Author Topic: DC17 Internal Precision  (Read 379 times)

Latheman

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DC17 Internal Precision
« on: December 01, 2017, 10:37:42 AM »
Ok, maybe a non-question.

The very first CAD package that I used,  Draft Choice for Windows since you ask, claimed that regardless of the displayed precision, its internal precision was something like 15 or 16 decimal digits. In other words, say you set it to calculate pi, but only display 2 decimal digits, ie 3.14, the program would actually calculate to a depth of 15 or 16 decimal digits regardless of the displayed value.

I know that DC17 can be set to display various depths of decimal digits, but have not found anything to tell me what the actual calculation depth is. Any ideas anyone?

Incidently, it's only for interest.

Regards,

Latheman

Rob S

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Re: DC17 Internal Precision
« Reply #1 on: December 01, 2017, 10:52:12 AM »
A search of the forum has reminded me of what I had long forgotten - I expounded on this precise topic once upon a time

http://forum.designcadcommunity.com/index.php?topic=255.msg1153#msg1153
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Latheman

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Re: DC17 Internal Precision
« Reply #2 on: December 01, 2017, 12:18:25 PM »
Rob,
That's the answer I was looking for.

Also, just for the record, I was well aware of the difference between accuracy and precision. And precision was what I was after.

Many thanks.

Latheman

Lar

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Re: DC17 Internal Precision
« Reply #3 on: December 01, 2017, 01:20:20 PM »

... say you set it to calculate pi, but only display 2 decimal digits, ie 3.14, the program would actually calculate to a depth of 15 or 16 decimal digits regardless of the displayed value.
You can get Pi to 15 decimal places (3.141592653589797) by entering _PI_ in most numeric fields (the snap grid dialog don't take anything but numbers and the decimal point).


Note that in the "Macros 17 review", where I got this info from, the last number is a 3, not a 7. I got the value above from dcad's "Angle and Distance" command, with the  'Distance' precision set to +15 (or the Units command without having to bother with the precision).


Lar

Dr PR

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Re: DC17 Internal Precision
« Reply #4 on: December 04, 2017, 10:27:42 AM »
V16 allows you to set the "precision" of the coordinate system to a value between -7 and +15.

I'm not sure what a "precision" of a negative number means - really imprecise?

I do recall that the actual internal coordinate system (not related to the assigned drawing units) used to work with numbers calculated to 15 digits - I think this is a double long in standard C/C++ on a 16 bit machine but I am not sure. It varies with the native data word length in the computer.

****

All we need is 256 bit integers to be able to represent the entire "known" universe with a drawing unit of the smallest unit of measurement, the Plank Length (&p = 1.6x10^-35 meter). The visible universe is about 2.8x10^59 &p across, and 2^256 = 1.15x10^77. In that case "scale" and "accuracy" are irrelevant. Everything is drawn in 1:1 scale as defined by the accuracy limit of the universe.

Of course it would be inconvenient to use 1.6x10^35 &p as the common measurement for something a meter long, so millimeters/meters/kilometers/parsecs would still be used as drawing dimensions, but would be stored internally in &p units.

I am waiting anxiously for my first 256 bit machine.

Phil
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DrollTroll

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Re: DC17 Internal Precision
« Reply #5 on: December 04, 2017, 10:51:37 AM »
Yep, DesignCAD uses double precision floating point values -- what is displayed in the coordinate bar or in dialog boxes is just the actual value rounded to the specified number of places.
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