Hello,

I want to build a simple 3D form who look like a bridge.

Description :

• i have a bezier simple arc who are extrude for transform this arc to a
  bridge

I want than the middle of this bridge are more narrow than begin and end.
What the prefered way for doing that ?

Thanks

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I have find this about the global 3D form :
https://www.mathcurve.com/courbes2d.gb/croixdemalte/croixdemalte.shtml

And i wan't this like a bridge.

Who could i do that ?

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Like this?
http://forum.openscad.org/file/t1309/arch.jpg

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Thanks, yes, it's seem ok.
I have just a problematic point :

• i need to have the middle of this shape more narrow than the begin and the
  end.

Is it possible with your proposal ?

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Thanks for this code, it's exactly look like what i want.

I have look for my ideal parameters.
I have change those like that :
db = 20;  // diameter of bridge -- higher is flatter
dw = 40;  // width of bridge -- higher is wider
do = 1.2;  // offset of either side in the middle

I have a little bug (screenshot).

I try to understand your code proposal :
http://forum.openscad.org/file/t2049/2017-11-27_1243.png

• i have a cube minus
• • two cylinder (left and right)
• • one cylinder (down)
• • one cylinder (top)

If my understand are exact, i have just to change the compute of left &
right cylinder.

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Yes, just difference two more cylinders.
http://forum.openscad.org/file/t1309/arch2.jpg

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Thanks a lot, it's perfect.

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I have change your code like following.
Now, i just have to destroy (if possible) the x, y, z correction
and applicate my parameter like shape_Length, shape_Width, shape_Height,
bridge_Width, bridge_Height.

Thanks again.

shapeColorTop    = "red";
shapeColorLeft    = "red";
shapeColorRight  = "red";
shapeColorDown    = "red";

shapePos_x        = 10 - 75;  // true value, correction
shapePos_y        = 10 + 45;  // true value, correction
shapePos_z        = 00 - 10;  // true value, correction

shape_Length      = 110;  // Longeur
shape_Width      = 40;  // Largeur
shape_Height      = 30;  // Hauteur
bridge_Width      = 15;  // Taille étroite du pont
bridge_Height    = 05;  // Hauteur étroite du pont

translate([shapePos_x,shapePos_y,shapePos_z]) {
difference() {
difference() {
choiceColor(shapeColorTop) {
rotate([90,0,0])
translate([0,-25,0])
cylinder(h=50, r1=65, r2=65, center=false, $fa=2);
}

    choiceColor(shapeColorDown) {
    rotate([90,0,0])
    translate([0,-11,0])
    cylinder(h=100, r1=50, r2=50, center=false, $fa=2);
    }
}

// remove the lower portion
choiceColor(shapeColorLeft) {
translate([-75,-75,-90])
cube(size=[150,100,100], center=false);
}

// make arch more narrow in center
choiceColor(shapeColorRight) {
translate([0,80,0])
cylinder(h=100,r1=100,r2=100,center=false,$fa=2);
}
    
choiceColor(shapeColorDown) {
translate([0,-130,0])
cylinder(h=100,r1=100,r2=100,center=false,$fa=2);
}

}
}

// color gesture
module choiceColor(couleur)
{
if (couleur == "default") orange() children();
if (couleur == "green")  green() children();
if (couleur == "blue")    blue() children();
if (couleur == "orange")  orange() children();
if (couleur == "violet")  violet() children();
if (couleur == "red")    red() children();
if (couleur == "postit")  postit() children();
if (couleur == "marron")  marron() children();
if (couleur == "black")  black() children();
if (couleur == "white")  white() children();
if (couleur == "human")  human() children();
}
module green()  color("LimeGreen", 0.5) children();
module orange() color("Gold", 1) children();
module blue()  color("SteelBlue", 0.5) children();
module violet() color("DarkOrchid", 1) children();
module red()    color("FireBrick", 0.8) children();
module postit() color("Cornsilk", 0.8) children();
module marron() color("Peru", 0.8) children();
module black()  color("Black", 0.7) children();
module white()  color("White", 1) children();
module human()  color("SteelBlue", 0.9) children();

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