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UAV Processing Workflow

PCI Geomatics -

This tutorial outlines the workflow for processing UAV imagery using Geomatica OrthoEngine. This tutorial shows how to import data, automatically collect tie points, extract a DEM, generate orthos and finally generate a mosaic.

For this tutorial we will be using a UAV dataset from senseFly of a quarry in Switzerland. This data was collected by a Canon IXUS 220HS camera. You can download the data from the following link: https://pcigeomatics.sharefile.com/d-s9c0c1c5827c458ab

Project Setup

Set Camera Calibration

Data Input

Collect Tie Points

Point Refinement

GCP Collection (Optional)

Residual Report

Generating Epipolar Images

DEM Generation

Generate Ortho Images

Mosaicking

Clipping Final Mosaic

Project Setup

To begin, you will need to create a new OrthoEngine project.

  1. Open OrthoEngine from the Geomatica toolbar.
  2. On the OrthoEngine toolbar navigate to File > New. The Project Information window will open.
  3. Give your project a Filename, Name and Description
    • Select Aerial Photographyas the Math Modeling Method
    • Select Digital/Video under Options
    • Select Compute from GCPs and tie points under Exterior orientation
    • Click OK

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  1. The Set Projection window will appear. Leave the boxes blank and click Cancel on this window. A popup will appear to tell you that the projection information will be read in from the first image.

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Set Camera Calibration

The next step in the process is to import the camera calibration information.  The camera calibration information for this project was calculated externally. In order to process your own UAV datasets in Geomatica you do need high-quality camera calibration to enter into OrthoEngine.

  1. On the OrthoEngine toolbar click the Set camera calibration icon

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  1. The Digital/Video Camera Calibration Information window opens.
  2. We will now import the Camera Calibration information. Included with the tutorial data is the file camera_calibration.xml. In the camera calibration window click Import and choose that file.
  3. The calibration information from that file is imported and the camera calibration window is automatically filled.
  4. Click OK

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Data Input

Now that the camera calibration is set we can input the JPEG files.

  1. On the OrthoEngine toolbar switch the processing step to Data Input
  2. Click Open a new or existing image.

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  1. Click Add Image… when the Open Image window appears
  2. Navigate to the location of the .jpeg images
  3. Select all of the JPEGs and click Open

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  1. When prompted, choose YES to import the files to PIX format

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  1. Click OK in the Multiple File selection window

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  1. The new pix files will now appear in the Open Image window

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  1. These JPEG images contain Exif tags and OrthoEngine imports these tags as metadata. Therefore, the exterior orientation (EO) is computed automatically. The following Exif tags are required for automatic computation of the EO :
    • Make
    • NominalLocation_Longitude
    • NominalLocation_Latitude
    • NominalLocation_Height
    • Acquisition_DateTime

In the case of data that does not contain Exif tags, you would need to import the exterior orientation data from a text file.

Collect Tie Points

We will now need to collect tie points in order to improve the math model and ensure that the images align correctly.

  1. On the OrthoEngine toolbar switch the processing step to GCP/TP Collection
  2. From the OrthoEngine toolbar, click the Automatic Tie Point Collection icon

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  1. In this window change the Matching method to FBM: Feature-based matching. This is a new tie point collection method that was added in Geomatica Banff
  2. For this tutorial the default parameters will be used

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  1. Click Collect Tie Points
  2. Once the collection process is complete a pop-up window will appear specifying the number of tie points that were found.

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Point Refinement

After you have collected TPs you can further refine them in the Point Thinning and Refinement window. This window allows you to automatically run thinning to remove redundant points and refinement to remove points with high RMS.

  1. Click the Point Thinning and Refinement

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  1. Leave Thin Points We will only Refine Points.
  2. Check off Deactivate images with insufficient TPs.
  3. Leave the rest of the parameters as their default values.
  4. Click Run

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  1. A progress window will appear to show the steps that have been run as part of the refinement process.

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  1. Click Accept Changes on the Point Thinning and Refinement window.

GCP Collection (Optional)

In this tutorial ground control points (GCPs) are not collected. However, when running this same process with your own datasets you can collect GCPs to improve georeferencing of the dataset. You would collect GCPs on the images using an existing georeferenced image. The automatic GCP collection process is fully outlined in the Airphoto Orthorectification tutorial.

Residual Report

From the OrthoEngine toolbar open the Residuals report icon.

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You can view the collected TPs in this window. Note the low X and Y RMS of 0.5. Additional information on the Residual Report is available from the Help.

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Generating Epipolar Images

The next step in the process will be to extract a DEM. We will first create the epipolar images and then run the DEM Extraction process.

  1. Change the OrthoEngine processing step to DEM From Stereo.
  2. Click on the Epipolar Image

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  1. For Epipolar selection, leave the default - Optimum pairs.
  2. Click Add Epipolar Pairs To Table.
  3. Change the Downsample factor to 2 – This parameter controls the number of pixels that are used from the raw images to generate the epipolar image. Changing this to 2 will increase the processing speed.

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  1. Click Generate Pairs

DEM Generation

The next step in the process is to Extract the DEM from the epipolar pairs.

  1. On the OrthoEngine toolbar, select Extract DEM automatically.

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  1. Click Select All under the Stereo pairs table.
  2. Check off the Epipolar Tracking
  3. Check off the Create geocoded DEM
  4. Set an Output file name for the geocoded DEM.
  5. Set the X and Y resolution to 41.
  6. Change the Output option to Merge.
  7. Click Extract DEM.

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* Note – When working on your own datasets can always edit the DEM using the Geomatica DEM Editing tool before generating the orthos. You can check the DEM Editing tutorial for detailed information on editing.

Generate Ortho Images

You can now generate the orthorectified images.

  1. Change the OrthoEngine processing step to Ortho Generation
  2. Click the Schedule ortho generation icon
  3. In the Ortho Image Production window click >> to add all the Available images to the Images to process
  4. Select DEM File and then Browse to the geocoded DEM that you generated in the previous step.
  5. In the DEM File pop-up window select 1 [32R] Merged DEM and then click OK
  6. Click Generate Orthos

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Mosaicking

The orthorectified images are now generated and you can create a mosaic. You can check the full automatic mosaicking tutorial for additional information on preparing, editing and generating mosaics in the Mosaic Tool.

  1. Change the OrthoEngine processing step to Mosaic
  2. Choose the Mosaicking The Mosaic Tool is then opened and the ortho images are automatically loaded in the New Project Wizard – Source Images window.

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  1. Click Next
  2. On the Mosaic Definition window set the Output file. A single mosaic file will be generated.

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  1. Click
  2. In the Mosaic Preparation window under Compute Cutlines change the Constrain parameter to Auto.
  3. Check off Sort Images
  4. Leave the rest of the parameters as default.
  5. Click Generate Mosaic - For this tutorial we will choose to generate the mosaic directly from this window. However, you can also choose Generate Preview and then further edit the mosaicking options and colour balancing before generating the mosaic as outlined in the full mosaicking tutorial.

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  1. The mosaic is shown in the Mosaic Preparation window.

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  1. Click Finish
  2. The full mosaic is then loaded into the Mosaic Tool. You can now open the full mosaic file in Focus.

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Clipping Final Mosaic

In this tutorial we are specifically interested in the quarry so we will clip out the area of interest. Provided in the data download is an AOI vector file. This will be used as the clipping layer.

  1. In Focus open Tools > Clipping/Subsetting
  2. Under Input make sure that File is the UAV mosaic.
  3. Under the Available Layers section check off all three mosaic channels.
  4. Under Output set an output file location and name.
  5. For the Define clip region switch the Definition Method to Select a clip layer
  6. Browse to the location of pix.
  7. Change the Bounds selection to Shape(s) Boundary. The shape of the actual AOI polygon will then be shown.
  8. Click Clip

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  1. You can now load the clipped mosaic file into Focus to view the final mosaic of the AOI.

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