Register Scanned Quadrangle Maps

This option creates two databases in the same directory as the scanned map image:

  1. 07AUG44.PNG : original scanned image
  2. 07AUG44.DBF: points used for registration.  You can edit this file, and redo the registration if there are problems you need to correct.
  3. tin-07AUG44.DBF: triangles used for the registration, which can be regenerated as needed from the 07AUG44.DBF file  if you change any parameters.  This is used to warp the map into a projection that Google Earth and MICRODEM can both display.

Open New imageHistoric map scan may require special considerations which you should understand

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.

  • Click "Image point" button on the bottom of the form, and double click on a corner.  The screen coordinates will be entered in the table.
  • Click "Coords" button on the bottom of the form, and type in the values (most likely in lat/long coordinates) for the corner you just clicked.
  • It is optional to type in the name of the corner, but can help you keep track of the process.
  • "Next point" button on the bottom of the form
  • Repeat entering the corner locations and corner coordinates for all 4 corners.
  Form after entering the four corners.  The NE corner, on the 4th line, in fact has an error in the LONG. 
 

 

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.

  Note that the x-spacing is over 10 times the y spacing, because the SE corner has 50 (the latitude entered twice)  instead of 1 for the longitude. After correcting that value, re-select the Quad Map button.
  X and Y spacings now almost identical.  They may not be identical, because the assumptions might not be strictly valid, and the map projection might not preserve distances, but this registration only needs to be able to identify the correct intersection on the lat/long graticule.
 

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:

  • Close MICRODEM (so you can delete files).
  • Find the files that match your scanned map
    • Do not delete the .DBF file, unless you want to lose all your work.  This is the only one the program cannot recover
    • Delete the "tin-xxxxxx.dbf" file
    • Delete the .datum file
    • Delete the .pgw file
  • You can edit the DBF file with the coordinates in EXCEL
    • Insure you have the four corners of the map on the first 4 lines, properly labeled, with correct labels.
    • Save the file as a CSV file.
    • Open the CSV file with the DB option in MICRODEM, which will convert it to a DBF
  • Reopen PNG file with the map.
  • Image, Register
  • Quad option, set the tick spacing in minutes, and recompute the interior pointsI jus.  Pay particular attention that you do not get any warnings.
  • Reg, TIN option.

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