SD39

[NW Modeling List]

James:

If you don't get a direct (easy) answer to your question, then you could use a technique called photogrammetry to figure out the lettering size.  (We'll use a really simplified version of photogrammetry, do don't get too scared.)  You will need a scale drawing of the loco and a set of vernier calipers to do this.

Using your scale drawing and calipers, determine the height of the door panels the lettering is on.  Measure their height on the scale drawing with the calipers, and using the drawing's scale factor, calculate their "real life" height by multiplying the measured height by the scale factor.  For example, suppose the door height on the drawing was 0.850", and the drawing you are working from is HO scale, or 87.1 to 1.  Multiply 0.850" [drawing inches] x 87.1 [drawing scale factor] and get 74" [real life inches].  Aha-the door is 74" tall!  (Note:  I didn't do this for the SD39-this is just a fictional example!)

Print out the photo you have-the print-out scale doesn't matter all that much, but bigger will enable you to be more accurate.  However, life is MUCH simpler if you can find a photo taken from far away, and exactly perpendicular to the side (or end) of real life loco or other object you are interested in.  (Although a ¾ view is artistically more interesting than a direct side-on view, it's much less good for estimating dimensions of features on the loco.  So modelers would be better off taking a telephoto lens along and shooting locos from side-on and end-on perspectives from a far distance as well as the "artistic" perspectives.  Think about this:  scaled drawings you find in the magazines do not incorporate "perspective"-they are "parallel projections" rather than the "perspective projections" produced by a camera in a photograph.  How far away is "far enough"?  Ideally, you'd like to be 10x or more as far away from the object of interest as the object is long, to keep the perspective errors in the photograph small.)

Now take the calipers and measure the height of the same doors you measured in the scale drawing.  Let's say you made a large printout of the photo, and the doors in the printout measure 1.344" tall.  You might think that we could just divide the real life door's height (74", in our example here) by 1.344" to get the scale of the photo.  But this would be inaccurate, because the photo wasn't taken from a long way away and directly side on, so the camera's "perspective projection" is distorted from the scale drawing's.  However, this photo was taken not too far below the vertical center of the locomotive, and from maybe 5x as far from the loco as the loco is tall.  So the perspective errors in the vertical dimension will be noticeable but maybe not too bad-let's give it a try:  74" / 1.344" = 55.060 scale factor in the vertical dimension of the photo.  Now measure the height of the lettering in the photo printout on the same door that you measured the height of in that photo printout.  Let's say you measured 0.172".  Now multiply 0.172" x 55.060 = 9.470".  This is your estimate of the real height of the letters on the real locomotive.

Now you need to apply some judgment.  It's unlikely that N&W used 9.470" letter height on anything.  It's more likely that they applied 9", or 9.5", or 10" letter heights using a standard set of stencils.  While your estimate is closest to 9.5", you know that the photo was taken closer to the loco than you'd like, and from a bit lower than the vertical center of the loco-so our simplified photogrammetry has some error in it.  But somebody in the N&W Historical Society probably knows what stencil sizes were available in the paint shops-or you could go to the decal manufacturers' web sites and see what scale lettering sizes they have.  If decal sheets in your scale are available in 9" scale heights, but not 9.5" heights, you could feel pretty good about using 9" lettering.  Or if they are available in 10" scale heights, but neither 9.5" or 9", you could feel pretty good about using 10" lettering.

You can use the same technique described above to figure out how far below the top of the doors you should place the top of the letters.

Once again, don't use the example results above to letter your loco!  I did not measure a scale drawing of the SD39, so my "results" won't be accurate for your work.

As far as horizontal lettering spacing goes, for most models you can just compare the location of each letter with respect to locomotive details visible in the photo you have.  But here again, it really helps to have a true side-on photo to work from, rather than a ¾ view.  So, modelers, think about the photos you are taking:  are they for artful prints to hang on your wall, or are they for helping you model a specific piece of equipment?

-Eric Bott

From: NW-Modeling-List [mailto:nw-modeling-list-bounces at nwhs.org] On Behalf Of NW Modeling List
Sent: Friday, January 02, 2015 4:39 PM
To: NW models
Subject: SD39

Guys,

In doing some research for my SD39 since I acquired the parts to build one.  I ran across this photo:

http://www.rr-fallenflags.org/nw/nw2965aga.jpg

Photo is credited to Alan Gaines taken in New Haven, IN with no date.  My question is about the road name on the long hood, can anyone provide info on this paint scheme.  This might be the unit I mode if I can find out the height of the lettering and color.

Thanks in advance,
James Wall
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