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(Created page with " This tutorial explains the steps I use to prepare scanned drawings in Gimp for use in building an aircraft model. Drawings are not usually scanned perfectly straight, are no...")
 
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This tutorial explains the steps I use to prepare scanned drawings in Gimp for use in building an aircraft model.
===== This tutorial explains the steps I use to prepare scanned drawings in Gimp for use in building an aircraft model. =====


Drawings are not usually scanned perfectly straight, are not always perfectly square, and are not always 100% accurate.  I use the following steps to ensure my drawings give me a solid start on my model, to reduce issues later on and improve overall accuracy.
Good quality models start with good quality drawings, but even the best drawings have issues.  Some are not 100% accurate or do not represent production specs, or are not quite square.  Even if they are absolutely perfect, issues can be introduced during scanning.  Despite our greatest attempts to scan them straight, they are never 100% perfect.  I use the following steps to ensure my drawings give me a solid start on my model, to reduce issues later on and improve overall accuracy.


# Crop out each individual drawing
I will be using the development of the Canadair Tutor for this tutorial (how appropriate).  I use Gimp for my graphics work, but the general techniques can be used in any photo editing software.  I have installed the Rotate/Crop plugin.  I am starting with some scanned 3-view drawings with cross sections, and some reference photos that are roughly orthogonal.
# Straighten using the Straighten and Crop plugin
 
# Check squareness of symmetrical drawings and fix if necessary using the Shear tool
# We will start with the top view as length and wing span are more precise than height:
# Duplicate any one-sided drawings such as cross-sections
[img]http://flightgearcanada.altervista.org/wiki_files/Tutorial1_01.jpg[/img]
# Extend any cross section location markings into the inside of the aircraft
 
# compare to reference images to find inaccuracies.  Note that images will always have some perspective errors, this needs to be taken into account when comparing with an orthogonal drawing. Photos taken from a greater distance will have less distortion than those taken closer.
In this case the top view is at 45° on the sheet, but even if it is "straight" we will still try to straighten it perfectly in this step.
# For plan view, set the crop tool aspect ratio to the same as the known aircraft length/span, then select the plan view and crop tight to the extremeties of the wings/nose/tail
 
Select the Path tool and click on a point at each end of the marked center line.
[img]http://flightgearcanada.altervista.org/wiki_files/Tutorial1_02.jpg[/img]
 
Zoom in and place each end of the path more precisely.
[img]http://flightgearcanada.altervista.org/wiki_files/Tutorial1_03.jpg[/img]
 
Select Tools -> Transform Tools -> Straighten and Crop.  If it is a 45° rotation, set Crop after rotating to "No crop".  Click "Ok"
If part of your drawing has been clipped off, you can either drag it into the middle or select Image -> Fit Canvas to Layers.
The nose of the aircraft should be pointing to the left, if it is not then rotate it using Image -> Transform menu.
 
# We will now ensure the drawing is square.  Duplicate the layer and set the transparency of the top layer to 50%.  Flip the top layer and move it so that the center line of the top view lines up with that of the bottom layer.  Fine tune the position of the top layer until it most closely matches the bottom layer.  In this case, there is some slight blurring on the outer wings and tips of the horizontal stabilizers, but it is pretty square overall.  Since it is close, I will use this image as is with both layers showing, and I will run the outline of my model down the middle of the lines where there is some slight blurring.
[img]http://flightgearcanada.altervista.org/wiki_files/Tutorial1_03.jpg[/img]
 
# Next we will check for accuracy of the drawings by comparing it to a reference photo.  Open the reference photo as a new layer on top of the drawing layers and set its transparency to 50%.  Scale and move the image until its outline lines up with that of the drawing.
Owenpsmith
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