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How to cut and merge images

This was released as a necessary practice in the Microstation and clip_image002Manifold recent course I taught, here I present the summary of how:

I have an image download from Google Earth that I had georeferenced and want to cut it based on a polygon that represents the extension of the urban perimeter of a human settlement. Then I want to merge it with a grey scale image I have, that has lower resolution but should be a single image keeping the colors to the front.

clip_image004In this case I’ll use Microstation Descartes, which is equivalent to AutoCAD Raster Design or what we knew as Overlay. If there are not visible Descartes tools it should be done “tools / toolboxes” and there the panel “Descartes raster Control” must be turned on.

1.Cut the image based on the polygon.


Once I have the polygon, I use the “corridor images” command; it asks me the cut polygon so I select it by clicking over yellow shape.

Then when doing a second click, a screen is displayed that asks me:

  • Which of the reference images I want to cut
  • The target path
  • Image format
  • If I want transparency in cut leftovers
  • And the output pixel size.

clip_image006By default it put to me the pixels size which has the image but I can change them.

clip_image008Then appears a message in the corner informing that it is processing and at the end the reference image is displayed. In the result it can be seen that has been cut the image color and the rest is transparent so I can see the image in grayscale back.


2. Merging both images

Now what I want is for both images convert into one, so I make a shape of the area I want to merge, and use the “merge images” button. It asks me the same as in the previous command, except that in this case I do not show any pictures each, but rather the “average” option to choose both.

clip_image011And ready gentlemen, look how wonderful, it has made an image with both.

Ah, to do this, there is no need to have a Descartes or Microstation license, since the disc which Bentley sends if you enter their page in the Select CD option gives you 15 minutes… what I have done has cost me 11.


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