A little math help, please

[Dr. Yo]

I should be able to figure this out myself, but my brain seems to be
balking. Here's the question. I have a set of plan views, to an
unstated scale, but there is a scale bar along with the views. The
bar is listedas "50 Meters" and is 27mm long. ( The plan views are
of the 'Swordfish' class Federation ship from the Starfleet museum,
in case you were wondering ) So I can figure out that 1.85 mm =2m,
but I'm not sure how much I should reduce or enlarge the drawings to
get a set of views in 1/1000th scale...

[USS Atlantis]

Ok 1.85mm/2m = .925mm/1m or 1:1081

1000 is .925 of 1081

Invert that and you get 1081

Move the decimal and you get 108%

So scale up the print by +8% or 108% of the original

[Dr. Yo]

Thats what I needed to know-thank you, Ken!

[USS Atlantis]

So do I get first pick from the new robot line?

I need a new minion - the old one is severely out-of-date

[Dr. Yo]

Well, sure! You want that in blonde, brunette, or ambidexterous?

[macfrank]

I don't know where the "1.85mm = 2m" came from, but it's wrong.

First, get the numbers in the same units:
50m = 50 x 1000mm = 50000mm.

The scale is then: 50,000mm = 27mm long
1mm on the scale = 50,000/27 = 1852mm (or 1mm = 1.85m)

So the drawing is at 1/1852.

Since you want this at 1/1000, you have to scale the drawing up by 1852/1000 or 1.852x larger.

To double check - a 1/1000 scale drawing would have a 50mm scale bar (50,000/1000 = 50). Since the scale is 27mm long, you have to scale the drawing up by 50/27 = 1.85

For my prize, I want to decide who lives and who dies. If that's too much, I want to be able to force the inventor of MoviPrep to drink the stuff every two hours for the rest of his life (which I'm hoping will be a long one). Your choice, Doc!


Frank

[Dr. Yo]

I don't know where the "1.85mm = 2m" came from, but it's wrong.

Thats what I got when I divided the 50m scale bar by 27, its length-
I was trying to get the smallest units to see if I couldn't figure out where
to go from there....

So, by your solution I need to enlarge the drawings by 185% ?

( If so, frack. I was hoping for something under 141%, which is what
the copier at work goes up to...)

Anyway, I don't know moviprep by brand, but given our recent
conversation, I can guess exactly what its for...gimme a
couple of hours to re-align the OMCL's, and its a done deal. As a
bounus, I'll throw in an impluse to have an unwholsome attraction
to corks...

[macfrank]

So, by your solution I need to enlarge the drawings by 185% ?

( If so, frack. I was hoping for something under 141%, which is what
the copier at work goes up to...)

Yup. You can just copy it at 141%, then copy the copy at 131% (185/141 = 1.31). To double check - 27mm x 1.41 = 38mm. 38mm x 1.31 = 49.97mm - close enough for government work.

Remember that copies are not always accurate in embiggening both dimensions equally. Can you do it in a computer then print the result out?

Frank

[Stu Pidasso]

Ow. My head.

[naoto]

Remember that copies are not always accurate in embiggening both dimensions equally.

It usually depends on how the scanning is performed, though in many cases I've seen results to be noticibly wrong at the larger scales (on many copiers I've seen the scaling along the path travelled by the scanner to vary from one end to the other). You can compensate somewhat by doing two passes, flipping the master around 180 degrees. Of course this doesn't address possible inconsistency in scaling that might occur in the other dimension perpendicular to the travel of the scanner. One thing you might want to try is scaling up/down graph paper (or anything with regular marks that you can use to check the evenness of the scaling performed by the copier).

BTW, did'ya notice that 1.41 (usually the maximum size for copiers) is approximately the square root of 2 (i.e. if you scale up 141% twice, it's almost 200% ) ?

As was previously stated, perfoming the scaling using the PC will generally work better than doing it on the copier.

If you've got a faxmodem in your PC and software to receive faxes, then you've got half a scanner. All you need to do is have someone FAX the document you want to scan to you. Used that technique a few times before I'd purchased a scanner (they were expensive back in the day).

[Dr. Yo]

I expect you're both right about getting better results from
a computer than a copier, but my technological expertise doesn't
extend much past pressing buttons, I'm afraid. Still, the process
Frank described seems to have worked adequately for this set
of drawings ( a bit bigger than I would have expected, but well
within my current skills. ) Hopefully as the year goes by and I get a
more familiar with the new home system, ( a re-conned Dell running
XP pro, maybe two years old? ) I'll get a little better at this sort of
thing. Really should see about getting drivers for the printer, and new
ink cartrides too-I don't imagine the ones in there are terribly good
after seven years of idleness...

[TazMan2000]

Low cost scanners, copiers and print drivers have inherent problems with scanning 1:1. Even the most expensive ones require calibration to get perfect accuracy.

If you want accuracy without having tor resort to getting professional help, you could get free image scaling software on the net or, by trial and error.

Trial and error way;
Print out the drawing at your maximum scale of your printer driver. Scan the output and print it again until the 50 metre line gets as close as possible to 50 mm.

Image Scaling software way;
Several free ones out there too numerous to mention. Scale it at 185% and print it out. A bit of trial and error on this one as well since you have to rely on your printer driver.

Good luck,

TazMan2000

[Kylwell]

Low cost scanners, copiers and print drivers have inherent problems with scanning 1:1. Even the most expensive ones require calibration to get perfect accuracy.

Measure, measure, measure.

Even the quarter mil drum scanners aren't 100% accurate. WHen we were doing hi-resolution scans for an aero-mapping company we first scanned in a grid they made. From that grid scan they could then write an algorithm to adjust for the scanner. That had another algorithm to correct for lens issues and yet another to correct the wide angle lens distortion.

[Chacal]

The important thing to consider is that even if you can get accurate blueprints from the site's illustration (the outlines are thick enough to be more than a yard thick in scale), and build a model perfectly accurate to those blueprints, the model itself may feel kinda wonky in the flesh, because all there is of it is a set of views, with no 3D study.

That said, the accuracy of your source is low. There is no way of improving that accuracy, so relax. 1 or 2% here or there are no biggie.

[seam-filler]

Why not scan and enlarge on your computer? You won't get the fuzzy lines you get each generation a photocopy gets.

[LindaSmile]

I need help with my math too.

[Dr. Yo]

Heheh. Good to know that 911 operators can have a sense of humor
and proportion....


Chacal- Yes, its never appeared on any kind of screen other than
a computer, so there's not a lot to argue about. I will be looking
back at the SF Museum site to see if there are any 'artists interpretations',
which I know exist for some ships.

I respect those who desire as close to perfect a replication of their
source as possible: I simply have no desire to emulate them.

[naoto]

Let's think about this for a moment...
Since your target scale is 1/1000 that makes things easy. This scales out to 1 metre on "real" article being represened as 1mm on the model. This means that the 50m bar should be printed so that it comes out to 50mm (5cm) in size.

If I save the image from the website (see below for locating image) and then load it into MS-Paint, I see that it is 868 x 451 pixels at 72dpi (select Image / Attrributes... ). At 72dpi, the image would come out as 12.05" x 6.26" (or 30.62cm x 15.91cm). The 50m bar is 107~108 pixels wide (one end isn't solid black but grey, so I would interpret the bar to be slightly longer than 107 pixels but less than 108 pixels -- we'll use 107.5 for convenience).

If we take the longest dimension of the picture, we see that it is around 8.07 times the size of the "50m" bar -- which would scale out to 403.7m. So basically we want to scale the image so that it is 403.7mm, or 40.37cm. If we divide 40.37 by 30.62 we get 1.3184, which is the scaling factor we're after.

So... getting back to the image loaded into MS-paint we just go to File / Page Setup... then set scaling to 132%. If I set the margins to mimial values, I can get the image to print on 2 sheets of paper on the printer I've got. After printing the image, I measured the 50m bar -- sure enough, it's 5cm!


BTW, it actually took a bit longer for me to locate the image you were referring to than to actually do the above. To locate the image:
1. Go to http://www.starfleet-museum.org/
2. Under the 22nd centry section and click on the Paris Class link.
3. About 3/4 down the page, locate the link to SWORDFISH class ( http://www.starfleet-museum.org/alburak.htm )
4. On this page you'll find link to JPG file

[Umi_Ryuzuki]

Let's Simplify this whole thing...


I want to build X ship.
At 1/1000 scale, the X ship builds out to 11 inches long...

When I print out the drawing I found,
it measures 3.375" long....
What percentage should the drawing be
copied at to make it 1/1000 scale?

11 Inches is the ship at 1/1000, so

11 ÷ 3.375 = 3.25

Therefore to enlarge the 3.375" drawing to 11", we
copy the drawing at 325%...

Seems simple enough to me...

[macfrank]

So... getting back to the image loaded into MS-paint we just go to File / Page Setup... then set scaling to 132%. If I set the margins to mimial values, I can get the image to print on 2 sheets of paper on the printer I've got. After printing the image, I measured the 50m bar -- sure enough, it's 5cm!

Yeah, but that's on your printer. You're confusing the situation since Dr. Yo has already printed a copy with whatever printing device that he has available, and it produced a 27mm scale bar. You have to work with the data that you're given.

[Dr. Yo]

Because my memory isn't what it used to be, I'm printing out the
whole magillashlinginangin* thread-never hurts to have hard copy.

I appreciate everybodies advice and insight-I only wish my builds got as many comments





* Woldercanese-it doesn't translate.

[naoto]

So... getting back to the image loaded into MS-paint we just go to File / Page Setup... then set scaling to 132%. If I set the margins to mimial values, I can get the image to print on 2 sheets of paper on the printer I've got. After printing the image, I measured the 50m bar -- sure enough, it's 5cm!

Yeah, but that's on your printer. You're confusing the situation since Dr. Yo has already printed a copy with whatever printing device that he has available, and it produced a 27mm scale bar. You have to work with the data that you're given.

As I understand it, the picture was obtained on-line, so if we're going to rescale it using the computer, we might as well start from the original image. MS-Paint (at least the one in Windows XP) uses the DPI tags stored in the image file to scale printouts -- so it should scale out the same regardless of the printer (as long as you don't use the "fit to paper" options). BTW, I've noticed that neither word processors nor web browsers seem to honor the DPI information in image files consistently when scaling images for printout -- resulting in different results on different printers, and in some cases slightly different results from different computers but with the same printer.

One note regarding downloading of images from websites -- you get different results from right-clicking on the image on the webpage and performing "Save As" and performing a Copy then Paste into a graphics program. The "Save As" from the web browser will download image and preserve tag tag information like DPI, whereas copying to clipboard often doesn't.

As stated earlier, there are problems with scaling on many photocopiers, as the scaling is often uneven, so that'll complicate matters somewhat. The other problem is that what was originally one sheet of paper becomes at least two -- now you have to worry about alignment of the different sheets of paper. You'll need to add some sort of alignment marks on the original so that you can line up the different parts. I've done this sort of thing before -- using the scaling of a photocopier to scale up/down drawings, and learned that it's generally not as simple as it seems (it gets complicated if you have to run through multple passes -- distortions get magnfiied with each pass).

[Umi_Ryuzuki]

It's simple algebra,

Use my example, and plug in your own numbers...

[naoto]

It's simple algebra,

Use my example, and plug in your own numbers...

Strictly speaking it's really only arithmetic (granted application of basic algebraic concepts to aritmetic).

To repeat what I've said earlier -- it's easier to scale up/down on the computer with graphics software (can even do it from MS Paint in XP) than on the photocopier.
1. Computer yields much wider choices of scale factors. Most photocopiers can't go above 141% -- so you need several passes.
2. Most graphics programs will automatically chop up picture to print on separate pieces of paper. Photocopiers I've tried used for scaling up/down images tended to simply clip the image at the edges -- so you need to manually relocate the original so you get the complete image. Alignment becomes problem.
3. Usually the scaling factors are more consistent than on photocopier. Most photocopiers I've tried seem to be uneven on the scaling. In some cases the scaling varied along the length of the paper (i.e. looked like the "keystone" distortion you might get with a projector image). This especially becomes problematic if you have to run through multiple passes.

*** One very important point --- Do not use the "fit to page" option. Any computations you make for scale up/down factor will be completely meaningless if you do.

Do mermaids wear algae bras?

[rokket2001]

Umi is right - it's dead simple math. Scale math is always:

ORIGINAL into TARGET.

end of story. dead simple. Works for Up or Down.

To make something that is 5mm long (ORIGINAL) = something that will be 8mm long (TARGET):

8 / 5 = 1.6 ...or enlarge 160%.

MANY copiers enlarge up to 200 or 400%. Copiers even 5-8 yrs old.

As mentioned by others, a graphics program (preferably a drawing/vector program) will certainly help you get to almost any point between percentages. If you need to enlarge something a percentage point PLUS, copiers aren't too good. But you could scale up or manual tweak an image in a graphics program, then just go to a good copy shop and PRINT it out to a printer at 1:1, at that point it will be "perfect".

[rocketrider]

* grabs popcorn and sits back *

This is like a math soap opera