Importing ground-truth points

Before you can perform a classification or an accuracy assessment, you must have ground-truth data: information collected on location. With ground-truth data, image data can be related to real attributes and materials on the ground. By collecting ground-truth data, remote-sensing data can be calibrated, which aids in the interpretation and analysis of what is being sensed.

With supervised classification, the ground-truth data acts as a training set, which is used by the learning algorithm to generate a classification model. In Object Analyst, you collect training samples for both the supervised classification and accuracy assessment in the same window.

After you select the file, layer, and field you want, you can opt to apply a rule to manage any conflicts that may occur. That is, a conflict occurs when two or more points in a polygon have different classes. You can select from three rules to manage any such conflicts:

None: Take no action to resolve conflicts; that is, do not import ground truth to conflicted objects.
First: Import the first-encountered ground-truth point for conflicted objects.
Majority: Use the ground-truth value occurring most frequently as the value to import for conflicted objects.
If necessary, you can adjust the minimum percentage threshold. By doing so, objects below the threshold are not updated.

Note: When there is no majority; for example, if four classes are at 25 percent, or when the majority threshold you specify is not met, None is applied.

To importing ground-truth points

In the File box, type or select the layer you want.
If the file is not in the list, click Browse, and then select the file you want.
In the Layer list, select the layer with the ground-truth points you want.
In the Field list, select the classification field you want.
Beside Sample type, do one of the following:
- To use the selected class for training, make sure Training is selected.
  When you view the class name in Attribute Manager, it is prefixed with _T.
- To use the selected class for accuracy assessment, click Accuracy Assessment.
  When you view the class name in Attribute Manager, it is prefixed with _A.
To manage any conflicts that occur, in the Conflict-resolution rule list, select one of the following rules:
- None
- First
- Majority
  When you select Majority, you can, if necessary, type or select the percentage weight you want in the box to the right. The default value is 51.
Click Import.
A message appears, showing the point layer you selected and the number of one-to-one matches that occurred, and the number of conflicts.
After you complete importing the ground-truth points, return to setting up Training Sites Editing.