The present invention provides a method using a non contact Z height laser scan sensor to measure/detect an object surface containing extruded shapes with different Z axis elevation heights to determine the position where to precisely inkjet print outline contours, legends, logo images, or solid fill with materials. The apparatus consist of a printing carriage, a supporting beam, a printing platen for the object to be placed and a control system. The said printing carriage is installed with print heads and a laser Z height scan sensor. The object with uneven Z height surface elevation features to be printed is placed on the printing platen. The said printing carriage with the laser Z height scan sensor will scan across the object on the X and Y axis to detect the exact target positions of the uneven Z height surface elevation contours on the object. The image processing program can then calculate a precise position to print a given image, or compute an image from the contour shapes to be printed on the object. The method can be featured with high degree of automation, easy control and accurate positioning, so as to improve the inkjet printing quality.