Manually stitching a Map from scanned images with GIMP

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zamzon
Posts: 55
Joined: Sat May 28, 2005 12:45 pm

Manually stitching a Map from scanned images with GIMP

Postby zamzon » Thu Jun 22, 2006 3:00 am

If you are not satisfied with results of PanaVue or another Panorama Stitching program, do it manually:

1. Install Gimp and the GTK (http://www.gimp.org/downloads)

Both have a (Windows) Installer. Please use >= 2.3.9
Be aware: When using multiple monitors, the user install windows might open on wrong one.
Select as much memory for GIMP as possible, when you have big maps. 2-3 times the raw pixel size (x*y*3)

2. Scan the map

Define pieces as big as possible and a little overlapping, but leave some margins, where the map doesn't lay flat on the glass because of the frame. To avoid a manual croping step, assure, that the whole scanned picture is usable and has no ugly/black edges or corners.
When actually scanning, try to always align at one edge of the glass frame, to avoid angles between the map tiles.
To get an overlap at the middle of a big folded map, make another long horizontal fold on the next coordinate grid line of the map.

3. Load the parts of the image

Start Gimp, create a new image with aproximately the size of the resulting picture (change it later with Menue Image/Canvas Size).
Immediatley delete the background layer, to save memory (select it in the 'Layers, .. Dialog' and click Trashcan)
Use File->Open as Layers... from the image window for loading the scanned tiles.
In the Open dialog, select all the components of the map (or just the parts belonging to the border, when you are not sure, that your PC has enough memory and repeat this, when saved the previous work). To load click on the first image, then shift-click on the last one to select everything in between; or control-click on individual images to add or subtract them) and press 'Open'.
Save often! Gimp is not the most stable program in the world, especially with big pictures. Save it in gimps own xcf-format to keep the layer definitions.

4. Built the final Map

Arrange each Image's Position by moving it with the mouse. For cursor key movement it must be selected in the 'layers dialog' or with page up/dn. Zoom in and out with +/-. Move mode is with 'm'.
Start with the border tiles of the map by aligning the printed outline of the tiles at the gimp window border by moving them and checking with scrolling horizontaly and vertically. When the border is done, move the inner parts.When the map has a grid, concentrate on it.
It will never be perfect, when you used a consumer scanner. Forget about it. You'll not going to do a moon landing with this map.
But if you want to make it really good, then it might be needed to rotate the tiles, which are to twisted to much, again starting with the outer tiles. Rotate mode is shift+r (set the small black point to the rotation center, or enter its coordinates).

5. Save final Map

If you are satisfied with the alignment, use Save Copy to create a BMP-File to be loaded in Map-Manager.
You'll never have to remove the layers. So you can always resume the work and recreate an improved map.
If your memory is not enough for creating a copy (gimp gives error message or crashes), right click on a layer in the layer dialog, select 'combine all visible layers' and then save to a bmp file and also keep the untouched .xcf file.

Happy stitching..

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