Chapter 7: Load a Background Map
Open: Choose this command to open a background map which is displayed as a background picture on the screen. OCAD can open BMP, GIF, JPEG and TIFF files. In addition OCAD maps (*.ocd) or encrypted OCAD maps (*.eocd) can be opened.
Manage: Choose this command to set options for displaying and printing the background maps. The Background Maps Manage dialog box is displayed. This is a non-modal dialog box. It is possible to switch between the dialog box and the map window without closing the dialog. Changes are directly updated in the map.
- V (Visible): Activate this option to display the open background map(s).
hintHint: To hide all background maps temporary use Hide in Background map menu.
- F (Visible in Background Favorites view mode): Activate this option to display the background map if Background Favorites view mode is set.
- Dim: Select here a percentage to make the background map appear brighter. 0% means the background map is displayed in its original colors. 100% means the background map appears completely white. Dimming is used to get a better distinction between the background map and the map.
- T (Transparent): Activate this option if more than one background map is open and if you want them to be transparent.
- Hide: This command is activated if one or more background maps are open.
Choose this command to temporarily hide the background map(s). Choose this command again to make the background map(s) visible. If you want to hide only one background map open the dialog box Background Maps Manage. Within this dialog deactivate the visibility in the column V for the desired background map.
Assign to spot color
(This function is only available in OCAD Professional!)
This feature is used in a special production process. It is a process to update old hand drawn or scribed maps. The printing plates for each spot color are scanned (black and white or gray-scale) and then used as background maps. When such a background map is assigned to a spot color, it is displayed in the color of that spot color. In addition, when spot color view is activated the background map is displayed together with the corresponding spot color. Note: This feature is intended for black and white or gray-scale background maps. If a color background map is assigned the resulting colors are undefined.
- B (Blockout):
(This function is only available in OCAD Professional!) This field is only available for raster background maps. Activate this field if the background map is a black/white blockout mask. The blockout mask blocks out lower background maps.
File In this field the file name appears.
- Move Up: Click this icon to move the selected background map upwards one line.
- Move Down: Click this icon to move the selected background map downwards one line.
- Open: Open a new background map.
- Relink: Relink background maps to another directory.
- Remove all: Click this button to remove all background maps. It doesn't delete the background map files.
- Remove: Click this button to remove the selected background map. It doesn't delete the background map file.
Use a Georeferenced Raster Map as Background Map
If your map is georeferenced and you want to use a georeferenced map as background map:
- Select Open in the Background Map menu. The Background Map dialog box opens.
- Select a file and click OK.
The grid map will then be positioned correctly in the selected coordinate system. You can skip the remaining steps in this chapter and start drawing immediately.
- hint Click the Entire Map button to display the entire background map.
- hint The Draft Mode option in the View menu can be used to dim map objects and the background map itself.
- hint OCAD files can also be loaded as background maps.
- video available Background Map Basics
Use a Non-Georeferenced Raster Map as Background Map
If your map is georeferenced and you want to load a non-georeferenced map:
- Select Open in the Background Map menu. The Background Map dialog box opens.
- Select a file and click OK.
- Enter a resolution for the background map and click OK.
The background map is displayed at the center of the current drawing area. The raster map (background map) now needs to be aligned with the map. In other words, it needs to be referenced with the map coordinate system.
hint You can scan a raster map for use as a background map directly from OCAD: Select Scan in the Background Map menu then choose the Scan submenu. Your scanner's dialog box will open. Interactive Alignment of the Background Map (Georeferencing) The easiest way to do this is to align the intersection points of the raster map's coordinate grid with those of the map. A maximum of 12 point pairs can be used.
- hint If the size of the raster map corresponds exactly with that of the map scale and has not been rotated, it is possible to align it with the map using a single point pair. OCAD will correctly reposition the raster map without changing the scale or angle.
- hint If the raster map is contorted, rescaled or rotated, you will need to use between 3 and 12 point pairs to align the image with the map. OCAD repositions the raster map by transforming it (affine transformation) and adjusts the scale and angle accordingly. The point pairs should be distributed equally across the map.
To align the raster map:
- Display the coordinate grid in the drawing window.
- Select Adjust in the Background Map menu.
- Click the first point of the point pair, i.e. the intersection point of the coordinate grid on the raster map.
- Click the second point of the point pair, i.e. the intersection point of the coordinate grid on the map.
- Repeat steps 3 and 4 for all point pairs and finish the alignment process by pressing Enter. The background will be repositioned.
- hint If the alignment point pairs lie outside of the drawing window, you can move the map section between the alignment point pairs.
Once you have completed the map alignment, the raster map can be saved as a georeferenced raster map. The advantage of this is that the raster map will be loaded in the correct position the next time it is opened.
To save the raster map as a georeferenced raster map:
- Select Export in the File menu.
- Select the raster format you want (TIF, JPG, GIF or BMP)
- Select a Resolution (300 dpi is recommended for printing maps)
- Select the Create World file option
- Click OK
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.
Adjust the Map to the Background map
This command is active when a background map is displayed. If more than one background map is open a dialog box is displayed where you can choose the desired background map.
Choose this command to adjust the background map to the grid or to the part of the map you have already drawn. It is highly recommended to draw a precise grid on the draft map and then to use the crossing points of the grid for the adjustment (however, any points can be used for the adjustment). The grid button must be pressed to see the grid. You can use 1 to 12 points for the adjustment. For each point you do the following:
- Mark the grid point on the background map.
- Mark the same grid point on the grid displayed on the screen.
When you have adjusted enough points, press the Enter key on the keyboard. The background map is rotated and stretched to get the best fit for the adjustment points. You can achieve a precise adjustment with 4 adjustment points arranged in a rectangle. This way you can compensate rotation and distortion. The horizontal and vertical scales will be adjusted individually.
Select Transform from Map menu
- Move ADD
- Stretch / Shrink ADD
- Mirror ADD
- Rotate Map ADD
- Change coordinate System ADD
Affine (Map menu)
- This function was called Transform Map before OCAD 10.2.3
Choose this command to adjust the whole map on background map or on grid. With this function you can geo-reference the map. The grid button must be pressed to see the grid. You can use 1 to 12 points for the adjustment. For each point you do the following:
- Mark a point on map.
- Mark the same grid point on reference (background map or grid.
When you have adjusted enough points, press the Enter key on the keyboard. The map is rotated and stretched (Affine transformation) to get the best fit for the adjustment points. You can achieve a precise adjustment with 4 adjustment points arranged in a rectangle. This way you can compensate rotation and distortion. The horizontal and vertical scales will be adjusted individually.
- This function is only available in OCAD 10.2.4 and later
Choose this command to adjust a part of the map on a geo-referenced background map. The Rubbersheeting Transformation dialog box appears.
- Define rubbersheeting perimeter: Click the Define button and define the perimeter by drawing a polyline on the map. To define a new rubbersheeting perimeter click the Remove button to remove the actual one.
- Add rubbersheeting points: Click the Add button first and then click 2x on the map for each point: (1) Mark a point on the map. (2) Mark the same point on the reference map. The rubbersheeting points are shown on the map by a red and a green cross and a connection line.
- Calculate transformation: Calculate the rubbersheeting transformation: Click the Transform button.
hint Click the Undo button if you are not satisfied with the rubbersheeting transformation. hint Uncheck rubbersheeting points in the Used column if they should not be included in the transformation. Unchecked rubbersheeting points appear in gray color on the map.
Center Map to Drawing Area Choose Transform in Map menu - Center Map to Drawing Area. This function is often used to center a map drawn in OCAD Professional edition into the smaller drawing area from OCAD Standard or CS edition. OCAD moves the map offset, all objects, all background maps and all bookmarks. After this function the map is still geo-referenced. In the dialog the extent with the existing map offset is shown in grey, the extent with the new offset in blue. The green rectangle shows the drawing area of OCAD Professional edition (80x80m), the orange the drawing area from Standard edition (4x4m). If a map should be visible in all OCAD editions then the entire map must fit in the 4x4m drawing area.