Most sensors are rectangular with varying aspect ratios, or linear arrays of pixels. Some of the rectangles are well known industry standards (2/3",1/2", etc). Area scan cameras are the rectangular arrays of pixels, line scan cameras are a single line of pixels.

To eliminate any confusion associated with orientation of object vs. orientation of sensor, the smaller dimension (usually vertical) is used as the framing dimension. If conditions are such that the imaging of the object is marginal, and your sensor is rectangular, you will have the option of picking up a little extra coverage by orienting the object horizontally.

Select the format of your camera if it is one of the listed standards, or check "other" and fill in your sensor's dimensions, or line scan length in the box.