convert units?

adamohern

Silly question. I have a length parameter expressed internally as meters. I would like to know the same value in inches. How can I get the length map's value converted to inches?

cody_armstrong

@adamohern  You should just be able to multiply it by "inch".  

var inchUnits = value * inch;

adamohern

As in:

var inches = definition.myLength.value * inch;

That doesn't give me the proper value, nor would I expect it to.

adamohern

If it helps to clarify my meaning, here's what I'm currently using as a workaround:

// To use formula, we need to start with Inches (not meters)
var mercury_planet_dia_inches = definition.mercury_planet_dia.value * 39.37007874;

ilya_baran

You divide by inches, not multiply by them.  Dividing a length by a length gives a number.

var inches is number = definition.myLength / inch;

cody_armstrong

Ah I misunderstood, what about just multiplying everything by a conversion factor? 

var inchConvert = 39.3701<br>var inches = value * inchConvert

adamohern

Ilya nailed it, as usual. I find the unit conversions in FS confusing. (I'm sure they make sense to a math person.)

kevin_o_toole_1

@adamohern There's definitely a bit of a zen to units in FS: One should think of a length as "just a length" and not really having units. If I have a length variable (of type ValueWithUnits), it does not matter whether that variable was originally entered by some user in inches, or created in FS via  * centimeter, or gotten from evDistance, or calculated by dividing "just a volume" by "just an area". All these are just lengths. I can take one length, subtract another length from it, pass the result into a function that expects a length, all without caring about units.

The flip side of this is: if you find yourself wanting to create a variable like "numberOfInches", it's worth thinking about why. That variable does have a bias about its own units, and once you create it, those units will need to be considered for the whole lifetime of that variable. numberOfInches can't be added to other FeatureScript lengths, nor can it be passed into functions expecting FeatureScript length. So, you're going to be paying the cost of maintaining such a variable every time it interacts with something else in FS.

You can instead write code which takes advantage of FS units in formulas, like:

const mercury_planet_density = 5.43 * gram / (centimeter^3);

const mercury_planet_radius = definition.diameter / 2;

const mercury_planet_volume = (4 / 3) * PI * mercury_planet_radius ^ 3;

const mercury_planet_mass = mercury_planet_volume * mercury_planet_density;

The result, mercury_planet_mass, is "just a mass". By default, a ValueWithUnits will print in SI units (in this case, "3.3031834839597105e+23 kilogram"). You can see that value with different units by dividing out the units before printing, like println("Mass: " ~ mercury_planet_mass / pound ~ " pounds");

adamohern

Thanks, Kevin. I understand the principle, and as a rule I do exactly what you describe. I had two problems that were forcing me (as far as I could tell) to use an inch-specific number: 1) I inherited a formula from an engineer that for some reason only worked with inches, and 2) I was having trouble raising distances to decimal powers (root). Not sure why #2, but I found that working with real numbers (as opposed to distances) fixed the problem.

patrick_farley

i have almost the same issues and dividing by / inch does not seams to work?
Here is a snipet of my code:


This works but give me a some decimal at the end

 //var inches = definition.myLength.value / inch;

        if (definition.size == Size.X204)

            {

            var sketch01 = newSketch(context, id + "sketch01", { "sketchPlane" : qCreatedBy(makeId("Top"), EntityType.FACE) });

            skRectangle(sketch01, "rectangle01", { "firstCorner" : vector(0, 0)* inch,"secondCorner" : vector(3.5, 1.5) * inch} );

            skSolve(sketch01);

            extrude(context, id + "extrude01", { "entities" : qSketchRegion(id + "sketch01"), "endBound" : BoundingType.BLIND, "depth" : definition.myLength });

            //setProperty (context is Context, definition is map)

             setProperty(context, {

                    "entities" : qCreatedBy(id + "extrude01", EntityType.BODY),

                    "propertyType" : PropertyType.PART_NUMBER,

                    "value" : ("2\" x 4\" x "~(definition.myLength.value * 39.37007875))

            });

            



but if i divide by inch
i get :

        if (definition.size == Size.X204)

            {

            var sketch01 = newSketch(context, id + "sketch01", { "sketchPlane" : qCreatedBy(makeId("Top"), EntityType.FACE) });

            skRectangle(sketch01, "rectangle01", { "firstCorner" : vector(0, 0)* inch,"secondCorner" : vector(3.5, 1.5) * inch} );

            skSolve(sketch01);

            extrude(context, id + "extrude01", { "entities" : qSketchRegion(id + "sketch01"), "endBound" : BoundingType.BLIND, "depth" : definition.myLength });

            //setProperty (context is Context, definition is map)

             setProperty(context, {

                    "entities" : qCreatedBy(id + "extrude01", EntityType.BODY),

                    "propertyType" : PropertyType.PART_NUMBER,

                    "value" : ("2\" x 4\" x "~(definition.myLength.value / inch))

            });

i did enter the lenght in INCH at the interface,



Any idea?
Thanks

Pat Farley

NeilCooke

Try it with just "value" : ("2\" x 4\" x "~(definition.myLength / inch))

You were dividing a number by a "ValueWithUnits"

patrick_farley

Thanks,
now i have inches but the other issues is , it is not rounded to the value i enter (32 inches)

i don't think that i could ask the builder to cut a 2x4 at 31.9999 inch ;-)

i will problably have to round it to the nearest 1/16.
i did not search for this function yet, is there anything that could do the job?

Thanks for your help guys

Pat Farley

patrick_farley

Thanks i just found the round() function
i am trying this
i will let you know my find

Pat F

patrick_farley

Perfect
it now works with round(

             setProperty(context, {

                    "entities" : qCreatedBy(id + "extrude01", EntityType.BODY),

                    "propertyType" : PropertyType.PART_NUMBER,

                    "value" : ("2\" x 4\" x "~(round(definition.myLength / inch, 0.0625))~"\"")

 
Pat Farley

NeilCooke

Glad you got it sorted

kevin_o_toole_1

FYI to future users, the round function also takes a precision, if desired. You can use the function either with units: round(length, millimeter) or without: round(number, 0.01), depending on what units the original value has.

There's a few examples of printing values with units in a sane way at the top of the units module.

MichaelPascoe

The feature I'm working on will be used in both metric and english part studios.

@kevin_o_toole_1
This may have already been answered and I missed it.
Is there a way to query the units that are on a number? Or perhaps a way to round with whatever units are already on the number?

Here is my current code, which only works if your studio is english.

roundToPrecision( result / inch, 1);

kevin_o_toole_1

@MichaelPascoe
ValuesWithUnits are agnostic to the unit type (they can more correctly be thought of as values with dimensions e.g. length, not units e.g. inches).

So no, there is no difference between setting a parameter value to "1 in" vs. setting it to "2.54 cm".

Sounds like you want code that does do different things for those two values, which smells a bit off. For instance, if you're trying to get two different units to compare equal, tolerantEquals() is definitely preferable to rounding both.

Granted, if you're interested in an end user output, correct units are definitely good. There's a couple ways to display values with units natively in Onshape:
- If you're trying to inform the user of an output value, you can use a READ_ONLY parameter to display it
- If you want many such outputs, a custom table can display those

And if you really do just need such a thing in the code, there is also a sneaky workaround where you can capture the default units of the workspace (at the time a feature was created) with an ALWAYS_HIDDEN length parameter with known defaults for each unit type.

MichaelPascoe

@kevin_o_toole_1
Thank you for the explanation and examples. This is very helpful!

Ah, I like the work around.

MichaelPascoe

For anyone who may need this work around for rounding, I used what @kevin_o_toole_1 showed me and implemented it into my feature with a few changes.
 Variable (Advanced)

Like Kevin said, this will capture the default units of the workspace at the time a feature was created. 

precondition { annotation { "Name" : "Rounding / Precision", "Default" : RoundingPrecision.ONE_THOUSANDTH } definition.roundingPrecision is RoundingPrecision; //Get work space units work around. Reference kevin_o_toole_1 //https://forum.onshape.com/discussion/comment/43969#Comment_43969 annotation { "Name" : "Invisible length", "UIHint" : UIHint.ALWAYS_HIDDEN } isLength(definition.invisibleLength, { (inch) : [-10000, /* min (inclusive) */ 1.0, /* default */ 10000 /* max (inclusive) */], (meter) : 1, (centimeter) : 1, (millimeter) : 1, (foot) : 1, (yard) : 1 } as LengthBoundSpec); } { const units = definition.invisibleLength; var unitMultiplyer = switch (units) { (inch) : inch, (meter) : meter, (centimeter) : centimeter, (millimeter) : millimeter, (foot) : foot, (yard) : yard, }; var unitlessValue = definition.value / unitMultiplyer; var value = roundToPrecision(unitlessValue, 2); value = value * unitMultiplyer; setVariable(context, definition.name, value); setFeatureComputedParameter(context, id, { "name" : "d", "value" : value }); });

 

EvanReese

Thanks for the writeup Kevin. I've been following along because I still get hung up on units stuff sometimes.

Chris_D_Mentes_001

BTW @kevin_o_toole_1 can we please have the "round(length, millimeter)" syntax added to the documentation: https://cad.onshape.com/FsDoc/library.html#roundToPrecision-number-number
I also noticed that the min() and max() functions accept valueWithUnit types which isn't specifically mentioned. This is minor stuff but always better to be thorogh in documentation

Chris_D_Mentes_001

Holy crap I'm glad I wrote that post over a year ago hahaha, I've completely forgotten I figured it out. Still have no idea how or why it works.
round funciton can be used to round value with units