This method uses a manual digitizer which consists of digitizing table and a host computer. The digitizing table consists of a two layer magnetized wire mesh that is sandwiched between a very flat top made of stable material and a metallic or plastic bottom.
The electrical connections are such that when the cursor button is pressed at any point on the table surface, electrical impulses are sent to the control unit where they are interpreted versus digital table coordinates of the cursor position relative to a defined origin on the table. The cursor must have at least one button for coordinate registration but usually has more-4, 24 or 16 to server various command and coding functions.
A menu box is usually provided on the table. This consists of a number of designated areas on the table where the activation of the cursor sends a particular command e.g. ‘map mounting’ or ‘digitizer configuration’. The control unit provides interface to the host computer, while the user terminal enables keyboard data and command entry plus receipt of messages from the system.
Digitizing Software must be provided to enable activation/deactivation of the system, definition of the area to be digitized, map mounting and general control of the digitizing process. Map mounting involves the computation of transformation parameters between the table and map coordinate systems via an affine transformation.
A problem with manual digitizing is slow progress for dense data e.g. contours Operator stress and fatigue which deteriorates the quality of output. Thus is no longer is use currently
Another method of manual digitizing that is common is the on-screen digitization. It entails using a scanned map or image and displaying this on the screen and using a normal mouse, the features of interest are picked and their locations recorded.
Digitization in the Raster Format
- Manual gridding
- Video digitizing