Default units for expressions

[Joel_graff]

So it seems to me that if I were to enter a formula in the expression editor for a constraint, it ought to compute the result in the default length unit specified in the document preferences...

But when I type "17/32" as an expression for a length constraint, it converts to "20.92 thou" rather than 0.53 inches, even though my document units are "US Customary" and the default length unit is inches...

[GeneFC]

This has been discussed a few times recently, mostly by me.

US Customary is a completely ancient and virtually unused system of units. It is still "official" in the US, but really outdated.

The inperial decimal units system in FreeCAD works very well, but of course it is "decimal". You can enter fractions, but it will always output decimal.

I do not have any experience with the building unit system.

Gene

[papyblaise]

Try to type the formula (17/32)*1in

[openBrain]

So it seems to me that if I were to enter a formula in the expression editor for a constraint, it ought to compute the result in the default length unit specified in the document preferences...

But when I type "17/32" as an expression for a length constraint, it converts to "20.92 thou" rather than 0.53 inches, even though my document units are "US Customary" and the default length unit is inches...

Knowing you can read some code, in the short version you can find the unit change threshold in this function.

[Joel_graff]

US Customary is a completely ancient and virtually unused system of units. It is still "official" in the US, but really outdated.

The exact system I'm using is entirely irrelevant, here. My question is, when calculating a value in the expression engine, why doesn't it default to the system of units specified for the document?

[openBrain]

The exact system I'm using is entirely irrelevant, here. My question is, when calculating a value in the expression engine, why doesn't it default to the system of units specified for the document?

I just pointed out.
More specifically in your sample case :

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        else if(UnitValue < 2.54) { // smaller then 0.1 inch -> Thou (mil)
            unitString = QString::fromLatin1("thou");
            factor = 0.0254;
        }

[Joel_graff]

I just pointed out.

Right. I was trying to sort out what appears to have been a bug in my original posting... hadn't gotten around to replying to you yet.

What had me scratching my head was why it rendered 17/32" as 20.92 thou, which is 1/34.25 inches. Oddly, I can't reproduce that behavior now. Of course, it's possible I wasn't entering something correctly, but it was something that had happened several times, so I doubt it was incorrect data entry on my part. I ended up using the gnome default calculator because I just couldn't get the expression editor to do correct math, whether it was thousandths or inches.

On a side note, it would be nice to not have to fight the thousands conversion - no fun when I enter something in inches and FC insists that it should be thousandths... for some reason, unit notations aren't always easy to change.

Anyway, I'll keep an eye open for the issue I saw. I don't see it happening now.

[papyblaise]

You don't say us what config you use inches or mm
if you use inches I can't answher because I never use it
if you use mm , use mi formula it's run

[Bance]

17/32 mm = 0.020 in

[LXC]

This is just brutal. The "thou" is not helpful. If I want a cylinder that is

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5/16"

diameter, having to enter the radius takes me one step away from the dimension in its meaningful value. Then, FreeCAD converts the radius to "thou" making in meaningless. I switch my preference to Imperial to get rid of "thou". Now, when I enter, in the formula editor',

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1/2

, it shows

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Result: 0.5000

for a field that shows "in" as the unit. I hit enter, and presto, my

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.5

is now

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0.0197 in ( 1 / 2 )

. There is no "under-the-hood" explanation that makes that make sense.

Units are so fundamental to modeling that they need work correctly. Forcing users to do unit-conversion gymnastics is just not acceptable.

The hackaround is to enter:

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1in/2 

to get a half inch. Nobody thinks like that. Nobody.