Android Question How can I calculate the actual areas from a polygon?

[Wolli013]

If I have a rectangle, a square and a trapezoid in a polygon, how is it possible to calculate and output them individually from an open shape?
Attached code how I currently calculate the base area of a room.

Sub CalculateFloorArea_orginal() As Double
    
    If walls.Size < 3 Then
        Log("Nicht genug Wände für eine Flächenberechnung")
        Return 0
    End If
    
    Dim area As Double = 0
    Dim n As Int = walls.Size

    For i = 0 To n - 1
        Dim wall1 As Map = walls.Get(i)
        Dim wall2 As Map = walls.Get((i + 1) Mod n)
        
        Dim x1 As Double = wall1.Get("x")
        Dim y1 As Double = wall1.Get("y")
        Dim x2 As Double = wall2.Get("x")
        Dim y2 As Double = wall2.Get("y")
        
        Dim partialArea As Double = x1 * y2 - x2 * y1
        area = area + partialArea
    Next

    area = 0.5 * Abs(area)
        Log("Berechnete Gesamtfläche: " & area)
            
    Return area

End Sub

 

[MasterGy]

Hello!

How precise do you have to be?
If you really need to get into the math, then instead of the Gaussian area calculation, you can perhaps divide the plane into triangles. But that is another, more complicated solution.

If you want to avoid more complicated math, I would draw the polygon on a bitmap, paint its area, and count how many pixels are painted.

 

[Wolli013]

nally, the calculations I am currently performing with the code are pretty accurate.
But I need the breakdown into the specific area types because I need to show how the final result was obtained. That's why I'm looking for such a decomposition in the individual areas to output them later.

 

[klaus]

Sorry, but I do not understand what exactly you are looking for.

If I have a rectangle, a square and a trapezoid in a polygon

What do you mean with this : rectangle in a polygon ?
Do you want to split a polygon into 'simple' surfaces or what else ?
I suppose that 'walls' is a List.
What does it contain ?
Then you use:

Dim wall1 As Map = walls.Get(i)

Why a Map ? What is this for ?

 

[Wolli013]

What do you mean with this : rectangle in a polygon ?
Do you want to split a polygon into 'simple' surfaces or what else ?

YES

 

[Wolli013]

Here is an example:
There is now a rectangle and a square.
Now I would like both to be found and calculated and displayed individually according to the known formulas for area calculation, to prove how the dimensions come about.

 

[klaus]

Well, i am afraid this would be very complex. I have no idea how to do it.
Depending on the complexity of the polygon.
And why do you want this ?

 

[klaus]

Now I would like both to be found and calculated and displayed individually according to the known formulas for area calculation, to prove how the dimensions come about

Why ?

to prove how the dimensions come about.

Are you not sure of the calculation of the total area ?

 

[Wolli013]

But I am sure and the surfaces also fit.
But for a measurement program, these areas must be shown individually.

 

[klaus]

But for a measurement program, these areas must be shown individually.

What kind of measurement program ?
How are the room surfaces defined ?
Couldn't these be directly defined with a kind of set of 'elementary' subsurfaces ?
And then you can do whatever you want.

 

[Wolli013]

It is only a matter of dividing the base area into the specific shapes that are created by measuring the space in the round.

 

[MasterGy]

It is only a matter of dividing the base area into the specific shapes that are created by measuring the space in the round.

and if several solutions are possible? search for all possibilities ?

 

[klaus]

It is only a matter of dividing the base area into the specific shapes that are created by measuring the space in the round.

This is what i meant with 'a kind of set of 'elementary' subsurfaces', can't those be defined during the measurement.
One rectangle, then a second one and even others.

 

[Wolli013]

Thanks for the tip, I'll have to see how something like this can be implemented.

 

[Johan Schoeman]

Might be worth looking at this if you have the coordinates of the vertices

Area of a polygon algorithm - Math Open Reference