In addition to image coverage, the other key consideration in the
planning of any survey is how the texture of the target will resolve
in individual photographs. Automated feature matching relies upon
the ability of computer algorithms to identify unique
corresponding features in overlapping photos. For good results, any
effects that reduce textural variability within images or increase
feature variability between images should be minimized during
acquisition. Common issues preventing algorithms from resolving
coincident points include homogeneous surface texture, changes in
the target, and changes in illumination. The latter two have the
same effect of making a unique feature appear differently between
images, although both require different strategies for reducing the
deleterious effect on model construction. Poor or variable image
texture is often due to surface reflections, flat surfaces with little
textural variation, and the occurrence of deep shadows. The target
itself may appear to change between images due to wind shifting
vegetation, or the movement of people and vehicles. Changes in
illumination can result from accidental shading by the photographer,
changes in the sun position, or filtering by clouds. Strategies
for circumnavigating these issues in structural studies are outlined
further in Section 5.2.
In addition to image coverage, the other key consideration in theplanning of any survey is how the texture of the target will resolvein individual photographs. Automated feature matching relies uponthe ability of computer algorithms to identify uniquecorresponding features in overlapping photos. For good results, anyeffects that reduce textural variability within images or increasefeature variability between images should be minimized duringacquisition. Common issues preventing algorithms from resolvingcoincident points include homogeneous surface texture, changes inthe target, and changes in illumination. The latter two have thesame effect of making a unique feature appear differently betweenimages, although both require different strategies for reducing thedeleterious effect on model construction. Poor or variable imagetexture is often due to surface reflections, flat surfaces with littletextural variation, and the occurrence of deep shadows. The targetitself may appear to change between images due to wind shiftingvegetation, or the movement of people and vehicles. Changes inillumination can result from accidental shading by the photographer,changes in the sun position, or filtering by clouds. Strategiesfor circumnavigating these issues in structural studies are outlinedfurther in Section 5.2.
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