This tutorial outlines the optical satellite orthorectification process using OrthoEngine. This workflow will show how to import data, collect GCPs and tie points and then orthorectify the images. Kompsat-3 data of Toronto, ON will be used for this tutorial, however these same steps can be followed with other types of satellite data.
The following steps are completed in this tutorial:
- Project Setup
- Setting the GCP/TP Accuracy
- Collect GCPs
- Collect Tie Points
- Refine GCPs and TPs
- Generate Ortho Images
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 Optical Satellite Modelling as the Math Modeling Method
- Select the appropriate modelling method under Options. More information on each of the model types can be found in the Geomatica Help: http://www.pcigeomatics.com/geomatica-help/concepts/orthoengine_c/MathModels_Optical_explain.html
- Click OK
- The Set Projection window will appear. Click Cancel on this window. A popup will appear to tell you that the projection information will be read in from the first image.
- On the OrthoEngine toolbar switch the processing step to GCP/TP Collection.
- Click Open a new or existing image. Since Kompsat-3 data is directly supported we do not have to ingest it first. You can check the supported sensor list to see which data can be directly opened in Geomatica.
- Click Add Image… when the Open Image window opens.
- Navigate to and select the key file for your sensor. For Kompsat-3 data you need to select the Aux.xml image (K3_20130501182829_05101_19871327_L1R_Aux.xml) from the File Selector window. For other types of data, you can search the Geomatica Help for the sensor name to determine which file you need to use to open the image.
- When prompted, choose to add the MS bands and import the data file to PIX.
- Also choose yes when asked to create overviews.
- Your new pix file will now appear in the Open Image window.
- Repeat steps 8-11 for the other image (K3_20130501182829_05101_19871328_L1R_Aux.xml)
- If you wish to pansharpen your imagery you can do that before orthorectifying. You would need to also add the PAN band for each image through the Open Image window. You can then Pansharpen through OrthoEngine (Tools > Merge/Pansharped Multispectral Image).
Setting the GCP/TP Accuracy
Prior to collecting GCPs and TPs you’ll want to verify and adjust the GCP/TP Accuracy settings for your project. Setting the proper accuracy values is very important. If your project consists of surveyed GCPs, the accuracy entered should be sub- metre. More information on setting the accuracy of GCPs and TPs is found in the Geomatica Help.
1. On the OrthoEngine toolbar expand the Tools menu and click GCP/TP Accuracy…
The GCP/TP Accuracy window appears
2. Depending on whether you want to set the accuracy of GCPs, TPs, or both, enter the value by which you want to set the accuracy of the GCPs and TPs in the Pixel, Line, Elevation (Z), Easting (X), and Northing (Y) boxes, as applicable.
3. Click OK.
Now that the images are imported, you can collect GCPs and TPs. The following section of the Geomatica Help outlines the minimum number of GCPs to collect for each type of OrthoEngine math model: https://www.pcigeomatics.com/geomatica-help/concepts/orthoengine_c/Chapter_55.html.
- 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.
- For this example the Search Options will be left as their defaults. However, these will likely need to be changed for other datasets. You can click on the help button to bring up the Geomatica Help. Each of the options are outlined in this document.
- 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 we have two images and we want to ensure that the two images match each other, 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, open the Automatic Tie Point Collection window.
- 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 Error Window.
- 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.
- You can switch to look at the GCPs, TPs or Both.
- When you click on one of the points in the table you can see the residual summary for each image.
- 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 step and select the Schedule Ortho Generation button.
- 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.
- Click Generate Orthos.
Once the ortho step is complete you will have two 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