Difference between .LineTo and sketch.LineTo

[raydeleu]

To clarify the concept of parametric modelling I wanted to create a shape governed by a mathematical equation. As an experiment started to reproduce some work I found on the internet to model the Gherkin Tower in London. I started with a simple revolve of a sketch like this:

// points on contour
let p0 = [.13 , 0   ]
let p1 = [.20 , .66 ]
let p2 = [.11 , .80 ]
let p3 = [.03 , 1 ]
let p4 = [ 0  , 1 ]

// create a sketch of the contour and close it
let profileGherkin = new Sketch(p0)
.BezierTo([p1,p2,p3,p4])
.LineTo([0,0])
.LineTo(p0)
.End().Face(false)

// revolve the sketch 
Translate(  [70,0,0],
            Rotate( [1,0,0],90,
                Revolve(
                        Scale(180,profileGherkin)
                            ,360,[0,1,0], true, true
                        )
                    )
        )

As I figured that interpolating the points on the spline would not be easy, I searched for an equation to describe the contour. I found a proposal for this equation at https://prezi.com/ag4kjn9i1upt/the-gherkin/ and converted this into the following code:

function equationGherkin(x) 
{
    let pt1 = x*x - 144*x + 5184;
    let pt2 = pt1 / 11664;
    let pt3 = 1-pt2;
    let pt4 = Math.sqrt(pt3);
    let y   = 28.25 * pt4;
    return y
}

// evaluate the function starting a height h=0
let h = 0;
let c0 = [equationGherkin(h),h];
let calculatedGherkin = new Sketch(c0)

for (let hi = 1; hi <= 180; hi+=1)
{
    calculatedGherkin.LineTo( [ equationGherkin(hi) , hi])
}
calculatedGherkin.LineTo([0,0])
calculatedGherkin.LineTo(c0);
calculatedGherkin.End();
calculatedGherkin.Face();

// revolve the sketch 
Rotate( [1,0,0],90,
        Revolve(calculatedGherkin
                ,360,[0,1,0], true, true
                )
        )

The sketch seems to complete without a problem, but as soon as I feed it to the revolve function I get the error Line 52: Revolve() encountered function signature mismatch. The more elaborate error message (found after pressing F8) is

Argument of type Sketch is not assignable to parameter of type 'TopoDS_Shape'. Type 'Sketch' is missing the following properties from type 'TopoDS_Shape': IsNull, Nullify, Location, Located, and 27 more.(2345) .

It seems that by using the form sketch.LineTo I get a different result from the direct continuation of .LineTo after the initiation of the sketch. I confirmed this by changing the first example to resemble the second one. It get's broken too after adding the sketch name in front of the .LineTo. What do I miss?

[zalo]

Actually, the culprit is the .Face() function, which returns a TopoDS_Face rather than a Sketch object.

The fix is simply to move calculatedGherkin.Face() from its own line into the Revolve function's signature 👍

[raydeleu]

Thanks, this indeed works. I have to figure out how to explain this properly in the manual. I tried to check what type an object is with the function "typeof" but this simply returns it as "object".