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!

3D PRINTING GOOGLE MAPS IS NOW EASY

Some weeks ago Luca Bezzi wrote an interesting post about conversion of a grey-scale image into a 3D printable .stl file, using Free Software (i.e. G.I.M.P. to convert the image and Blender, with the "Image as plane" addon). Here is a video-tutorial:

This method can be used for any image, but it is particulary useful to create physical model of terrains; in fact Luca Bezzi took inspiration from topography, as he explained in comments.

Anyway, today there is a faster and more precise method to do the same thing, as reported in Impresoras3d.com; a web-app, called Terrain2STL, that can can convert a Google Map into a 3D printable file. The app has been created by ThatcherC, is Open Source and available on GitHub.

Terrain2STL is very easy to use. You just have to type http://146.148.78.19/ on your browser; you will see a physical Google Map, and, on the right, some tools. Once you have defined the area you want to print, you can click on "Center to view" to set the center of the area (a red rectangle) on the central point of the screen. Then you can adjust the dimension of the area using the line called "Arc Second/Division". Once you have set the area, you just have to click on "Create .stl file".

A limit of this app is that you can not draw an area crossed by a grid line (in this case you will see an error message: "Something went wrong: you may be spanning a grid line"). Anyway, this problem can be easily solved dividing your area in 2 parts and saving them separately.

Opening the generated .stl file with NetFabb Basic it may happen that the danger symbol appear, because the 1st time the software may not be able to define the volume of the object; however, you can just click on the "automatic repair" button (the red cross) to easily solve the problem, and have a clear file.