer that the object not be touched, such as for documentation of important artifacts.
Digitizing is often used for our engineering projects and first article inspections, in instances where precise measurements are required for geometrically-shaped subjects. This includes objects that have defined lines and planes and curved shapes, like spheres and cylinders.
This doesn’t mean that you can never laser scan a part with many geometric features or that you can’t digitize a plane (an entire plane can be digitized, believe us - we’ve done it!) or even a sculpture. These are just rules of thumb.
Utilizing multiple methods of Data Collection
There are projects when it is more cost and time effective to use multiple methods of data collection. A good example is a cast part with geometric machined features. You might need a 3D model of the entire part but really need incredible accuracy on the machined features while the freeform cast surface itself is not as important. In such a case it can be much more effective to laser scan the entire part and then digitize the geometric features. The data can be combined during the modeling phase (more on that in the following chapters).
Additional Scanning Information
Because you are trying to collect the most accurate data possible, there are a few more things to keep in mind before you run out and start scanning everything in sight.
* Bright light sources in the area, including the sun, can really mess up your scan data. At Direct Dimensions, if we are laser scanning an object outdoors we prefer to do it at night if able. Light can reflect off of your scanning object and create “noisy” data. This brings us to:
* Very reflective materials generally do not scan well. This can be avoided with a light coating of white powder spray (or anything that dulls the reflectivity). There are also some scanner manufacturers who are actively working to solve this problem.
* Fixturing: whether you are laser scanning or digitizing, it important that your scan object will not move while you are collecting data. The tiniest motion will cause inaccurate data.
* If you need hard to reach/impossible to see internal data, you should consider CT scanning or destructive slicing, both can be great ways to augment your data. (more on those later).
Moving on to 3D modeling
Now that you have a good idea of what you need to collect data, you are ready to learn all about the various ways the data can be modeled. Chapters three through five will cover, 3D Modeling, Reverse Engineering, and Inspection Analysis.
Friday, May 21, 2010
Chapter 2: Data Collection
Posted by Sara Ebright at 12:44 PM
Friday, May 14, 2010
Next week we'll be at the Rapid show and 3D Imaging Conference. Stop by booth 206 and say hello. While you are there make sure to get your very own ShapeShot taken!
If you are going to attend the conference portion of the event, don't miss our Director of Art Services, Harry Abramson, give his presentation "3D Imaging for Sculpture Conservation and Research" on the afternoon of the 18th. Harry will discuss some of our more fascinating case studies involving 3D imaging and rapid prototyping for the creation, restoration, replication, and in-depth study of fine sculpture.
See you there!
Thursday, May 13, 2010
Ancient Writing Converted to 3D Digital Form
In February of 2008, Joel Freeman of The Freeman Institute Foundation came to Direct Dimensions with an interesting project. Within his collection of historical artifacts, Mr. Freeman owns an original replica of the Rosetta Stone, the famous tablet discovered after Napoleon’s 1798 conquest of Egypt. The tablet bears an inscription of a decree by Ptolemy V circa 196 BC, written in three different languages: two distinct forms of Egyptian hieroglyphics and one form of classical Greek. The Rosetta Stone was so important in the deciphering of some hieroglyphics that the term has come to mean any document or key instrumental in the decryption of a language or code. The original Rosetta Stone has been displayed by the British Museum since 1802, but a handful of first-generation castings were made of the tablet for reproduction.
It was one of these original castings that Mr. Freeman brought to Direct Dimensions. He wants to make scaled reproductions and to help others understand the importance of this famous tablet.
His cast reproduction is full-size, approximately 38-inches tall by 30 inches wide, made from black resin with the critical lettering inscribed on the flat front face. Because it is only a face casting that is two inches deep, this posed another problem, as he wished to make an accurate replica measuring the same 11-inch thick as the original tablet.
After consulting with the engineers at Direct Dimensions about the project and understand how Mr. Freeman intended to actually fabricate the piece, it was decided that only an extremely accurate 3D digital model of this physical piece could work. The 3D data file would be used to drive a computerized industrial milling machine to carve a highly accurate mold. Direct Dimensions would have to use its most accurate and highest resolution scanning tool to capture the piece.
Over the next several days at the DDI lab in Owings Mills, the cast replica was digitized using a non-contact laser line scanner mounted on a motorized precision coordinate measuring machine, or CMM. This unique scanning system had been integrated a few years earlier by the DDI engineers for projects just like this. With the controlled motion of the CMM combined with the scanner from Kreon Technologies, this system can achieve resolutions approaching 25 microns. This translates to 3D point every one-thousands of an inch (0.001”) - a dot per inch resolution sufficient for capturing even fingerprints in 3D.
The resulting massive point cloud file was so detailed that when processed into it a 3D mesh weighed in at over 10 million polygons. A figure, according to project manager Peter Kennedy, “that definitely strained the limit of our already extensive computing power.”
In addition to the precise scan of the tablet’s front face, a model incorporating the tablet’s true thickness had to be created. With standard photographs and other reference materials provided by Freeman, the digital modeling team at Direct Dimensions used a variety of software products, including PolyWorks, Geomagic, and Z Brush, to digitally sculpt the shape and contour of the original tablet’s back side. The back was then combined with the precise data from the front to complete the high accuracy digital model of the real Rosetta Stone.
The final deliverable in polygon format will enable Mr. Freeman and his other collaborators to mill the completed replica molds. He aims to use his replica as a centerpiece in his educational programming, to be housed in an exhibit in the Black History galleries of The Freeman Institute Foundation.
If you are interested in learning more about the Rosetta Stone or owning a full-size, 3D replica, please visit www.rosettastonereplicas.com.
Wednesday, May 5, 2010
Last year we ran a feature in our monthly newsletter called "Everything You Always Wanted to Know About 3D Scanning *But Were Afraid to Ask." The 10 installment educational series covered different aspects of 3D technologies. We got such positive feedback on the series that we've decided to post an installment on our blog once a week.
Introduction: The Basics
What is a 3D model and how do you get it?
A 3D model is a digital representation of a physical object. If you already have an object, and you want it in a digital form, that’s what we do. Direct Dimensions takes physical objects that you send to us and we use advanced 3D scanning equipment to capture and transform them into 3D digital models.
We do this by processing the raw data gathered during a 3D scan into a digital model that can then be used by you for many purposes. In the next chapter, we'll cover the different methods for collecting this data, including laser scanning and digitizing. A 3D model is incredibly versatile.
Why do I need a 3D model?
3D models can be used for many purposes like making an animation or visualization. They can be used to make design changes to make a new product. They can be used to perform dimensional and comparative analysis of an object, or even FEA and CFD analysis. They can be used for archival purposes - to accurately record the state or form of an object. They can be used to digitally repair damage that has been done to an object which can then reproduce that object in its proper form using rapid prototyping and milling technologies. They can even record your face in intricate detail! (And yes, some of our lasers are eye-safe!). There are no limits as to what can be done once something has been captured in 3D.
In short, our technologies allow almost any physical object to be recreated into a 3D digital format that can be used for just about anything you want.
When? Where? How Large? What are the limitations?
With our various technologies, we can capture objects indoors or outdoors, during the day or at night. The sky is the limit for how large and we also have technology that can capture even the smallest objects. Some of our equipment is portable so we can come to your facility, or you are encouraged to ship your items to our lab.
On the large side, Direct Dimensions has successfully scanned entire airplanes, historic monuments, ships and subs, tracts of land, and large interior spaces like buildings. We’ve scanned mid-size objects like spacesuits, countless consumer products and art work. We've also done tiny, finely-detailed items like coins, medical devices, and dental appliances. We've even captured fingerprints and skin textures! The bottom line is that whatever your object, the tools exist to scan it, and its likely we use them.
Now that you know the basics of what can be scanned and how 3D data can be used, you are ready to learn more about the different methods we use for data collection!
Posted by Sara Ebright at 10:49 AM