The following list outlines issues to keep in mind when using targets in a project:
DO:
• Ensure the center dot of a target is large enough on all photos. The dots should be at least 8 pixels diameter in all photos. If in doubt use a larger center dot. Plan dot size based on the target that will be farthest from any camera.
• Place targets on locally flat areas, or apply a stiff backing so the targets don't bend.
• Fasten targets on the object or in the scene so that they do not move between photos - even the slightest movement between photos can throw the solution off.
• Each target should appear on 2 or 3 photos (more is better) with minimal perspective (i.e. between 50 and 90 degrees where 90 degrees is straight on to target). This is to ensure that the target will be detected and marked with a high degree of confidence.
• Ensure at least 8 to 10 targets are clearly visibility with minimal perspective in each photo and that there is overlap of targets between photos.
• Targets should have a good spread across a reasonably large area of the image.
• Targets should be in focus and not blurry. Ensure there is good exposure of all photos.
• Targets should be high contrast (i.e. avoid dark targets on a dark background) - the dot and code regions of targets should have a strong contrast and crisp edges.
DON'T:
• Don't trim printed targets too closely. You need to leave a reasonable amount of white space around the edge of the code rings or dots.
• Don’t warp or bend targets.
• Don’t use the same target number more than once.
• Don't mix target bit sets (i.e. don't use 12 bit targets along with 8 bit and / or RAD targets).
• Don't move targets between photos.
• Don't lay out targets so they are only in a line (spread them out in a wide area).
• Don't use targets that are larger than 200 pixels across in photos if high accuracy is important.