A chip database is a compilation of individual image samples, called chips, usually measuring 256 pixels by 256 pixels or smaller. Each image section contains an accurategeocoded location and metadata, such as which sensor it was generated from, the date it was acquired, the viewing angle, and so on. These chips, can be used to collect ground control points (GCPs). You can visually match a feature in the raw image that you are georeferencing and use the coordinates from the chip database as a GCP or use the chips to automate the collection of GCPs.
With the Chip Manager, you can create new chip databases, add or remove chips from existing chip databases, and merge different chip databases. You can use the chips to collect ground control points (GCPs) on the raw images in your project. Having a chip database eliminates the need to repeatedly collect the same GCPs on imagery of the same area in a project.
The tutorial below outlines how to create a chip database using Chip Manager and how to use the chip database to collect GCPs in OrthoEngine.
Collecting Chips using Chip Manager
- Open the Geomatica Chip Manager application
2. From the Chip Manager toolbar click on File => New
3. Enter a file name and location. A new chip database (*.cdb) will be created.
4. From the Chip Manager toolbar click on File => Source Image to select a source image that will be used to collect chips from.
5. The Default Parameter Settings window appears. Specify the sensor parameters. If an orbital segment is available, the sensor parameters would be automatically extracted.
6. Click Accept
7. In the Chip Manager window click Select to choose a DEM. Once the image and DEM are loaded, chips can be collected.
8. Click New Chip on the Chip Manager window
9. Enter a unique value as a Chip ID
10. On the source image, zoom in and click on the location of the first chip. A yellow outline on the source image shows the outline of the chip that will be collected.
11. The location of the GCP (cursor location) can be changed in the Image/DEM Chip view in the Chip Manager panel.
12. Once the chip and GCP locations are correct, on the Chip Manager panel, click on the Set GCP at Cursor button, then the Extract Elevation button. Finally, click on the Save Chip button.
NOTE: To change the chip size click on Chip Size in the image viewer. The size of the chip will be reflected in the Chip Manager window and the yellow outline in the image viewer.
13. Repeat the above steps to collect the remaining chips for the project. To add chips from another image, change the source file => under File Source Image and repeat the above steps. Click on the New Chip button every time a new chip is generated, otherwise the information collected on the previous chip will be overwritten.
Using Chips in OrthoEngine
Once a chip database has been created, it can be used in the Manual GCP Collection step or Automatic GCP Collection step in an existing OrthoEngine project.
Collect GCPs Manually
1. Select Collect GCPs Manually from the GCP/TP Collection Processing step on the OrthoEngine toolbar.
2. In the GCP Collection Panel, select Chip Database as the ground control source. Afterwards, select the chip database (.cdb). The OrthoEngine ChipDatabase panel will then be shown.
Specify a DEM if applicable.
In the OrthoEngine Chip Database panel, navigate to the chip which would be the source of GCPs.
There are several options for navigating a chip database:
o Click on the # button and type in the Chip ID in the subsequent window
o Use the scroll arrows
o Type in the Chip Id in the Chip - Information section
o Click on the Search Criteria button to reduce the number of chips for selection.
- Although the GCP is located at the centre of the chip, it is possible to change the position of the GCP to another location inside the chip. To do so, click on a new point in the Image/DEM Chip Viewer of theOrthoEngine Chip Database panel and then click on the Cursor Position is GCP button.
- Once the desired GCP location is specified, click on the New Pointbutton in the GCP Collection panel. Then click on the Use Image Chip button in the OrthoEngine Chip Database panel.
- Find the same point from the Chip Database panel in the OrthoEngineViewer and click on the Use Point button to enter the image pixel and line values for that GCP. The point information section in the GCP Collection panel will be updated.
- Click on the Accept button to save the GCP.
7.Repeat the above steps until all the desired chips have been entered as GCPs. After GCP collection has been completed, close the GCP Collection panel.
Note: Select Compute Model to view the computed residual values.
Collect GCPs Automatically
- Select Collect GCPs Automatically from the GCP/TP Collection Processing step on the OrthoEngine toolbar.
- In the Automatic GCP Collection panel select Chip Database as the Control Source and select the chip database file.
- In the Images section of the panel, click in the appropriate cell under the Use column to specify the uncorrected images. Only images with an “Available” status and a computed model (“Yes” under Model) can be selected.
- The Match Channel parameter is for specifying the channel of the uncorrected image that the chips are to be matched to. This channel would then have to be similar to that of the imagery from which the chips were collected. For example, if the chips were collected on imagery that is between 0.4µm and 0.5 µm, then the Match Channel would be the one that has the closest spectral range. As such, it is not possible to achieve good match results if radar chips were applied to multispectral imagery.
5. Click on the Match GCPs button to start the matching process.
- Once the matching is completed, the table in the Chips section will be filled. The Status column indicates whether the chips were found in the uncorrected image based on the
Correlation Thresholds set (C1, C2, C3 columns). A “Pass” signifies that the chip can be found in the image. A high correlation threshold value (i.e. close to 1) shows that there is a good match between the chip and the image. A “Fail” signifies that the chip could not be located in the raw image.
Below are suggestions for improving the status from Fail to Pass:
o Adjust the search radius and matching method.
o Use another Match Channel.
o Larger chips may be difficult to match. Since the default size of a chip is256 x 256, the size can be reduced to 64x64.
o The resolution difference between the chip database and uncorrected imagery may be too great which would reduce the number of matched chips. It is recommended that there are less than 4 x differences between the chips and raw image.
7. Once the desired chips are successfully matched (Pass), click on theAdd GCPs to Project button to store the GCPs for the project.