Scanning a Background Map
- Use a grid: In most cases you cannot scan the entire draft map (the background map). You are either limited by Windows (which limits the maximum size of background maps), by the available memory, or by the size of the scanner (A4). In these cases it is strongly recommended that you should draw a grid on the draft map. In many cases there is already a kilometer grid which can be used. If this does not exist, you should draw a precise grid of vertical and horizontal lines (perhaps at a distance of 10 cm). Then the scanned pieces can be easily adjusted to fit the map in OCAD.
- Resolution: As a general rule scan the map with 300 dpi.
- Scanning: If you have a scanner connected to your PC, and a 32-bit TWAIN driver is installed, then you choose the Scan command from the Background map menu to scan the background map.
If there is no TWAIN driver or you use a scanner on another PC, then use the scanner program which comes with the scanner and save the scanned background map as a BMP, GIF, JPEG or TIFF file. Choose Open from the Background map menu to open this file in OCAD. Choose Adjust from the Background map menu to adjust the background map to the grid or to the part of the map you have already drawn. It is best to use 4 grid points (arranged in a rectangle) for the adjustment. This will compensate for rotation and any distortions of the draft.
Choose this command to scan a background map on a scanner connected to your PC. To use this command a 32-bit TWAIN driver must be installed for your scanner. If no TWAIN driver can be found, you should contact the vendor of your scanner to obtain a 32-bit TWAIN driver. See Scanning a background map for tips about scanning.
- Acquire submenu: Choose this submenu to start scanning. This command will show the main window of the TWAIN driver of your scanner. After scanning a file, a dialog box is displayed where you can enter a filename for the scanned background map. Then the scanned background map is opened.
- Select source submenu: If more than one TWAIN source (or more than one driver) is installed, you can select in this submenu the desired source.