Coastline Matching Algorithm

The preprocessing contains the following steps.

Find a map

We start from scanned maps. Later this can be extended to satellite images.

Yellow component

The color channels are decomposed, but instead of RGB, CMY is used. From the components we use the yellow channel, beacuse it is easy to detect sea, which is blue, so having only a little yellow component.

Detect coastline

In the last step the coastline is detected, using the following algorithms:

• Box filtering
• Robert's gradient
• Tresholding

Implementation details

• To create the yellow component the GIMP program was used.
• The edge detection was done by a small program written by Robert Vanyi
  • The name of this program is improc
  • The image processing operations can be done by writing scripts
  • The program can handle pgm files
  • In our case the following script was used:

    load 0 yellow.pgm	# open yellow.pgm as image 0
    load 1 yellow.pgm	# open yellow.pgm as image 1
    smooth 0 1       	# smooth image 0 to image 1
    roberts 1 0      	# create Robert's gradient from image 1 to image 0
    strech 0         	# strech the histogram of image 0
    tresh 0 50       	# treshold image 0 with treshold value 50
    isolated 0 1     	# delete isolated points from image 0
    save 0 coast.pgm 	# save image to coast.pgm
    

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