Feature request: Reduced Units.

[jruiz]

I think it could be very useful that FC have the option for the users to impose their own "reduced units".
That is, once user select the unit system of his/her preference (Standard, MKS, ...). Instead of using (for example) mm as length unit, use the length of some selected edge. This length would be the "length reduced unit" (LRU). Then each other distance involved in the project would be a respective factor times this LRU.
This way, the LRU would give the "size of the project" while the set of factors would give its form, of course form will be subject to structure of the design.

[openBrain]

Even if I think there are much important things to fix in FreeCAD, I'd say "why not?". However I'd see something more simple : just a virtual unit (let's call it "uu" as User Unit) that will be a property attached to the document and as such can be set by user to a defined length and used in model.

[jruiz]

Even if I think there are much important things to fix in FreeCAD, I'd say "why not?". However I'd see something more simple : just a virtual unit (let's call it "uu" as User Unit) that will be a property attached to the document and as such can be set by user to a defined length and used in model.

...That's the main idea. Each project/document would have its own (set of) unit(s).
It is a common practice to use reduced units in (for example) computational physics. I think this scheme could be adopted here.

[jruiz]

Even if I think there are much important things to fix in FreeCAD, I'd say "why not?". However I'd see something more simple : just a virtual unit (let's call it "uu" as User Unit) that will be a property attached to the document and as such can be set by user to a defined length and used in model.

@openBrain Have you read the post Feature Request: Extend equality restriction in the sketcher.
If so, could you give me your impressions about it?

BTW, It is related to this post, and if it would be implemented, the implementation of Reduced Units would be straightforward.

[kisolre]

Or it could be just a visual representation as in all unit systems? Allow for existence if user defined local (for users installation) unit systems - basic units defined with names and ratio to SI units and prefix units, defined as ration to basic units. "1 Brunk" = 3.764 mm; "1 fiBrunk"= 40.65 Brunk. Allow input and display only as decimal notation - no 2 fiBrunk 3Brunk, keep that only for preexisting unit systems. Internally everything stays in SI as ois now.

[chrisb]

Or it could be just a visual representation as in all unit systems?

As much as I would like to have a global scale possibility, I think this is what could be implemented as a user made unit.

[jruiz]

...I think this is what could be implemented as a user made unit.

...well it was what I was thinking about when wrote this post...
The "proportionality" restriction has a "side effect" of helping in using (the non implemented) reduced units on sketches.

[MSOlsen65]

Hello everyone,

What @jruiz is speaking about what is sometimes referred to as "Relative Measure" (RM) or Unit Measure. In RM, one chooses some aspect of a sketch or part. The length of that aspect is set as the "Unit Length" (i.e. a length of 1). Then all other lengths are expressed as their proportionality to the Unit Length. In Joinery, we call this using "Relative Measure" because everything is related to a single part. It is a handy way of reducing the complexity of numbers in design and building.

Later, if the design needs to be set to a specific measuring standard, it is a simple matter to apply that standard directly. If it has to be scaled, everything is simply multiplied by the scaling factor. This is commonly done in mathematics when talking about trigonometry and conic sections where everything is related to a "unit circle" (i.e. a circle with radius = 1). It is in essence a "unit-less" way of working. While it does not work for everything, when used properly, it is a great way to reduce complexity without loss of information.

For example, my Corner Display Cabinet, is a pseudo-example. All, or nearly all, of my "numbers" are relativistic relationships between material specifications, and design constraints ("Corner Unit Dimension" in my spreadsheet) using the expression engine and spreadsheet. If it were a true RM, I would have:

1. chosen a single spreadsheet entry
2. set that entry equal to 1
3. set all expression engine entries to multiples of 1

After my design was complete, I could simply assign a measurement system and scale my RM by the appropriate factor. In this case I could easily have chosen the thickness of my plywood as my RM, because that dictated most of my other consideration. Thus 0.75 inches is divided by itself to get the RM of 1, and as a result, the measurement indicators (inches) cancel out: 0.75 inches = 1.

RM would definitely have simplified many of the expression engine entries, and made data entry both faster and less error prone. It would also make the design simplistically scalable and convertible to any length measurement system (simply measure the thickness of the plywood in the chosen system and multiply everything by that value adding the system notation -- in, ft, mm, km, etc.). For an automated factory, the simplified scheme with its ease of scale makes robots and other CNC machines simpler, faster, and more accurate to program and operate. The hard part is getting people to look past the units and numbers. Once that is done, RM becomes an amazing powerful tool.

The drawn back of RM can be the hiding of how relationships were determined. In my example, some relationships where a combination of design constraints and multiple materials constraints as shown by some of the complex expression engine statements. For myself as a Joiner, these relationships are at the heart of Joinery, so loosing them for a simplified numbering scheme would be a difficult change for myself lat least. Hence my choice of a pseudo-RM.

Link to my Corner Display Case FCStd file: https://www.dropbox.com/sh/ireycs387arn ... lRkAa?dl=0

[jruiz]

Wow @MSOlsen65 what an explanation! Congrats.

While it does not work for everything...

Are you sure? hahaha.

...Thus 0.75 inches is divided by itself to get the RM of 1, and as a result, the measurement indicators (inches) cancel out: 0.75 inches = 1.

How about saying that 1RM = 0,75 inches?

The hard part is getting people to look past the units and numbers. Once that is done, RM becomes an amazing powerful tool.

I agree completely.
So people are invited to take a look a this way of working. For sure you'll like it!

The drawn back of RM can be the hiding of how relationships were determined...
...For myself as a Joiner, these relationships are at the heart of Joinery,

so loosing them for a simplified numbering scheme would be a difficult change for myself lat least.

I like very much using the spreadsheet for storing parameters and using alias for referring cells. Normally I group them into dependent parameters and independent parameters.

I think that all these parameters and the relationships you talk about between them could/should be stored in a spreadsheet.

[Kunda1]

Hello everyone,

Fantastic explanation. Perhaps at some point you'd be interested in helping us with documentation of FreeCAD on https://wiki.freecadweb.org ?