topic Re: Area calculation in AutoCAD Forum

Area calculation

Anonymous — Sun, 18 Feb 2018 21:55:12 GMT

How accurate is the calculating area tool in AutoCAD? I have drawn an irregular shape to scale but was not sure how accurate the tool is at measuring areas.

Re: Area calculation

tramber — Sun, 18 Feb 2018 22:58:13 GMT

UNITS is a command to know to access to a certain precision level.

What LUPREC are you running ? It is reachable in the UNITS dialog.

Calculations are still very accurate taking no rule from LUPREC, but up to 16 figures behind zero.

Re: Area calculation

nrz13 — Mon, 19 Feb 2018 00:14:50 GMT

FYI, there are a few ways to measure area, but as far as I have tested, they all report the same result, which seems accurate to me.

If your object is a polyline, there's nothing extra that needs to be calculated – just click on the polyline and look at its area on the Properties palette.

If you have a hatch fill in your object boundaries, you can click on the hatch to report the area.

Then there's also the AREA command which I find I have little use for, because you trace the outline of your object the same way you would create a polyline. I usually create a polyline and put it on a non-print layer dedicated to that purpose so I can pull up the area later for quick reference.

There are probably other ways to measure it as well, but I think they would all report the same (accurate) value.

Re: Area calculation

neaton — Mon, 19 Feb 2018 17:33:24 GMT

You can also use the BOUNDARY command to create a closed polyline of an area but the command creates additional polylines. It has it's limitations but can be useful. I usually put these on a unique layer or color so they can be easily deleted or turned off. Area value is the same as all other options mentioned.

@nrz13 wrote:

FYI, there are a few ways to measure area, but as far as I have tested, they all report the same result, which seems accurate to me.

If your object is a polyline, there's nothing extra that needs to be calculated – just click on the polyline and look at its area on the Properties palette.

If you have a hatch fill in your object boundaries, you can click on the hatch to report the area.

Then there's also the AREA command which I find I have little use for, because you trace the outline of your object the same way you would create a polyline. I usually create a polyline and put it on a non-print layer dedicated to that purpose so I can pull up the area later for quick reference.

There are probably other ways to measure it as well, but I think they would all report the same (accurate) value.

Re: Area calculation

Kent1Cooper — Mon, 19 Feb 2018 18:18:30 GMT

@tramber wrote:

....

Calculations are still very accurate taking no rule from LUPREC, but up to 16 figures behind zero.

Yes, what is displayed is determined by your Units mode and precision settings, but what AutoCAD knows about it is far more accurate. But a slight correction: It's not 16 decimal places, after the decimal point [except when only a zero precedes it], but rather 16 significant figures. Compare:

Asking for a number less than one [here, 1/10 of pi, because I know it has more decimal places than AutoCAD can find] to 16 decimal places actually gets you 16 decimal places:

Command: (rtos (* pi 0.1) 2 16)
"0.3141592653589793"

But if you ask for pi, you get only 15 decimal places:

Command: (rtos pi 2 16)
"3.141592653589793"

And if you ask for [as an example] a 13-digit number plus decimal [here, pi * 10^12], though you ask to see it to 16 decimal places, you get only 3:

Command: (rtos (* pi 1e12) 2 16)
"3141592653589.794"

because 13 significant figures have already been used up before the decimal point.

In any case, 16 is the limit. You can ask for more, but it gets you no more than asking for 16:

Command: (rtos (* pi 0.1) 2 17)
"0.3141592653589793"

Re: Area calculation

tramber — Mon, 19 Feb 2018 19:42:57 GMT

I know it Kent but wanted to make it simple. I supposed too that the problem was described around less than 16 for LUPREC (you know what I mean ? it is limited to 8. half).

Everybody knows (I mean anybody who read forum for years) that some people have problems with drawings entities much too far from 0,0.

Because they use too much of those "chiffres significatifs", mainly.