Ortho Image Production using AgiSoft PhotoScan

PhotoScan is a software of choice to produce quick orhtos. Here is the workflow that I follow to produce ortho rectified mosaics quickly.

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PhotoMosaic mosaicing

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PhotoMosaic is a module of PhotoMod(lite) software suite. I use this software to stitch ortho-rectified individual tiffs and create a ortho mosaic.

  • It can align images precisely at the overlap area to avoid ghosting of features.
  • Second reason is that it is very good at color balancing adjacent rectified tiffs.

 

 

 

 

Note: I extend my thanks to PhotoMosaic software for providing demo/lite version. This helped me to create very professional looking mosiacs.

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I have been working on Image Processing field since 2006. During those years I have worked on numerous projects and faced interesting problems related to image processing. I have learned several interesting approaches to solve those problems. Recently I realized that I can host my bog for free. This was a wonderful opportunity to keep record of my findings. This way I won’t forget the details of what I did exactly to solve a particular problem. Initailly I started writing these articles for myself, but with time my objectives changed from simple record keeping to the following:-

  • Keep a presentable record of interesting/intuitive methods that I discovered, related to ortho-rectification of aerial imagery.
  • Would like to show how I handled various image processing challenges.
  • To be more transparent about my professional work.
  • To present the apps that I have created (using VB.net etc.) to improve efficiency of numerous tasks in the ortho-rectification work flow.
  • Create short tutorials related to ortho-rectification software (e.g. ArcMap, MicroStation, PhotoScan, PhotoMosaic etc.

 

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