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Help > Building a 3D Model > Creating and Modifying Objects > Object Points > Sphere Target Marking > Sphere Target Guidelines
Sphere Target Guidelines

 

        Ensure the sphere targets are firmly fixed in the scene and cannot move/roll between photograph captures.

        Ensure the background is not the same color as the spheres themselves. The whole background does not need to contrast with the sphere but most of it should.

        The image of the spheres should not be overly large in the photos (up to 1/50th of the image size in pixels)

        Use sphere targets that are solid in color (i.e., no pattern on the sphere), and matte (so no bright specular reflections).

        Use sphere targets that cannot be easily deformed. For example, soft foam balls or squash balls may depress against a hard surface under the force of their own weight and warp, and therefore may not be a consistent shape across all images.

        Use sphere targets that have smooth surfaces. For example, a tennis ball has a coarse and jagged surface (from the fuzz) which results in noisy edges and therefore less precise marking.

        Use sphere targets with flat lighting to ensure that there are no specular reflections on the sphere target nor strong shading (half the sphere in shadow for example). A specular reflection can appear in different positions depending on the camera angle, and this can confuse the detector.

        Examine the red outline of the detected ellipse after the sphere has been marked. A problem with the sphere detection can often be seen in how this red outline matches the edge of the sphere image. In the case of a poor fit, delete the mark and re-mark it by ensuring that the region tightly encompasses the sphere with little extra background.