Simple calibration

Open again a test image in 'UVMAT_DEMO_FILES/EX01_pair'. We shall use the diameter of the half cylinder visible on the upper let of the image to set the calibration. Its physical diameter is 2cm. The corresponding diameter in pixels can be obtained with the ruler displayed by the menu bar Tools/ruler of uvmat.

First zoom on the cylinder to optimize the precison. Select zoom on, press the left mouse button and adjust the field with the directional key board arrows. Then unselect zoom on to allow for other mouse actions (otherwise zoom has priority). It is also useful to increase the contrast at the cylinder edge by setting MaxA to 100 in the frame Scalar (right side of uvmat).

Then select the menu bar Tools/ruler, press the left hand mouse button on the cylinder edge, draw a diameter keeping the mouse pressed, release it on the opposite edge. The length in pixels, 140, is displayed, so the scaling factor is 140/2=70 pixels/cm.

Open the menu bar Tools/geometric calibration. A new GUI geometry_calib appears on the right side. Activate the upper menu bar Tools/Set scale on this GUI and introduce the value 70 in the edit box which pops up, and validate with OK. A set of calibration point coordinates appears in the table [ListCoord] of the GUI.

To see the calibration points on the image, first display the whole image by unselecting fix (tag [CheckFixLimits]) in the frame Coordinates of uvmat. Then press PLOT PTS in geometry_calib.