Surveying ME - BMEEOAFM201

When and why do we need to survey buildings?

• as-built plan
• reconstruction needs to be planned and the original plans are not available or not up-to-date - an example: an old floor plan with poor quality
  
• condominium establishment
• heritage preservation

Classic method (less frequent nowadays): floorplan, section, facade are developed independent 2D drawings

Modern method: 3D surveying as well as modelling, 2D drawings can be generated

Simple method:

• using a steel tape and/or Laser Distance Meter to measure distances
• using a sketch to record data - an example: 
• using an appropriate app on a smart device with Bluetooth connection -
  , for instance
• good and efficient for a simple flat, drawing is developed in a local system
• result: floorplan - an example (compare to the sketch above)

More modern method - total station:

• reference points in the building in the same system
• some detail points measured by tacheometry (total station) - an example
  
• significance of digital images taken by a total station - an example: points to measure, generated by an architect, this photo shows the points that a land surveyor has to measure, coordinate list: this is the first result of surveying, images taken by the total station of each point:  image1, image2, ...
  
• further details by tape and/or Laser Distance Meter
• result: 3D wireframe model at different levels in a local or national system - an example

More modern method - terrestrial laser scanning,

• several stations, registration into the given system using and measuring targets
• result: 3D point cloud or 3D solid model - an example

More modern method - mobile mapping -

• the instrument is in hand, in a backpack
  
• sensors are on a vehicle, like Google Streetview
• efficient, impressive but less accurate (at the moment)

Another modern method - (digital) photogrammetry

• terrestrial: images are taken from a camera
• arial: images are taken from a drone
• overlapping images, registration, relative, transformation into a given system using reference points measured by total station, professional software is required, e.g. Regard, Agisopht, Recap, ...
• result: 3D point cloud or 3D solid model with texture
• an example: image1, image2, image3, image4, image5, coordinate list of reference points, point cloud generated from the pictures using Regard3D

Steps of processing:

1. take pictures, at least 80% overlapping
   
2. add pictures
3. compute matches, et keypoints (~10k in the example above)
4. triangulation
5. pointcloud (~48k)
6. dense point cloud (~500k)
7. georeferencing: using reference points measured by the total station in order to transform the model into a given reference system
8. export point cloud