Making Scale Drawings by Jon Monon

Discussion in 'The Academy' started by shamus, Aug 22, 2003.

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  1. shamus

    shamus Registered Member

    In this "how-to", I will attempt to illustrate how to make a scale drawing
    from simple photographs taken of a building. For this example, we'll use my
    grandfather's blacksmith shop in Turin, Iowa. The goal is to get the drawing,
    and thus the model, as close to scale as reasonably possible. The smaller
    images may be clicked to enlarge.

    The first task, as with many prototype projects, was research, in this case,
    gathering photos and a little information about the building. Ideally, it
    would be nice to get a photo taken from the front,back, and both sides,
    showing the whole building. It's also nice to have close-ups of any special
    details and an indication of height somewhere in the picture, like you or a
    relative. You will probably not have this luxury, unless you are the
    photographer. If you are there taking the pictures, you might as well get
    some measurements if you can get that close to it. With the Turin Blacksmith
    Shop, at least until someone can get there and get some better photos, we
    only have a good front view, a partial side view, and a front view with
    people for height reference.


    I also have a little history, as well as modeling ideas from an earlier image
    in this newspaper article. The lower photo is the shop, and Jens Paulsen,
    mentioned in the article, is my grandfather, who passed away at a young age,
    before my own birth. I have some more information on Turin and the blacksmith
    shop maintained on this
    separate page.

    to view a larger copy of this image.

    Armed with this information (thanks Mom!), the next step is to extract the
    information in the form of measurements. I printed the scanned photos and
    used dial calipers to take the measurements. You could use a plain scale (a
    ruler) as well, and it should prove accurate enough for our purposes. I like
    the calipers because they can be used to transfer the measurement to paper,
    and the decimal divisions are easy to work with. The measurements can be
    transferred to a crude hand drawing. Graph paper works well for those who are
    challenged in this area, like myself. The drawing is made as the measurements
    are taken, so it comes out 1:1 from the photo. It doesn't matter what it
    looks like, as this is an interim step. You may wish to save it for
    reference, but it will not be the final drawing. I used the best photo
    (above, center) for all the measurements of the front. Measure as accurately
    as possible, but there will be some rounding in the end. There are also
    distortions in the photographs that you will have to "fudge." In this case,
    all vertical measurements were taken from the top, and horizontal
    measurements from the left side. I use the top as reference because the
    ground is uneven and the left because it's taller. Measure all the dimensions
    of the building itself, and all the details you want to model, such as door,
    windows, chimneys, roof lines, gutters, etc. Make a mental note and measure
    anomalies, such as the left door in these pictures, which is wider than the

    The next step is probably the hard part for those who feel grumpy about math.
    We need to determine what scale the drawing we just made is, so we can label
    all the measurements in what we believe them to be in actual 1:1 feet. It's
    not likely our drawing will come out to exact HO scale! That's why I do an
    interim drawing (it also gives us a nice place to scribble without messing up
    the finished product). We have to take a measurement of a known commodity in
    one of the photos, in this case, my father. Bet he didn't know he was a
    commodity! He's about 5 ft 9 inches. We gotta do sumpthin' 'bout that. That's
    just too hard to work with, but easy to convert. 9 inches, just happens to be
    3/4 foot, which is .75 ft, so 5 ft 9 in = 5.75 ft. That's better. Next I
    measure him in the photo, and part of the structure behind him, in this case
    the door height. He measures 1.25 in and the door 1.75 in. So we use the


    Known item is the item in the photo that we know the real height of
    (my father)
    Unknown item is the item in the photo that we don't know the real
    height of (The doors)

    By use of cross multiplication and division, we find the height of the door
    is 8.05 feet. We probably have a little distortion or measurement error in
    the picture, so we will just call it 8 Ft.

    To simplify the math, you can just multiply the unknown item (as measured in
    inches from the photo) by the known item (as measured in feet in the real
    world). Then divide the answer by the known item (as measured in inches from
    the photo). The answer will be in feet. Example: 1.75 X 5.75 = 10.0625.
    10.0625/1.25 = 8.05 Feet.

    Now that we know the door is 8 feet tall, and on the rough drawing (and the
    photo we are taking measurements from) it is 1.6", we can surmise 1.6" = 8
    feet. If we divide both sides of the equation by 8, we get a more manageable
    .2" = 1 foot, or you can divide both sides by 1.6, and you will find 1 inch =
    5 feet. Because you are allowed to do an operation to one side of the
    equation, as long as you do the same to the other, both are true:


    Had the photo with my father and his handsome sons not been on hand, the math
    would have been simpler, but based on an assumption and therefore less
    accurate. I could have guessed the door at 8 feet or a window size. With the
    door, I would have been off a bit by assuming the inside was 8 feet, not the
    whole door to include trim. I would have gone straight on to surmise the
    measured height of the door opening of 1.540 = 8ft. So .1925 inches would
    equal 1 foot, or 1 inch = 5.195 feet. Probably not a big error by the time we
    round things off.

    So, now that we know .2 inches = 1 foot, we can convert the measurements from
    the photo to feet. This can be done by dividing actual measurements taken
    from the photo by .2 or if you are using 1" graph paper as I did, you will
    notice that 1 minor division is .5 feet, 2 minor divisions is 1 foot, etc.,
    so you can just eyeball it. Note that as you divide by .2, the number gets
    larger. Example: I measured the building height at 3.140 inches. 3.140 X .2 =
    15.7 feet.

    The Final step is to redraw it "in scale" or, at least, make a drawing that
    shows what size the model will be in scale. For this final step, you can use
    plain paper, graph paper or computer software. I chose to use a Linux program
    called Xfig. I chose Xfig, because it's an
    easy to use, powerful CAD program, and it has a nice benefit of exporting to
    pdf, which prints at the correct size without meddling with it. In my
    opinion, if you don't have access to a decent CAD program, graph paper is the
    next best choice. If you use plain paper, it would be advisable to use a
    protractor or a square to ensure the 90 degree corners are reasonably square.

    Once you decide how to do the final drawing, it's simply a matter of using
    your scale ruler to draw out the lines to the right size in your scale or, if
    you are using a computer, you just have to divide by the conversion factor
    for your scale (that's just the ratio 1:whatever). For O scale, divide actual
    feet by 48, HO divide by 87, and N divide by 160. You can find more scales at
    the NMRA website.


    Since the intended result is a drawing that will be the same size as the
    structure you are building, it is not necessary to label each dimension. It
    may be a good idea to label a few of them and/or place a 1" line and indicate
    how many prototypical feet it equals. This is important to do if you are
    working on a computer, so you can verify the size has printed correctly.

    If you are interested in building this blacksmith shop, I will place the
    drawings for the other sides, as well as any updates
    There is already a
    recent photo.
    You can download/view/print the pdf version of the above

    Special thanks to Dick (absnut) and
    Shamus for
    editing, inspiration and encouragement, as well as to my parents for
    providing childhood memories of Iowa, the photo images and the documentation.

    The latest beta version of this ongoing project may be viewed at
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