Photogrammetrical Survey with UAV

The most spread application of drones is the acquisition of images or videos from unusual perspectives, i.e. from the sky. Depending on the application field, these sensors can serve different scopes: in Cultural Heritage field it is possible to evaluate the conservation state of artistic buildings and architectures, developing 3D models. Moreover, if the drones are equipped with thermal sensors, the surveyor knows if there are problems linked with the humidity and infiltrations in the roofs

Another example regards the environmental field: the drones can help to control the pollution, radioactivity and contaminations of risk areas. Vulcanic areas, landslides, avalanches, floods, fires, mining explorations, hydrogeological instability can be monitored by UAVs instead of put in danger operators and workers. In the event of natural disasters the rescuers have the clear understanding of the situation and can organize the aids. In agriculture, drones are used to create the NDVI (Normalised Difference Vegetation Index) maps that helps the farmers in understanding if their plants are suffering or if they are sick.

DUOMO DI MILANO

In 2009 there was the necessity to create the 3D model of the Main Spire of Milan Cathedral for maintenance purposes. Since there was some problems with other technologies (laser-scanner), it was decided to plan a photogrammetric acquisition using a remote controlled helicopter with a camera.

The outcome of the survey is a set of images that needed to be orientated manually using a photogrammetric software. The orientation of the images consists in finding homologous points (more than 3, but it is suggested at least 20) on the images.

At the end of the photogrammetric process, it was necessary to draw on the images a wireframe model, and then transform it into a 3D model, building the surfaces and volumes between the wires.

Difficulties:

•Piloting an helicopter between the spires;

•Respecting a geometry of acquisition suitable for photogrammetric purposes;

Orienting manually a large number of photos.

The work evolved in the years and today, 2020, the survey of the Cathedral is complete. The last part surveyed was the main rooftop. In normal condition it was almost impossible to obtain a precise survey with no interference, because the main rooftop is crowded of tourist 7/week, 365/year.

In July 2020, during the lockdown, it was possible to fly a small drone and get a precise and high resolution survey of the roof.

The survey was performed using the DJI Spark drone.

BORGO CROPPOMARCIO (VCO)

During the Summer School of 2013, organised by the 3DSurvey Group, we studied the contribution of inclined images. The inclined images permit to capture and reconstruct also the facades of the buildings. In the architectonic surveys, if the buildings are very close one to the other, it is mandatory to perform some flights, tilting the camera towards the facades. If the camera can’t capture all the buildings it is necessary to complete the survey from the ground, using the terrestrial photogrammetry or laser scanning techniques. Also in this case the topography campaign is fundamental to register together the data captured from different sensors.

In the gallery below, three examples of the deliverables that can be obtained from a complete aerial photogrammetric survey: an high resolution orthophoto that can be “converted” into a detailed map, showing the height of the buildings by means of the shadows, and a virtual flight through the dense point cloud obtained from the photogrammetric data elaboration.

The virtual flight through the dense point cloud obtained from the photogrammetric data elaboration

Achille C, Fassi F, Mandelli A, Fiorillo F. Surveying cultural heritage: summer school for conservation activities. Appl Geomat. Published online May 24, 2018:579-592. doi:10.1007/s12518-018-0225-3

EBOLI, SALERNO – SINERGIA PROJECT

The SINERGIA project was aimed at monitoring the health of the vegetation over a whole year. It is possible to understand the health of the vegetation using particular maps called NDVI (Normalised Difference Vegetation Index). These maps are obtained interpolating the RGB and IR values captured by the images. To have a clear situation of the suffering zones of the vegetation it is important that the maps, recorded and produced month by month, are correctly aligned one over the other.

Moreover, it is possible to derive some other 3D information from the survey. In fact, the dense point cloud obtained from the matching of the images permits to sample measurements that are relevant in the agriculture field: 1.the section of the trunk 2.the distance between the rows of plants 3.the height of each plant 4.the leaf volume.

MONTECALVOLI, PISA

In 2015, after a long period of heavy rain in Tuscany, some landslides began to move towards the inhabited centre of a small village near Pisa. We were asked to perform a survey of the landslide. The 3D model obtained with the drone survey was helpful to prepare a landslide containment system avoiding further damages to houses.

SANTA BARBARA BELL TOWER, MANTOVA

In 2012, there was a strong earthquake that affected the northern Italy, producing a lot of damages to historical buildings. Especially the bell towers were in danger of collapsing and it was not safe for the firemen to reach that buildings and verify the stability.

The survey with the drone and the 3D model obtained via the photogrammetric method, permitted to design the structural reinforcement interventions without accessing the bell tower.

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