How To Scan A Building Elevation With Your SmartPhone

By Steve Bury | 25th September 2023

Introduction to Scanning With A Smart Phone

Working in the realms of architecture, heritage, and construction often requires detailed 2D CAD drawings. Though there are several mobile apps for 3D modelling, turning these 3D models into precise 2D CAD drawings can be a challenge. This blog post aims to simplify that process for you. The tutorial below walks you through using the Polycam app on a LiDAR-enabled iPhone Pro to scan a building facade and then using CloudCompare to create a 2D image that you can draw over in any CAD program. This workflow can also be used with other smart phones, but the latest iPhone Pros will usually give the best results.

Watch this video to gain a full understanding of the process. The step-by-step overview of the process set out below will help guide you when you carry out your first elevation survey.

What You'll Need To Carry Out Your Measured Survey

  • A smartphone (iPhone Pro with LiDAR recommended)
  • Polycam App (most other 3D scanning & photogrammetry apps should also work)
  • CloudCompare Software [Download Here]
  • CAD Software (BricsCAD Shape is excellent and can be downloaded for free) [Download Here]
  • A tape measure for check measurements

A Step-by-Step Guide To Surveying An Elevation With A Smart Phone

Step 1: Scanning the Facade

  1. Launch Polycam: Open the Polycam app on your phone. 
  2. Record: Press the record button and walk in front of the building facade to capture its details. 
  3. Process: Once you've captured the entire facade, hit the 'Process' button. Your 3D model will be generated.

Note: Before leaving the site, take a measurement between two identifiable points across the facade for later scaling.

Step 2: Transferring The Scanned 3D Model To Your PC

  1. Choose File Format: Select OBJ as the export file format for your 3D model.
  2. Transfer: Transfer this file to your PC using email, Google Drive, or any other method.

Step 3: Editing Your 3D Model In CloudCompare

  1. Open CloudCompare: Launch CloudCompare on your computer and import the 3D model.
  2. Orthographic Projection: Turn on the orthographic projection mode.
  3. Alignment: Use the 'Level' function to align the coordinates of your model. Pick two points on a horizontal line and a third point above the first two to align it.
  4. Trim Excess: Use the 'Clip Box' function to trim unnecessary portions of the model.
  5. Export as Image: Navigate to 'Display' and choose 'Render to File' to create an image of the model.

Step 4: Importing An Orthoimage Into CAD Software

  1. Open CAD Software: Launch your CAD software (BricsCAD Shape recommended).
  2. Insert Image: Use the 'Images and Insert' function to import the image into your drawing.
  3. Scale Image: Use the scaling feature to adjust the image to its correct size. You can either use the measurement taken onsite or the dimensions in CloudCompare for this if you’ve used an iPhone Pro.
  4. Draw Over: Once the image is scaled, use standard CAD commands to draw over it and create your elevation drawing.

Tips for Scanning Accuracy

  • The iPhone Pro with LiDAR generally gives an accuracy of +/- 2 cm over the length of a small elevations.
  • For greater accuracy, use the check measurements taken on site to rescale the image - the longer your measurement, the more accurate your survey will be.

Conclusion

That’s it! You’ve successfully turned a 3D model into a scaled 2D image ready for CAD detailing. This method is particularly useful for professionals in architecture, building conservation, and surveying, among others when an elevation drawing is needed for a small project but where high accuracy isn’t essential. Larger facades and complicated building surveys should always be carried out by a reputable surveyor equipped with survey-grade laser scanners to get results suitable for construction projects.

Call or email Bury Associates for help with larger facade surveys and other high accuracy projects.