The Leica Airborne Digital Sensor (ADS40/80/100) is a line-scanning sensor that collects long strips of images. This camera can simultaneously collect panchromatic, color, and color-infrared stereo imagery. All multispectral bands are collected simultaneously at the same high resolution, providing five-band, co-registered, and equal resolution imagery from data acquisition.
The following tutorial outlines the orthorectification process of ADS imagery using automatic tie point collection and the input of surveyed GCPs.
Project Setup and Data Ingest
To begin, you will need to create a new OrthoEngine project and ingest your imagery. ADS Level 0, Level 1, or Level 2 imagery is associated with a support file, typically found in a SUP folder. Before you use any of your ADS imagery, make sure the referenced file names are specified correctly in the support (*.sup) file: IMAGE_FILE_NAME, ORIGINAL_ORIENTATION, ADJUSTED_ORIENTATION (Optional), ORIGINAL_CALIBRATION, LEVEL_0_NAME
- 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 ADS under Options. The Exterior orientation will be set to Automatically determined
- 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.
- Click Add Image… when the Open Image window opens.
- From the file selector window select the .sup file for each of your images.
- Click Open
Collect Tie Points
In this project we have two images that we wish to orthorectify and then mosaic. Therefore, we will want to collect tie points. Tie points identify how the images in your project relate to each other. You can collect both tie points and ground control points to compute a transformation to improve the fit between the images.
- From the OrthoEngine toolbar, open the Automatic Tie Point Collection window
- Leave the other parameters as defaults. You may 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.
Refine Tie Points
After you have collected TPs you can refine them as required.
- From the OrthoEngine toolbar open the Residuals Error Window
- The collected 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
- Click Compute Model to recalculate the model after removing any points
Add surveyed GCPs from text file
A GCP is a point with known ground coordinates used to determine the relationship between an image and the ground. With ADS imagery, the GCPs must originate from a ground survey. You can import a text file of GCPs from another source, such as those obtained from a ground survey.
- Click on the Collect GCPs Manually button
- From the Open Image window, open one of your images as the working image
- On the GCP collection window switch the ground control source to PIX/Text file
- Click Select PIX/Text File and open your GCP text file
- On the Read GCP from Text File window select the format of your text file. A format is a string representing the order and the contents of the fields. In this case our GCP file is in IXYE format (I: GCP Identification, X: geocoded X coordinate, Y: geocoded Y coordinate, E: GCP elevation). You can check the help to better understand the GCP text file formats.
- Click Apply Format
- If the list of GCP points looks good click OK
- The GCP Text File window will open. Select your first GCP and click Transfer to GCP collection panel.
- You will notice that the GCP coordinate information is loaded into the manual collection window
- On your working image the location of the GCP is shown. Click Use Point to add the image pixel and line values to the manual collection window
- Once all the information for the GCP is filled out click Accept
- Repeat steps 8-11 for each of the GCPs in the file.
- The GCPs all appear in the Accepted Points section of the collection window. In order to calculate the residuals, as shown below check the compute model box at the top of the window
- Once you have finished entering the GCPs for your first image close the image window.
- You can now open your next image from the Open Image If the GCPs for this image are in the same text file you can repeat steps 8-11 for this image. Otherwise, close the GCP Text File and open the new text file. Follow steps 4-11.
- Once GCPs are entered for all the images you can close the GCP collection window.
Generate Ortho Images
Now that the TPs and GCPs have been collected you can 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.