Register Scanned Quadrangle Maps
This option creates two databases in the same directory as the scanned map image:
Zoom to 100% for best results. You might be able to work at 50%, but you must be careful about the resulting loss of accuracy, particularly if you already reduced resolution from the original map scan.
Pick Register Image from the menu. If the map has a cutout in a corner, make sure your "corners" are on the intersections of two parallels and two meridians.
On image registration form, register the four corners of the map.
The quad map button on the right side of the form should now be enabled; select it. Set the size in minutes for the ticks (e.g. 15' for a 1:250K quadrangle map) or the grid lines present on some maps. The map margins should have labels for the ticks or grids, from which you can compute the spacing, but they might not be in all corners. After you enter the tick spacing, check the results for the NW and SE corners of the map, and the approximate pixel spacing in the horizontal and vertical directions. If the x and y spacings are substantially different, you might have a problem with the corner coordinates. The program will provide an error message if your corners do not define two parallels and two meridians; you should not ignore that warning.
Select "Next point" option.
Double click on each lat/long grid point intersection on the map. The image coordinates will be entered, as will lat/long from the rough registration. You can only select the grid intersections, and the coordinates will be rounded to the nearest value from the tick interval. The program will automatically advance to the Next Point. You should select points in a consistent pattern so that you get all the intersections.
If you need additional points along the edges (for instance because you have a conical projection which has been cut to have a rectangular map region), you can use a gazetteer to register additional points or the Tri--triangle extrapolate to the edges to add points along map edges.
When done, perform a Reg File button, and pick the TIN Mapping option. The program will create a Delauney triangulation registration with several graphics to help evaluate the registration.
Scanned AMS 1:250K quad of western Europe done after World War II
Neat lines are not parallel or straight, and the map cannot be easily registered.
Coordinates are listed on the edges of the map.
Notice that all the intersections line up in rows and columns, and that no points have been missed.
|Options on the REG button after doing Delauney triangulation registration||
Problems with the registration:
This example does not consider datum shifts. Historic maps do not indicate the datum used, and at the map scale (each pixel is about 36 m in this example) and with allowable cartographic license, it was not worth considering. That additional step could be used if warranted.
Last revision 2/24/2014