The IDLgrVolume::ComputeBounds procedure method computes the smallest bounding box that contains all voxels whose opacity lookup is greater than a given opacity value. The BOUNDS property is updated to the computed bounding box.
            Syntax
            Obj->[IDLgrVolume::]ComputeBounds [, OPACITY=value] [, /RESET] [, VOLUMES=int array]
            Arguments
            None
            Keywords
            OPACITY
            Set this keyword to the opacity value to be used to determine which voxels are included within the bounding box. All voxels whose opacity lookup is greater than this value will be included. The default value is zero.
            RESET
            Set this keyword to cause the BOUNDS keyword of IDLgrVolume::Init to be reset to contain the entire volume.
            VOLUMES
            Set this keyword to an array of integers which select which volumes to consider when computing the bounding box. A non-zero value selects a volume to be searched. The default is to search all loaded volumes. For example: VOLUMES=[0,1] will cause ComputeBounds to search only the volume loaded in DATA1. 
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