Python Solution to Dimension Tracking

The Problem

To make FreeCad work you often need to enter values of various dimensions. There does not seem to be a method internal to FreeCad ( and probably there should not be ). These dimensions come from various sources:

• Spec. sheets.
• Measurements
• Calculations
• Design decisions.

You more or less need some notes to keep track of this stuff. Some of this may be paper sketches, paper notes, and digital documents ( many may choose spreadsheets ). I find spreadsheets to be very error prone so I looked for a python solution. The very simple version of this is shown in: FreeCad Gear Box This has now evolved, and this document will describe the solution. For the actual code contact: User:Russ_hensel

A Python Solution

My Python solution consists of a set of interacting classes:

PartDimension

This class holds a single dimension. Of course you can just go: a_dimention = 22. What is wrong with that? This dimension has a name and a value. What it does not have is units or a type that may help distinguish between pure numbers ( teethe on a gear ), angles, and linear dimensions. Also I have upgraded the class so that it does easy unit conversions and is easy to print.

Here is what you might get when you print a PartDimension:

print a_dimension

output:

          bolt_sep            ( mm ) = 25.0

And here is what you get with a fairly fancy getter method:

In:
    a_dimention   = PartDimension( "part name two", dim_type = "linear", radial = False, value = 27.3, units = "in")
    print( a_dimention )

    print( a_dimention.get_value( units = "ft" ) )

Out:
          part name two       ( mm ) = 693.42
2.275

A couple of implementation details.

• Dimensions are always stored in some base units, linear in mm, angles in radians, the getter methods convert to the desired units. There are a couple of helper classes for the conversion:

• • LinearConverter
  • AngleConverter

PartInfo

Of course a part does not have a dimension it has many dimensions. So PartInfo is a collection of Part Dimensions all of which can be manipulated as a unit. There are methods to:

• Support naming of PartInfos ( say "My Gear # 3 " ).
• Add a dimension ( or a set of dimensions ).
• Access dimensions or there values one by one or as a unit.
• Print out all the part dimensions in any particular set of units.