Ortho Rectification using MicroStaion (TerraPhoto & TerraScan)

A step-by-step guide on how to create Ortho-mosaic using TerraPhoto & TerraScan.

Microstation is a CAD software and I use TerraPhoto and TerraScan modules from terrasolids.com to create ortho rectified mosaics. 
In this article I will discuss the steps I follow to ortho-rectify aerial imagery acquired by our (RSSL) imaging system. [spacer height=”30px”]

 We need several pieces of information to get started:-

  • GPS navigation information.

We have inertial navigation system installed on aircraft. It records planes location i.e. XYZ, yaw, pitch & roll at a very high frequency(200 Hz). GPS records navigation info in binary foramt, so we need to convert it to text format in order to use it in TerraPhoto & TerraScan.

  • Images for the required area.

We have 4 separate multi-spectral cameras installed in aircraft (cessna 206) i.e. NIR, Red, Green, Blue. Each camera stores grey scale images and we need to stack these images together to create false color composite.

  • Image name Vs GPS time.

Imaging system communicates with the GPS (via com port) and records very accurate GPS time for each camera click.  Later on during post processing, imaging software uses these accurate time stamps to create image name vs gps time file. This information is needed in TerraPhoto for overlaying images at correct position & orientation.

  • Trajectory.

It is the path followed by the camera, while images were recording. This file is created from GPS navigation data.

  • Camera calibration file.

This file contains default lens distortion correction parameters, camera location w.r.t inertial measurement unit, image dimension etc.

Camera Calibration parameters