Custom Trapezoid Question

[Hans Wiederrich]

New Affinity Designer user here.

I would like to create a trapezoid with specific dimensions and rounded corners.  Could someone please let me know the best techniques for that?  Thanks!!

reate a trapezoid with the following dimension: 

[NotMyFault]

I would use school geometry and helper objects

1. create trapezoid of larger horizontal size x rough size of vertical line

2. use helper rectangular shape object in size of lower edge to set correct size accordingly

3. use circle with 2x size of intended height centered over upper right corner to set correct height of trapezoid

[Hangman]

Hi @Hans Wiederrich and welcome to the forums,

Indeed, a bit of old-school geometry should do the trick...

When creating a Trapezoid using the Trapezoid Shape tool you can define the following criteria...

 

• We know the Trapezoid's longest and shortest horizontal widths, i.e., 2.75" and 2.5"...
• We know the measurement for the hypotenuse of the yellow right-angled triangle, i.e., 1.375"...
• We know the measurement for the base of the yellow right-angled triangle i.e., ((2.75 - 2.5) /2) = 0.25"
• We need to calculate 'a' i.e., the height of the Trapezoid...

Applying Old School Geometry

• Hypotenuse² = Height² + Base²

So

• Height² = Hypotenuse² - Base²
• Height² = 1.375² - 0.125²
• Height² = 1.890625 - 0.015625
• Height (a) = sqrt 1.875"
• Height (a) = 1.36930"

This means we can use the Trapezoid tool to create a Trapezoid shape with a:

Width of 2.75"
Height of 1.36930"
Left Point of (((0.25" / 2.75")) / 2) x 100 = 4.545455%
Right Point of 100% - 4.545455% = 95.45455%

Rotate by 180° and then apply rounded corners to suit using the Corner tool...

[R C-R]

What I think should work but does not is

1. Create a circle with a 1.375" radius (so a 2.75" X 2.75" ellipse).
2. Create a straight horizontal 2.75" long line with the Pen Tool & snap it to the center of the ellipse.
3. Duplicate the line & set its width to 2.5" centered on the first line.
4. Move straight it down until it snaps to the lower edge of the ellipse.

This should create the top & bottom of the trapezoid properly positioned but it fails I believe because the Ellipse too can't create a perfect circle, which can be confirmed with the AD Measure Tool -- the radius is 1.375" only at 4 points.

Please ignore this.

Edited September 13 by R C-R

[GarryP]

As an alternative to the advice given above, and assuming that the dimensions you gave are of the trapezoid before the corners are taken into account (otherwise the maths is beyond me at half past eight in the morning), you can do what I show in my attached video.

Note 1: Document UOM should be in inches.

Note 2: 0.375 = 3/8 (Or you can just enter 1+(3/8) as the value).

Note 3: You may need to enable certain snapping options to snap the bottom line to the centre of the shape as I do in the video.

[Hangman]

8 hours ago, R C-R said:

This should create the top & bottom of the trapezoid properly positioned but it fails I believe because the Ellipse too can't create a perfect circle, which can be confirmed with the AD Measure Tool -- the radius is 1.375" only at 4 points.

It all depends on whether the 1 3/8" in the original drawing refers to the length of the angled sides (i.e., the hypotenuse of the created triangle) or simply the height of the trapezoid...

I've assumed the former in the previous post but if it is the latter then the Trapezoid tool with the following settings gives you everything you need...

 

Trapezoid

[R C-R]

6 hours ago, Hangman said:

14 hours ago, R C-R said:

This should create the top & bottom of the trapezoid properly positioned but it fails I believe because the Ellipse too can't create a perfect circle, which can be confirmed with the AD Measure Tool -- the radius is 1.375" only at 4 points.

It all depends on whether the 1 3/8" in the original drawing refers to the length of the angled sides (i.e., the hypotenuse of the created triangle) or simply the height of the trapezoid...

My assumption was it was the first, not simply the height. But as I said, it should be possible to use a circle with a radius of 1.375" to locate where the lower line should be placed. Try that with this  file & if you use the AD Measure tool you will see that the green ellipse (named "1.375" radius circle") is not a good enough approximation of a true circle for this to work.

EDIT: Never mind! I wasn't thinking about this correctly.

[Hangman]

25 minutes ago, R C-R said:

My assumption was it was the first, not simply the height.

I'm glad that assumption wasn't just mine though we could both be wrong...

26 minutes ago, R C-R said:

But as I said, it should be possible to use a circle with a radius of 1.375" to locate where the lower line should be placed.

That wouldn't work becuase you're measuring a i.e., the radius of the circle which is 1.375".

To obtain the correct measurment for a you'd apply Pythagorean theorem c² = a² + b² where we know the value of c = 1.375" and b = 0.125" ((2.75" - 2.5") /2)...

a = Height, b= Base and c = Hypotenuse

• Hypotenuse² = Height² + Base²
• Height² = Hypotenuse² - Base²
• Height² = 1.375² - 0.125²
• Height² = 1.890625 - 0.015625
• Height = sqrt 1.875"
• Height = 1.36930"
   

So you're circle would need a diameter of 1.36930" x 2 = 2.7386"

[R C-R]

4 hours ago, Hangman said:

That wouldn't work becuase you're measuring...

Yes, I realized I was doing it wrong so I struck out all that stuff on edit.