topic Re: Dimensions in AutoCAD Forum

Dimensions

Anonymous — Wed, 21 Feb 2018 12:48:59 GMT

Does anyone know how i can draw shapes of specific dimensions and have the Linear Dimension function give me the exact same measurement....I will explain, I am making rectangles, squares and curves using Draw function...horizontal with exact measure I type in (eg 2.375), then right angle, type in 6.750, enter, and repeat to finish the rectangle. The dimensions are fixed but when I check later using Linear Dimension the values are different by fractions...eg 2.435 instead of 2.375 and others less eg 6.697 instead of 6.75. This becomes a problem when some measurements are taken from a previous shape. Many of these squares and rectangles are overlying, so is it possible that I am picking up a different reference line? I try to use Endpoint or Intersection point at all times. I do notice several lines instead of one single reference line when I enlarge to high resolution. I tried using the exact measure on Linear Dimension first then adding the design lines in a different colour but the Dimension line always comes up with a Yellow sign with an Exclamation point...obviously it does not like that method.

I am using "feet" for measure and decimal fractions for inches...my foot is different in length because of historical reference but that should not matter until I change to scale the model down to metric and then can be adjusted.

Thanks. John Davis

Re: Dimensions

TheCADnoob — Wed, 21 Feb 2018 13:43:42 GMT

It sound like there may be some unwanted snapping. Possible snapping to the wrong point when you run a measurement.

I might try a couple things. I might try turning off all snaps (OSNAP and SNAPMODE) and use the Cntrl+Right click (also Shift+right click can do it) to enable only the snaps you want to use momentarily.

Another approach would be to temporary explode the rectangle and look at the properties for the line to see if the length you are measuring is actually the length of the object.

The exclamation point just means you 'detached' the associated object you are annotating. Its a visual to let you know that the dimension is no longer really measuring the object.

Re: Dimensions

pendean — Wed, 21 Feb 2018 13:46:06 GMT

Post your DWG file, show us your work: thanks.

Re: Dimensions

Anonymous — Fri, 23 Feb 2018 13:45:48 GMT

This reply is for pendean (consultant)........to give you a little
background....I started Autocad in Jan this year and am using a book
Autocad 2018 for Beginners from CADFolks. Up to now I have not needed to
get into 3D. I am using "feet" as my measurement, although my "foot" is
actually different- One Venetian foot =347.73 mm = 13.69 Imperial inches.
I use decimals because Venetians used 12 inches (or fingers) to the foot
where 1/8, 1/4, 1/2 feet were required and 12 to the foot where 1/6, 1/3
, 2/3 were required.....they did not used decimals at that point in the
13-1500s...at any rate the only problem for me will be to calculate the
conversion to metric when I scale the drawings for construction....I will
leave that to my mathematics friend.
In the example I have sent you will see lots of yellow marks...more than
the other drawings I have made, but you will probably see multiple lines
in the axis lines. I use second or third measurements often taken from
the first measurement (the texts are written this way) so instead of using
a ruler and marking a point to start a new vertical or horizontal I must
make another multishape which eventually creates multiple lines on the
starting axis lines...which leads to faulty measurements in Dimension
mode. I still have not found out if it is possible to measure points out
along an axis, mark them, remove the second line and measure up from the
marks to another height or a two phase line to create another rectangle
instead of 4 lines for every rectangle.
The second example took me quite a lot of time using exact measures for
each side of a square or rectangle...to find that the measures taken at the
end did not match....sometimes out by hundredths or thousandths of an
inch. How accurate is this program and can that be adjusted? and where?
This works is involving me in an archaeological project and my mentor has
already shown me what even 1-2 mm difference in a measurement can make.
In any reply please keep in mind that I am not long experienced in this
program.
Thanks in advance,
John Davis, Venezia.

Re: Dimensions

pendean — Fri, 23 Feb 2018 13:56:04 GMT

No file attached my friend; you will need to come to the website to post files and images.

Re: Dimensions

Kent1Cooper — Fri, 23 Feb 2018 14:22:58 GMT

@Anonymous wrote:
.... How accurate is this program and can that be adjusted? ....

It's far more accurate than shows in display. It keeps values down to 16 significant figures. You can set to what level of precision you want displayed values to show, in the UNITS command and in Dimension Style settings, but that doesn't affect the accuracy of the underlying data.

I agree that it sounds a lot like Object-Snap is affecting where things end up.

I'm fascinated by the Venetian-feet concept. Here in the Philadelphia area we need to deal with a similar, though simpler, quirk. It's something along the lines that the city was originally laid out using a surveyor's chain that was too long by 1/4 of 1%. So under "Philadelphia District Standard" [PDS] measure, what is called 100' is actually 100'-3" in actual measure. Since all original records of block sizes, street widths, etc., were under PDS, the City requires that all surveys and Civil Engineering use it, and all submissions for permitting, etc. We Architects have to be aware of it so that buildings site properly on sites, and we know how much space there "really" is, and fortunately there's always a little more room than the PDS measurements suggest. I had a project on a block 400' long in PDS, which was very convenient because it meant the actual block length was a nice clean 401'.

Re: Dimensions

Anonymous — Fri, 23 Feb 2018 15:27:48 GMT

To pendean..........files do not attach here? where in the site should I
go?

Re: Dimensions

Kent1Cooper — Fri, 23 Feb 2018 16:57:10 GMT

@Anonymous wrote:
....files do not attach here? where in the site should I go?

They do attach here, but [at least for some people under some circumstances -- I don't know whether it's device-dependent or something] you can't attach files when Replying to a Post via a cell phone, but must get into the site on a "real" computer to do it.

Re: Dimensions

Anonymous — Fri, 23 Feb 2018 17:17:48 GMT

I am on a real computer, I do not use my cell phone as a computer.

Re: Dimensions

pendean — Fri, 23 Feb 2018 17:32:59 GMT

you have to come to the forum in a web browser to post files and images.

Re: Dimensions

john.uhden — Mon, 11 Mar 2019 16:13:03 GMT

That reminds me of the programming assignment I got for Philadelphia Gas Works. I had to perform 23 separate operations on over 13,000 dwgs to make them approximately fit some kind of standard (perhaps it was for GIS). I don't remember each of the 23 operations. John Cooke spelled it all out for me, but one of them was scaling. Whatever... it all worked just fine, no errors, and the client was thrilled.