The error estimates are accuracy weights of the position and orientation parameters. The estimates have two functions:
- To define the lower and upper bounds of the position and orientation parameters.
- To automatically weight the exterior orientation (EO) data with ground control points (GCP) and tie points (TP) during aerial triangulation (AT).
Accuracy weights of the position and orientation may have already been provided from the Global Positioning System (GPS) or an inertial measurement unit (IMU) system, but if they haven’t, you need to estimate them.
When the EO is considered accurate, smaller error estimates should be applied.
- For example, you can apply estimates for x, y, and z as 2,2,2 and estimates for o, p, and k as 0.1,0.1,0.1. These error estimates would allow plus or minus 2 meters of movement from the original position values, and plus or minus 0.1 degrees of movement from the original orientation values.
For EO that is considered less accurate larger error estimates should be applied.
- For example, you can apply estimates for x, y, and z as 15,15,15 and for o, p, and k as 5,5,5. These error estimates would allow plus or minus 15 meters of movement from the original position values, and plus or minus 5 degrees of movement from the original orientation values.
The orientation error estimates for omega and phi should never exceed 5 degrees, and the kappa error estimate should not exceed 10 degrees.
To determine an error estimate for the kappa value
- In CATALYST Professional Focus, open an aerial image.
- On the Maps tab, right-click New Area, and then click Properties.
- In the Area Properties dialog box, click the Projection/Extents tab.
- In the Rotation box, enter the kappa value corresponding to the image.
- Click Apply, and then click OK.
- Compare the rotated image to a basemap or a geocoded reference.
- Provide a rough estimate of the difference between the north in the image and north in the geocoded source.
To determine the position (x, y) error estimates
- In CATALYST Enterprise, orthorectify a small subset of the data set.
- In Focus, open the orthorectified images.
- On the File menu, click Export to Google Earth.
- Measure the difference in position (x, y) of landmarks between the orthorectified image and Google Earth to determine error estimates.
You can make changes to the error estimates at any interval of the AT workflow.
To make changes to the error estimates
- In CATALYST Professional OrthoEngine, open the OrthoEngine project file (oe.prj).
- In the Processing step list, click Data Input, and then click the Manually edit exterior orientation data button.
- In the Manually Edit Exterior Orientation Data window, under Exterior orientation table, do one of the following:
- To make changes to an individual image, in the Image ID column, click the ID of the image you want, and then proceed to step 4.
- To make changes to all of the images, click Select All.
- Under Edit Selected Images, in the boxes beside Accuracy, enter the error estimates, as applicable.
- Click Apply Accuracy, and then click OK.
- On the File menu, click Save.