Converting Decimal scale factor in viewports

[eddlewington]

Please forgive me because I'm absolutely shocking at maths and google hasn't really helped.

When using the mouse jog wheel to control the viewport scale factor in autocad it gives you a decimal scale which seems to be quite handy for getting everything to fit inside a view port on a given paper size. For example 0.007369. How do I convert this to a 1:XYZ factor (eg - 1:1250). I've always struggled to get the scale factor right in viewport. Usually I go through a view options until it's close enough but it will usually end up with me adding at least 3 or 4 custom scales.

I'm sure there is some equation to convert the decimal and then round to the nearest factor but I don't really understand the maths or how to work this out. Can anyone spell it out for someone who's mathematically challenged? Or is there a better way of getting the scale factor right? I'm usually drawing 1:1 metric in model space for event maps etc so tend to need a big scale factor in paperspace. I could be working on an area that is easily 1000m 'real world'.

Hopefully this makes sense, any help would be greatfull received!

[RobDraw]

You don't need a mathematical conversion to do this. You can use the properties panel or the view scale at the bottom to select from a list of predefined standard scales.

[eddlewington]

Thanks but I'm not sure you understand me correctly. My point it that the predefined view scale rarely works for me so it's trial and error adding 1:50, 1:650 and so on. The jog wheel allows scaling up and down beyond the standard 'default' scales. It's this conversion that I want to work out.

[ChicagoLooper]

If you are using the ‘jog wheel’ to make your linework fit within your viewport, then you are forcing your printed drawing to use a nonstandard scale. By nonstandard I mean a scale that doesn’t use round numbers in their ratio.

For example 1:47, 1:353 or 1:1752.43 are all nonstandard scales. Although changing those scales to 1:50, 1:350 or 1:2000, respectively (they have nice round numbers), will adjust your zoom factor, they’re more common, easier to understand and will reduce confusion in your audience. Nonstandard scaled drawings are typically labeled NTS or not to scale. 

Your mention of decimals is a valid one. To make things easier avoid relying on those decimals and use the scale dropdown list in the Taskbar instead. (The dropdown list is near your clock). If the dropdown list is inadequate, you may customize the list by adding more scales. If you add, however, make sure you add one with nice round numbers that end in zero, the more zeros the better. 

Assuming you use real world millimeter units while drawing in modelspace, the viewport ratio 1:1000 means 1mm measured on your printed hardcopy = 1000mm in the real world. Notice the RATIO is ‘defined’ as mm to mm, NOT mm to meter. Technically speaking, all viewport ratios are unitless and that means a viewport ‘definition’ is always mm to mm in a metric drawing (or inches to inches in imperial).

[Valentin_CAD]

@eddlewington ,

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@eddlewington wrote:

...  convert the decimal and then round to the nearest factor...  Or is there a better way of getting the scale factor right? 

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In addition, you may want to check the "Percentages" to help you select the closest standard scale to your decimal.

Example: 

The current viewport has a decimal scale of .312778. The closest scale option is 1:4 / 25%,  (you can add /customize more). I suggest you customize your scale list to facilitate your future selections. 

[dany_rochefort]

Like Robdraw says, you don't need a mathematical approach to do this.  

Here is a my solution for setting up perfect viewports at any scale, posted to the forum in january. The example shown is for scale 1:1. However, it works for all scales, you just need to scale the red rectangle to whatever scale is needed and apply the procedure as shown. 

https://forums.autodesk.com/t5/autocad-forum/need-a-crash-course-in-paper-space-and-viewports/m-p/10...

[skintsubby]

Hi @eddlewington

Have you tried just typing it in on the CUSTOM SCALE part on the properties palette?
ie.. Select the viewport, then in the CUSTOM SCALE area type in 1/250 (or whatever other scale you want). It then automatically converts it to a decimal.

Mark

[Pointdump]

Hi @eddlewington,
"...it's trial and error adding 1:50, 1:650 and so on."
That's how everyone does it, me included.
For the math part, 1:50 is 1/50, 1:650 is 1/650, etc.
If the scale shows 0.007369, that's 1/0.007369, so ≈1:136.
That's my take on it. Does that look right?
Dave

[dave_barrXKWBX]

Type the exact decimal scale you have after scaling with the mouse into a calculator and then hit the 1/x key which will give you the actual scale in a 1:xxx format.  In your example above, 0.007369 equates to 1:135.7036923287 which is a bit non standard  You could use 1:135 or round it to 1:125 or maybe 1:150 which would be a little more standard.  Hope this helps

[AllenJessup]

I've rarely worked in metric and then in standard scales. The way we used to do it in imperial would be to do a Zoom Center in the VP at 1/(Scale)XP. So a 20 scale would be (1/20) 0.05XP. You can type the formula 1/20XP for the magnification height and it will work.