Turning GeoTIFF into TIFF + worldfile (QGIS)

hi all,

after some weeks I go on with the videotutorial from the Project Tovel. Until now we saw how to download some Open Data for our GIS, how to load georeferenced raster level in QGIS, how to georeference historical maps.

Today I will show something particular, that probably many of you will not need very often working on landscape archaeological project, but that will be more important to manage excavation GIS: how to turn a GeoTIFF picture into a TIFF + worldfile image.

As some of you will know a GeoTIFF is a particular kind of raster data in which the georeferencing values are embedded within the TIFF itself. This option can be a nice solution for a topographer but it is extremely annoying for archaeologists. The reason is simple: topographers often work on pictures or maps that are ready to be used, without the necessity of any photo-editing, which (on the contrary) is an important phase in archaeological photo-mapping process (e.g. for the "Aramus method"). The primary difference between a GeoTIFF and a TIFF + worldfile image is that it is not possible to modify the first one without loosing the georeferencing values (which are integrated in the picture), while it is possible to perform some photo-editing operations (change the colors, balance the brightness and contrast, etc...) in the second one, without problems, being the geolocalization data stored in a separate file (the worldfile).
For this reason working with raster images and worldfile is often the best choice for archaeological GIS (especially for excavation), where it can be useful to "erase" all the part of the photo which are outside the area of interest (e.g. outside the rectification region) and to take advantage of transparency in overlapping different raster levels (which can correspond to different stratigraphic levels).
As I wrote previously, the videotutorial I prepared using the data of Project Tovel simply shows how to turn a GeoTIFF, currently the unique option for QGIS georeferencing module) into a TIFF and a worldfile, a more useful format, without exiting the software.

Have a nice day!

How to take pictures for photomosaics in narrow conditions: A clever solution for a common archaeological fieldwork problem.

Everyone who works on archaeological excavations knows situations like this:

A narrow and deep trench or a wall near to the limit of the excavation area.

If subsequently we have to make a photomosaic of the profile or facade, it means:

• either photographing from the top, hazarding the consequences like distorsion:
  
  
  
• or splitting the photomosaik in numerous single tiles, and that means a lot of work!
  

A very simple and clever solution for this problem can be the use of a mirror:

Putting it down in an inclined position on the ground and positioning yourself on the opposite side (watch the illustration beneath and heed me kneeing outside of the trench), it allows you to take a shot of the reflection of your facade in the mirror.

Of course the picture will show the object mirror-inverted, but don't worry:
The rectification software will fix it again...

Thanks a lot to Granma for borrowing us her wonderful kitsch bedroom-mirror!

Cloud distance tool.

I was working on different SfM/IBM of a grave we dug in 2010. we have the documentation of four different levels (see picture below). It was a complex archaeological context, with two skeletons buried in different times (double burial), both partially destroyed by the construction of the Renaissance apse. Moreover the tomb was built on the side of a prehistoric house.

I tried to rectify the point clouds inside CloudCompare v. 2.4 (normally i use GRASS with the ply importer addon or MehLab) and I discover this fantastic tool: compute cloud/cloud distance. It can calculate the distance between two different overlapping mesh, similarly to the GRASS command "r.mapcalc". As you can see in the pictures below, the distance analysis between the first and the last documentation can represent the quantity of removed ground. It could be really useful for analysis of damages in buildings.

first point cloud

fourth point cloud

cloud/cloud distance

cloud/cloud distance over the fourth point cloud