How To: Digitize from an Image



Steps to digitize an image in the background.


1. Obtain a Windows BMP file of the image you want to digitize from. You can use a graphics utility to convert most standard raster files to BMP.

2. Use th BMPDIS command to convert the BMP file to display list (DIS format) of colored polygons. This file is not registered, but it can be displayed in ARCPLOTW, ARCEDITW, ALLOCATW or ROUTEW using SCREENREST.

Depending on the original BMP file, a DIS file may be quite large and a little slow to display.

3. Start ARCEDITW and run the following commands:

MAPEXT 0 0 100 100

This will set up the screen and the map extent some legitimate but arbitrary values (0,0,100,100). You can use any map extent you wish. You can use the WHERE or DISTANCE commands to make sure the display is in the correct map extent.

4. Run SCREENREST to display the DIS file created above. For example, if the display file was called dispfile:


5. Run the CREATE command to create a coverage and digitize tics off of the image.

CREATE mycover

This is a crucial step and you must do it very carefully. You must only digitize tics for which you have actual, accurate map coordinates. These are locations that you have actual coordinates of the final map. These tics will be used to transform the map to the correct coordinates.

You can use the local/pan zoom capabilities of ARCEDITW, to zoom into an area of the image, to get more accurate positions for the tics.

6. You may now continue to digitize other features of the map (arcs, labels etc). At any point, you can redraw the screen by using the following steps:


When you digitize from the back drop image, you must always have the map extent set to the values originally set in step three, otherwise the back drop image will no longer match the coverage you are digitizing. If you leave the editing session, you must reset the map extent again to the original values when you come back.
{NOTE{You can use the local/pan zoom capabilities of arceditw to zoom or pan into a particular to get more accurate digitizing.
7. When you are done editing, run CLEAN or BUILD on your coverage in the usual manner.

8. At this point, a coverage of tics, needs to be created with the true map coordinates. Each of these tics will have the same user-id as the tics found in the digitized coverage (mycover). There are two ways this can be accomplished:

i) Use CREATE to create tic cover using the digitized cover.

CREATE finalcov mycover

Then go into tablesw and edit the x and y locations of the tics so they match the true map coordinates.

ii) Use GENERATE with the TICS subcommand to create a coverage with the correct tic ids and locations.

9. Run TRANSFORM on the digitized coverage and the coverage created in step 8 (finalcov).

TRANSFORM mycover finalcov