When you collect the tie points:
- Choose features that you can identify accurately at the resolution of the raw image.
- Select features that are close to the ground. Features that rise above the ground, such as buildings, may appear to lean in the image. Therefore, a point collected from the top of a feature in one image may be displaced from the same point collected from the top of same feature in another image.
- Avoid using shadows as tie points. Although shadows may be easy to see in the image, they are not permanent and can move from one image to another.
- Beware selecting common or repetitive features such as parking lots or lines on a highway. When you try to identify the feature in the image, it may be easy to select the wrong one.
- Select some tie points that appear in three or more images. Tie points that join multiple images together produce a more accurate model.
- If available, enter the elevation value of the tie point in the Tie Point Collection window. Tie points with an elevation value help to control elevation and improve the accuracy of the geometric model.