Stanford Digital Forma Urbis Romae Project

Notes on Forma Urbis Models

Because of the errors in 3D scanning some of our models have a number of artifacts that can give false impression about the original fragment. This page shows examples of these artifacts. Click on the thumbnail preview to see a larger image.

Well-aligned models

Fragment 313
This image shows a well-aligned model. Notice the clarity of incisions, presence of fine detail and a general clean appearance. This model can be trusted to examine fine detail of the fragment, such as guidelines.

Most of our models can be viewed with our ScanView viewer. For a small subset of the models, we are also providing PLY files, which can be viewed using Scanalyze.

Blurring artifacts

Fragment 376
As the fragments get larger, errors in alignment create blurring artifacts. Notice that the fragment has an overly smooth appearance, the incisions are not clear, and some incisions have artificial double lines.
Fragment 376
Although you cannot trust the fine details on this fragment, such as depth of incisions, the models are still useful for looking at large-scale features such as clampholes and overall incision patterns.
Fragment 376 top
In the cases where the complete models are overly blurry, we provide a finer resolution model of just the top of the fragment. This model should be used solely for close up examination of the fragment's incisions.

Noise artifacts

Fragment 37l
Another artifact arising from bad alignment is noise in the models. This has the appearance of bumps and craters of various sizes on the surface of the model, and in particular along any sharp edges. Notice the bumpy appearance of the fragment on the left.
Fragment 37l detail
Closeup of the right edge of the model shows the characteristic "bumps" that are due to noisy scans. These bumps are not part of the original fragment.
Fragment 619a
Here is another examination of noisy misalignment artifacts. Notice a bump along the edge of the fragment and the sprinkling of extrusions from the surface. A similar bump along the edge is sometimes present even in well-aligned models, where it is due to edge curl in the vripping process


Fragment 137
When the surfaces that are being scanned are too dark or occluded, the laser scanner does not return any data. As a result you may encounter holes in our models.
Fragment 010f
To make our models more visually pleasing, we have filled the smaller holes with an artificial surface using an automated process. Most of the time, this holefilling is unnoticeable to the user and does not create any false impressions about the original fragment, since the artificial surface follows the geometry of the model. However, when a particularly large hole is filled, a smooth piece of surface is created that may be very different from the original fragment. The image on the left shows a hole from an iron bar filled with a smooth surface. These artifacts are particularly easy to spot and ignore since the holefilling surface is a lot smoother than the geometry that surrounds it.

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Natasha Gelfand, 4/1/2004