This tutorial outlines the automatic orthorectification and mosaicking process of airphotos using Geomatica OrthoEngine. This workflow shows how to import data, automatically collect GCPs and tie points, generate orthos and finally generate a mosaic. The data used in this tutorial was captured using an UltraCam D camera and can be downloaded from the following link - https://pcigeomatics.sharefile.com/d-s9dfa06e638745ec9
When initially loading the images into Focus they appear to lie on top of each other. This tutorial explains how to process the data so that they lay in their correct geographical location.
Project Setup and Data Ingest
To begin, you will need to create a new OrthoEngine project and ingest your imagery
- Open OrthoEngine from the Geomatica toolbar.
- On the OrthoEngine toolbar navigate to File > New. The Project Information window will open.
- Give your project a Filename, Name and Description
- Select Aerial Photography as the Math Modeling Method
- Select Digital/Video under Options
- Select Compute from GCPs and tie points under Exterior orientation
- Click OK
- The Set Projection window appears.
- Enter the output projection information for the images
- Enter the pixel and line spacing
- Click OK
- On the OrthoEngine toolbar click the Set camera calibration icon
- The Digital/Video Camera Calibration Information window opens.
- Enter the focal length, chip size and Y scale factor information
- Click OK
- On the OrthoEngine toolbar switch the processing step to Data Input
- Click Open a new or existing image.
- Click Add Image… when the Open Image window appears
- Navigate to the location of the images and click Open
- When prompted, choose YES to import the files to PIX format
- Click OK in the Multiple File selection window
- The new pix files will now appear in the Open Image window
- On the OrthoEngine toolbar click the Import exterior orientation data from text file icon
- Verify the Input projection, Input angle unit and EO vertical datum information
- Enter the Accuracy information
- Click Browse to navigate to the eo.txt file for the dataset
- Select Import. You will notice the GPS/INS information for the images is saved
Now that the images are imported, you can collect GCPs and TPs.
- On the OrthoEngine toolbar click the Collect GCPs Automatically button
- Change the Control Source to Georeferenced Image and browse to the reference Image.
- Browse to the DEM file.
- Click Match GCPs.
- Once the procedure is complete the collected GCPs will be listed in the Collected GCPs panel
- Click Compute Model to view the residuals for each of the GCPs
- If required you can change the Search Options and recollect GCPs. You can also select which GCPs you would like to use from the list of collected GCPs.
- To remove a GCP from the model calculations simply click on the checkmark in the Use as GCP column.
- Once you are satisfied with the GCPs in the list, click Add GCPs to Project. You can rerun the GCP collection after adding to the project to collect more GCPs.
- Close the GCP Collection window.
Collect Tie Points
Since there are multiple images, we will collect tie points in order to further improve the model. In the last year PCI has been working to improve the accuracy and speed of tie-point collection by up to 20%.
- From the OrthoEngine toolbar, click the Automatic Tie Point Collection icon
- Browse to the DEM file.
- Leave the other parameters as defaults. Similar to the GCP collection you will likely have to change the collection options based on your dataset. Open the Geomatica Help to read about each of the options
- Click Collect Tie Points
- A pop up will appear to tell you how many tie points were collected. More or less tie points will be collected based on how much overlap is available in your dataset.
- You can change the Options and collect more tie points if required.
- Close the Tie Point Collection Window
Refine GCPs and TPs
After you have collected GCPs and TPs you can further refine them if required.
- From the OrthoEngine toolbar open the Residuals report icon
- The collected GCPs and TPs are displayed in this window. There are quite a few options in the window. Explanations of each of the Options are available in the help.
- If you have any points with very high residual errors you can remove them from the model using the Delete Point button
- Once you are satisfied click Compute Model and then Close the window
Generate Ortho Images
You can now generate the orthorectified images.
- On the OrthoEngine toolbar switch to the Ortho Generation processing step and select the Schedule ortho generation icon
- In the Ortho Image Production window select the images in the left panel and add them to the right panel
- Browse to the output location for your ortho images
- Select the DEM
- Modify any of the default parameters to suit your data
- Click Generate Orthos
Once the ortho step is complete, you will have orthorectified images. You can use these images to create a mosaic. Please refer to our in depth mosaicking tutorials for more information: automatic mosaicking and manual mosaicking.
- On the OrthoEngine toolbar switch to the Mosaic processing step and select the Define mosaic area icon
- In the Define Mosaic Area panel, click Browse
- In the File Selector, select the output file name and location for the mosaic file
- Click OK
Generate a Mosaic
- On the OrthoEngine toolbar click the Automatic mosaicking icon
- In the Automatic Mosaicking panel modify the color balancing method and cutline selected method to best suit your imagery.
- Click Generate Mosaic
- Once your mosaic has been generated the following window will appear. Click OK.
- To view your mosaic, load the file into Focus.