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Extract building corners fast and precise with X-ray function

Karst is a beautiful region of Slovenia, most famous for a long list of natural and cultural heritage wonders. Bora-swept region is home to a unique subterranean landscape, like the famous Postojna Cave and the Škocjan Cave, Lake Cerknica, one of the largest intermittent lakes in Europe, Lipizzaner horses, red wine and very specific architecture.


An architecture company was contracted to make a survey map of a rustic villa for the purpose of establishing cadastral boundaries and Historical Restoration of the villa which contained several courtyards and external walls. This layout is very common for karst architecture. Outcome data needed to allow complete 1:1 replication of original architecture.

The Problem

Several courtyards and cracked old walls made this project extremely complex. It was difficult to measure and collect all the appropriate number of points needed for high-quality data which would later allow for proper restoration and documentation.

Taking the traditional approach with total station was extremely time consuming and complex (due to number of points measured and the fact that total station needed to be moved around). It did not provide enough quality data and the level of accuracy that was expected.


Due to the challenges they had with accuracy and number of points to be measured, the architectural company decided to try (for the first time) a completely new approach for them. They contacted the 3Dsurvey team to help with completing the survey map with a drone and 3Dsurvey software.  For the purpose of this project, Marko and Vid (3Dsurvey Team), went on the field together with the architect. They took pictures of the location and Villa with the drone so that they could later process all the data in the office.


In only 2 hours, the team had taken 617 images in 3 flight missions with the Phantom 4 RTK. First mission was a top-down mission to secure good images of the rooftops. In the second mission they chose “double grid”. This is used to take images from multiple sides and suitable for flying closer to objects so that it captures more vertical details. Third mission was done in manual mode to collect additional images of the critical parts of the house for better detail.

To achieve survey grade accuracy, 5 special 3Dsurvey Ground control targets were used. These GCPs are automatically located on images during the processing stage.

In addition, to properly and accurately measure building corners, the function called X-ray was used. An X-ray orthophoto is created which allows the user to draw walls without even measuring them.

Project tools and specs:

Drone: DJI Phantom 4 RTK

Number of images: 617 images (4 flight mission; 3 using DJI flight app, 1 manual)

Area of interest: 150m x 120m.

Field survey: 2 hours. 2 persons involved

Location: Village Sveto, Slovenia


The processing part is always done in the office.  For this project It took less than 1 hour for images and telemetry to be imported into the software. Next step is orientation, where user needs to orientate automatically recognised ground control points with GNSS measurements. This is all that needs to be done for the reconstruction step which creates a highly detailed 3D point cloud model.

X-ray orthophoto

Creating an orthophoto map of the walls was the next step in the process. Instead of manual line drawing and trying to find the correct points which follow the wall lines and corners, the team used the latest feature of 3Dsurvey, X-ray.

This feature automatically creates an orthophoto map of the walls, by recognizing groups of vertical points and identifying them as the walls of the building. This orthophoto is displayed with white lines. Where there are more ‘vertical’ points, the stronger the white color is. Where there are less vertical points, or ‘horizontal’ points, the more transparent the white color is. So the resulting image looks like an X-ray. Hence, the name.

X-ray makes walls visible on the map through the rooftops and it can later be draped on the digital terrain model. Boundaries are simply drawn using CAD tool with minimal effort, decreasing the amount of time needed to draw the lines 10-fold. It also increases accuracy of the project.


  • 3D model in OBJ format – standard 3D format
  • Orthophoto map in JPG and KMZ ready for Google Earth 
  • CAD lines in DXF


  • 10 x Faster and easier drawing of walls and corners for survey map
  • No need for additional measurements with total station on the field
  • More accurate comparing to traditional approach with total station.

Want to know how you can do this in practice? Watch the on-demand webinar.