topic Re: working units / Accuracy / internal storage in Modeling

working units / Accuracy / internal storage

Anonymous — Wed, 24 May 2023 06:40:38 GMT

How does archicad save coordinaties (start and end point form wall by example) to his internal database? In metric of imperial or own format? And what's the accuracy of the internal storage? How many decimals?

And what happens to the values in de database if I switch from metric to imperial?

It is possible in the metric system to draw in mm with more then one decimal? If not so: if i'm click on a random point in metric mode. Is it snappend to a invisible grid of 0,1mm? Or by example can my point floating between 145,1mm and 145,2mm?

Cheers,

Tjibbe
ARCHICAD 19 user

Re: working units / Accuracy / internal storage

Anonymous — Fri, 06 May 2016 10:08:14 GMT

Just a question, why?
in building construction it would take a very high level of craftsmanship and time (neither of which tend to be available these days) to get anything to 1mm accuracy let alone sub 1mm.
I can understand for metalwork / machining and anything being produced by computer control (mills, cutters, full scale 3D printers etc) but ArchiCAD does not control these types of devices.
Scott

Re: working units / Accuracy / internal storage

Eduardo Rolon — Fri, 06 May 2016 11:53:07 GMT

I am from the group that likes to model always to the highest precision possible. One benefit is that since AC is not rounding off then you don't get Total Dimensions that are not the sum of All Partial Dimensions. Also lets you figure out were the mistakes on modeling occurred.

Re: working units / Accuracy / internal storage

Anonymous — Fri, 06 May 2016 13:44:01 GMT

I wish I could answer the OP's original question but I don't know.

I'm pretty sure AC can move objects in smaller increments than the highest precision AC is capable of reporting. Like 1/128" of an inch or 0.0001mm type increments.

That's why I like to input values absolutely and not just eye the tracker so I get whole dimensions when ever possible.

As far as why AC should increase it's accuracy, I think AC could be used as decent CAD software outside of construction if it was more accurate or able to report is accuracy. AC is wonderful at documenting and handling projects with the teamwork function it's really being wasted on just construction.

Also, the company I work for has a 4000w industrial cutting laser (up to 3/4" steel) and I use AC to prepare files and create designs. Works great. And if I'm imputing perfect values and placing them perfectly, I can work around AC's inability to report back it's precision.

EDIT: I wanted to correct what I said here. If I have to move something that is more precise than 1/64" or 0.01mm I can't. All the drawings I have done with AC have all been logical with straight cuts, 90° corners, 1/2" chamfers, 1/4" holes and so on and so on so it hasn't mattered for us.

Granted, I'm just creating .dfx .dwg files in 2D but I understand the way AC creates 3D objects the objects are watertight by nature and makes it a good candidate for 3D work as well since AC can export .stl files (although it would be better if AC could export to .ply or AMF for this kind of work).

Re: working units / Accuracy / internal storage

Laszlo Nagy — Fri, 06 May 2016 14:53:32 GMT

I am not sure about this exact answer, but in the API it says coordinates are stored as double type C++ variables, which has a 15 digit accuracy. Someone correct me if I am wrong but I think this does not mean 15 decimal places, it means 15 digits, which may be 9 digits for the integer part, and 6 digits for the fractional part of the number (6 decimal places).
Also, what is a fact is that Dimensions can show measurements up to 0.000001 meter accuracy (if you turn on those 2 digits of extra accuracy in Project Preferences), so I guess data is stored at least to that accuracy.

Re: working units / Accuracy / internal storage

Anonymous — Sat, 07 May 2016 10:43:13 GMT

laszlonagy wrote:
double type C++ variables

I'm familiar with PostgreSQL datatypes, not C++. In PostgreSQL "double precision" is inexact floating number.

PostgreSQL wrote:
Inexact means that some values cannot be converted exactly to the internal format and are stored as approximations, so that storing and retrieving a value might show slight discrepancies.

With a float number the digits there is no reservation for the integer and fractional part of the number. The double precision type typically has a range of around 1E-307 to 1E+308 with a precision of at least 15 digits.

If AC uses floating numbers as coordinates, this means you draw more accuracy near the origin. Can somebody confirm this?

laszlonagy wrote:
Also, what is a fact is that Dimensions can show measurements up to 0.000001 meter accuracy (if you turn on those 2 digits of extra accuracy in Project Preferences), so I guess data is stored at least to that accuracy.

In my preferences the max number of digits is 4 this means: 0,0001m. And if I switch to mm it is 1 digit.

Re: working units / Accuracy / internal storage

Anonymous — Sun, 08 May 2016 03:04:47 GMT

tjibbe
I can confirm that accuracy decreases with distance from the origin, it also does this in AutoCAD and Revit, we have had an AutoCAD project where snaps stopped working because of the distance from origin
Scott