Processing RGB Imagery into an Orthomosaic

This document serves as a guide for how to process RGB imagery into an orthomosaic for O&M Projects. Raptor Maps will continue to process all RGB imagery for Construction Projects in-house.

O&M orthomoasic flight guidelines can be found here.
Construction orthomosaic flight guidelines can be found here.

Photogrammetry Softwares:

There are many software options that allow users to create an orthomosaic from raw RGB imagery. Below is a non-exhaustive list of photogrammetry softwares along with instructions on how to create an orthomosaic using each software.

Pix4D Mapper:
Here are instructions for how to process imagery into an orthomosaic using Pix4D Mapper. Additionally, Pix4d offers comprehensive youtube tutorials with step-by-step guidance on a variety of topics.

Drone Deploy:
Here are instructions for how to use Drone Deploy's Map engine to process RGB data into an orthomosaic.
At the 6:51 timestamp, this video details how to upload imagery to drone deploy and produce and orthomosaic.

Bentley Context Capture:
Here are instructions on how to use Bentley Context Capture to generate an orthophoto (same as orthomosaic).
Here is a video with step-by-step instructions from Bentley reality capture.

Agisoft Metashape Profession:
Here is a guide for using Agisoft Metashape profession to generate an orthomosaic without the use of Ground Control Points (GCP's).

Propellor Aero

Processing Settings:

Ensure that GeoTIFF is selected as the file output format for the orthomosaic. There is no need to adjust the resolution of the orthomosaic as that will be based off of the Ground Sample Distance of the imagery.

Georeferencing:

Most photogrammetry softwares will read the metadata from the drone imagery and set a default coordinate system (typically WGS84). While it is possible to change the coordinate system, in most cases the default coordinate system will work for your project no matter where it is located in the world. Once a orthomosaic has been generated, it is possible to use a GIS software to change the coordinate system if necessary. A Raptor Maps Data Manager will notify you if a specific coordinate system needs to be used.

Sending Raptor Maps an Orthomosiac:

Email or a secure file transfer is the preferred method of sending an orthomosaic to Raptor Maps. These files should be in GeoTIFF format and include the orthomosaic as well as the tiles that make up the orthomosaic. There is no limit on the file size that Raptor Maps can accept. Files should be sent within 72 hours of when the flight took place.

Troubleshooting Incorrect Orthomosaics:

Performing a visual scan of the orthomosaic is a good way to quickly check for any obvious errors. These may be gaps in coverage or features not aligning properly, and are generally easy to spot with the naked eye. Most photogrammetry softwares will give you a breakdown of the quality of your orthomosaic based off key metrics. It is best practice to check the breakdown of these quality metrics to understand the accuracy of your othomosaic.

FAQ's:

  • Q - What is the expected files size for the GeoTIFF results?
    A - GeoTIFF files of an orthomosaic typically range from 200 MB - 5GB
  • Q - Why is my ortho look damaged with a very warped section?
    A - It is possible that a ‘junk’ image was included in your imagery. Always be sure to double check your image folders for loose shots taken before the drone has taken off.
  • Q - Can I create an orthomosaic while there is standing snow on the ground
    A - An orthomosaic can be generated when there is patchy and sparse snow on the ground, but blankets of white snow can cause issues with ortho processing. Images with sky or images containing only water can cause similar problems.
  • Q - Why cant I view the GeoTIFF file
    A - After processing, the GeoTiff may appear in a results folder attached to the project. Many results files are too substantial for typical image viewing softwares. QGIS is a software available for quickly viewing a GeoTIFF.
  • Q - Why are my results taking a long time to process?
    A - A typical ortho GeoTiff may take several hours to process at least. Increasing the amount of imagery will increase overall process.
  • Q - Why are my results spotty even though my imagery is good?
    A - Some mapping flights contain imagery with low complexity, such as plain grass. Adjusting processing options for your ortho may improve your results. Some softwares default to a ‘Rapid’ setting that is inadequate for sites with low complexity imagery.