The invention relates to a
user interface (300) for measuring an object viewed in an image computed from image data, the
user interface comprising an image unit (310) for visualizing the image data in the image, a deployment unit (320) for deploying a caliper (21) in an image
data space, a scaling unit (330) for scaling the caliper (21) by a scaling factor in a direction in the image
data space, a translation unit (340) for translating the caliper (21) in the image
data space, and a caliper unit (350) for visualizing the caliper (21) in the image, wherein the caliper (21) comprises a knot for measuring the object, and wherein the object is measured based on the scaling factor. The caliper (21) comprising the knot, which determines the shape of the caliper (21), is a simple reference object of known geometry and size. Looking at the image data and the caliper (21) visualized in the image, the user may easily place the caliper (21) in the image data space and adjust its size to match the size of the measured object. Unlike the prior art methods, which are based on selecting two points and measuring the distance between them, there is no need to change the view of the image data in order to place and / or adjust the size of the caliper (21). Therefore, the caliper (21) of the invention typically reduces the amount of manual interactions needed to measure the object. Advantageously, the caliper (21) of the invention also enhances the
visual experience of the user. The size of the caliper (21) may be isotropically or anisotropically adjusted, i.e. in one or more directions, by rotating a mouse wheel, while the mouse translations may determine the location of the caliper (21) in the viewing plane.