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Generate Contour Lines from Image

Jan 10, 2011 at 6:06 PM

I can get an image of the Wisconsin elevations as contour lines. Is there a way to generate a vector layer from that image?

 

Jan 10, 2011 at 7:02 PM

It can sort of be done, but I'm not sure I'm recommending our system for this, since our raster to vector is more or less untested and returns boxy rectangular edges from raster content.  I would not recommend trying to convert black lines per say into a vector.  That might not work as well as you like, and in the end you probably want a polygon with the fill area representing the elevation area, not really a line.  In truth, most raster to vector, even when you have the good stuff (programs with licenses running in the thousands annually) you are usually looking at something that is partially supervised.  If it is a one time deal, my recommendation is to load up the image, and then manually go through and create the lines or polygons that you want using the shape editor, using the underlying image as a guide.  The only way any kind of automation would be preferable is if you wanted to do this for thousands of images.  In such a case it might be worth creating a custom script to handle the color coding and conversion for you, but you would probably need optical character recognition to read the elevations themselves.  For even hundreds of images, the time it will take you to manually digitize the lines is much less than the time required to develop code smart enough to do this automatically, or even to fix the half-completed supervised raster to vector stuff.  The best results from a raster to vector situation come if you color code the polygon areas.  Most DRG files that show contours have lots of other stuff on there though, and that would interfere.  But presuming you had the image form with nothing else but the lines, you could use a flood fill on the areas between the lines.  When you run our Raster to Vector tool, this would create separate polygon regions though you would probably have to go through afterwords and fill in the attributes with the elevations you needed.

 

Ted