QGIS Time Manager, for archaeological drawing on RTI-like raster series

Hi all,

I go on today writing about the Time Manager plugin of QGIS we saw in our last post. 

This time I will focus the attention on one of the alternative (and unconventional) use we can do of this tool for archaeological aims: an archaeological vector drawing based on RTI-like raster series.
Of course, when I speak about archaeological vector drawing, I mean a GIS based technique (like the one described in this old post). We already developed a little bit further this methodology in order to use it in a semi-automatic way for archaeological finds (related post 1 and 2; bibliography here), so that this post can be seen as an integration of that work-flow. For the concept of RTI, I suggest you to read +Rupert Gietl 's post about a large scale case of study for such an application and my post about the open source tool developed by Giampaolo Palma (Visual Computing Lab of the CNR-ISTI).
The concept of RTI-like raster series is pretty simple: if in a common archaeological excavation is planned an RTI documentation (e.g. to further analyse particular artefacts such as small pottery fragments, coins, inscriptions in stone, etc...), than it is also possible to use some of the original pictures (with different light conditions) to simulate an RTI viewer within any GIS software. Once one of this picture has been rectified (and georeferenced, when needed), the related worldfile can be used also for all the other images (considering that they have all the same size), so that in QGIS it is pretty simple to create a raster series through the Time Manager plugin.
The video below shows the result of this operation on a pottery fragment from the excavation of Khovle Gora, an archaeological mission in Georgia which we supported for the University of Innsbruck (Institut für Alte Geschichte und Altorientalistik).

I hope this post will be useful, have a nice evening!

WebRTIViewer

Hi all,

I write this post to complete the one +Rupert Gietl did regarding Large Scale Reflectance Transformation Imaging. As you read in that article, Rupert, using +GRASS GIS, re-built virtually the necessary light conditions to process an RTI image of an entire archaeological area. 

This is just one of the test we are carrying on with RTI techniques, since we are trying to evaluate this methodology under different aspects. Obviously, during our experiments, we encounter interesting researches carried on by other institutions. 

This post regards one of the projects we found on our way (I will write soon about other related works) and, more precisely, a software to share RTI images through internet: WebRTIViewer. Actually the source code of the application, an HTML5-WebGL viewer, is release under the therms of the General Public License 3 (GPL 3) on the website of its author: +Gianpaolo Palma.

Here is an example of its application, using Rupert's data of the archaeological site (better visualized here). To see it, just turno on the light and, holding the left button, move your mouse around.

The software comes with two binary tools (one for Windows 32 bit and the other for Windows 64 bit), which are necessary to prepare the RTI images for the viewer. For this reason I wrote to Giampolo Palma to ask if there would be the possibility to insert WebRTIViewer and the other applications in ArcheOS (to do this we would need the access to the source code of the binary tools, called webGLRTIMaker) and he kindly answered that he likes the idea and he would agree, but before to release the code of the webGLRTIMaker under an open license he will ask the opinion of his labs colleagues (the Visual Computing Lab). This institute, part of the Italian CNR-ISTI, is the same that develops other nice Free/Libre and Open Source (FLOSS) software, usefull in archaeology, such as MeshLab, which is often in our post, or 3DHOP (soon a post about it). Hopefully, if everything goes well, we will have another nice tool to add to the ArcheOS software selection, helping Cultural Heritage professionals in sharing data through RTI technologies.

Here below you can see again webRTIViewer in action (better visualized here), this time with data coming from the archaeological excavation of Khovle Gora (in Georgia), where we work for the University of Innsbruck (Austria) and support technically the fieldwork directed by Dr. Walter Kuntner of the Institut für Alte Geschichte und Altorientalistik.

Arc-Team tries Large Scale Reflectance Transformation Imaging (RTI)

With the data, collected during our mission presented recently in the post „@MAP“the Arc-Team Mobile Mapping Platform, we've tried for the first time to apply a method called Reflectance Transformation Imaging (RTI) on landscape:

Aerial Photo of the project area taken from Arc-Teams Drone

„RTI is a computational photographic method that captures a subject’s surface shape and color and enables the interactive re-lighting of the subject from any direction. RTI also permits the mathematical enhancement of the subject’s surface shape and color attributes. The enhancement functions of RTI reveal surface information that is not disclosed under direct empirical examination of the physical object. (...) RTI images are created from information derived from multiple digital photographs of a subject shot from a stationary camera position. In each photograph, light is projected from a different known, or knowable, direction. This process produces a series of images of the same subject with varying highlights and shadows. Lighting information from the images is mathematically synthesized to generate a mathematical model of the surface, enabling a user to re-light the RTI image interactively and examine its surface on a screen.“ (http://culturalheritageimaging.org/Technologies/RTI/)

We've used the processing software and viewer of Cultural Heritage Imaging, their RTIBuilder software is made available under the Gnu General Public License ver. 3.

http://culturalheritageimaging.org/IMAGES/lintel_specular_split_detail.jpg

RTI is usually used for objects of small or medium size beause of the difficulty or impossibility to illuminate whole structures or even areas / landscapes.

At this point GIS comes to our aid:

Starting from a DTM it's easily possible to create shadow reliefs with GRASSGIS' module r.shaded.relief. 

The highlight of the module in our case is the capability to modify the altitude of the sun in degrees above the horizon and the azimuth of the sun in degrees to the east of north. 

In this way we could produce artificially the needed data for our RTI-landscape attempt. 

The next step was to export from GRASS a set of 60 images with different lighting positions creating an imaginary light dome around the object:

At this point we reached the first bottelneck of our approach:

Usually, you include at least one reflective sphere in each shot. 

The reflection of the light source on the spheres enables the processing software to calculate the light direction for that image. 

So we had to create and copy in every image a fake sphere with the reflection corresponding to the sunlight direction choosen in GRASS.

It was a stiff piece of work!

At the end everything was ready for processing the images in RTIBuilder. The single steps in the software are very easy to execute and well described on the ProcessingGuide. 

We've just had some problems with the size of our images (8200x6500 pixels), which the software couldn't process, but maybe it was because of the age of our hardware...

After reducing the image-size everthing worked fine...

At the end, after installing also RTIViewer, we've held in our hands an interactive scene of an archaeological site of nearly 10.000m² which is almost invisible from the ground.