Photogrammetry at the Old Castle of Olivella

The Old Castle of Olivella stands atop a hill of the same name in the Garraf massif, in the municipality of Olivella. It is known that the castle, now in ruins, was built in the 10th century and was abandoned following the Catalan Civil War of 1462–1472.

The Barcelona Provincial Council's Local Architectural Heritage Service (SPAL), has commissioned Altiplà to prepare drawings of the Castle, as well as of the Church of Saint Peter, also in ruins, located a few meters northeast of the Castle.

The  Floor plan It has consisted of a very detailed survey, by classical topography, at a scale of 1:100 of the many wall remains that can be found. The topography of the castle's surroundings has also been surveyed.

The most complex part has been The raising of risers and sections. To obtain the wall speciation (stone by stone), photogrammetry was chosen, with some quite spectacular results.

The work procedure has been as follows:

1. Data capture using an Olympus EPL5 camera (f=17 mm) with 16.1 MP. The images were taken perpendicular to the walls, at a distance of 4 meters, and with a 60/80% coverage.
2. Adjust of each of the photographic blocks using image multi-correlation systems that allow calculating the position of each camera at the moment the images are captured.
3. Checkpoints.  They have been surveyed using classical topography. These points are introduced into the adjustment and allow us to geo-reference it and obtain residuals that indicate the geometric quality of the work. The precision is less than 1 mm, and therefore the results are very satisfactory.
4. 4.3D model. Once the adjustment is complete, a point cloud will be generated, followed by triangulation and, finally, a textured 3D model based on the images.

5. Ortho images. With this 3D model, we can generate the elevations and sections we need to carry out the delineation. The pixel size of the images is 0.001 mm, so we have more than sufficient quality.

6. Dalignment. Based on the ortho images, manual vectorization will be carried out using a CAD program, which will allow us to obtain the final document.

The final result is quite spectacular. We hope the document will be useful for archaeologists' and historians' analysis.

We thank Jordi Martínez Morales, an expert in photogrammetry, for his help.