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## #1 2012-04-20 19:20:35

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Area of Polygon by Drawing

A new app tentatively titled: Area of Polygon by Drawing

Does the title make sense? It can also double as a "solving" tool if you know enough lengths/angles.

Converting back/forth between the mouse coords (in pixels) vs graph coords (which the user can vary) kept on going wrong, but I think it is good now.

Have a play, let me know how it goes.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #2 2012-04-20 20:29:53

bob bundy
Registered: 2010-06-20
Posts: 8,323

### Re: Area of Polygon by Drawing

hi MathsIsFun,

Another great page.  Well done!

Haven't found any bugs yet.

Question:  When adding a new point, what is your criteron for where it is placed?

And:  Do I have to move my points with the mouse or is there a way to move with arrow keys or even specify a pair of coordinates exactly.

I see, for example, that your default shape is a regular pentagon.  Supposing I wanted a regular hexagon?

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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## #3 2012-04-20 21:12:49

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Hi MIF;

A very good idea! I kind of like it.

I would like to have more digits.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #4 2012-04-20 22:16:19

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: Area of Polygon by Drawing

New point: half way between first 2 points.

Good suggestions. I can't figure how to implement at the moment, but will note them down.

bobbym wrote:

I would like to have more digits.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #5 2012-04-20 23:57:03

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Hi MIF;

Hmmmm, those are fine. What would be nice is a few more digits for the area and points.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #6 2012-04-21 02:39:05

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

I like it,but it cannot be moved left,right,up and down.

I am amazed to how many digits I was able to zoom in.

Last edited by anonimnystefy (2012-04-21 02:39:17)

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #7 2012-04-21 10:17:21

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: Area of Polygon by Drawing

anonimnystefy wrote:

I like it,but it cannot be moved left,right,up and down.

Click on left of drawing surface to "recenter" half way to right.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #8 2012-04-21 10:24:34

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

I'll try that tomorrow.

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #9 2012-04-22 13:18:48

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: Area of Polygon by Drawing

Try putting in (4,6), (2,6), (2,4), (4,4), (4,2), (6,2), (6,4), (8,4), (8,6), (6,6), (6,8), (4,8) for a positive experience.

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #10 2012-04-22 13:29:43

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Hi MIF;

That is a neat feature.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #11 2012-04-22 14:22:31

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

I am not sure what that is,but I think it is a:

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #12 2012-04-22 16:11:44

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: Area of Polygon by Drawing

Yes, anonimnystefy, A+

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #13 2012-04-22 17:04:22

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

A winner is me -.-"

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #14 2012-05-13 19:58:45

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: Area of Polygon by Drawing

New version 0.75

Linky (same as above)  Area of Polygon by Drawing

Has a "Regular" button (to make it regular, of course). A bob bundy request.

Also includes a description of the polygon: regular, concave, complex. Let me know if it gets it wrong!

Also try to make a regular polygon without using the regular button

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #15 2012-05-13 21:08:37

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Hi MIF;

Seems to be working nicely.

I use a formula involving determinants for the computation of areas. What do you use?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #16 2012-05-13 22:56:44

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

Hi bobbym

Is that the shoelace formula you are using?

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #17 2012-05-13 22:59:00

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Sorry, I can not even remember what day it is and you want me to remember what these formulas are called?

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #18 2012-05-13 23:04:34

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

Did you try searching "shoelace formula" to see if that is the one?

Btw,today is 14/5/2012,Europian date format.

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #19 2012-05-13 23:12:35

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Heck no! That is most convoluted idea I have ever seen. I just plug them into a big matrix and let M get the determinant.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #20 2012-05-13 23:14:27

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

Plug what into a big matrix?

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #21 2012-05-13 23:15:28

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

The coordinates.

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #22 2012-05-13 23:16:16

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

What kind of matrix? What are the dimensions?

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

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## #23 2012-05-13 23:17:59

MathsIsFun
Registered: 2005-01-21
Posts: 7,684

### Re: Area of Polygon by Drawing

bobbym wrote:

I use a formula involving determinants for the computation of areas. What do you use?

Same, really. Sum up (pt0.x * pt1.y - pt0.y * pt1.x) for successive pairs of points (including last to first). Need to divide by 2 at end.

Couldn't work out how to get area for complex shapes, though, so just say "complex".

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #24 2012-05-13 23:20:56

bobbym
bumpkin
From: Bumpkinland
Registered: 2009-04-12
Posts: 109,606

### Re: Area of Polygon by Drawing

Sorry, I seemed to have dropped the determinant way in favor of some algorithm. This is the one I have in my notes right now. I was wondering what MIF is using

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

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## #25 2012-05-13 23:21:34

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

### Re: Area of Polygon by Drawing

Does the same method work for complex polys?

Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Offline