# Draw arc in scatter graph from arc radius & arc length

#### Charmwah

##### Board Regular
Afternoon all...

...I'm trying to use the scatter graph to draw out the extent of an arc, for which I know the radius and the length of the arc itself. These are the only two 'knowns' I have, but from these I can of course work backwards to understand the length of the arc in degrees etc. What I'm struggling with is a way to populate a table of Cartesian X,Y coordinates from which I can then plot the arc perfectly in the graph without it sloughing off as below (it should form a perfect arc, not :

Any and all help gladly recieved!

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#### Habtest

##### Board Regular
With the condition the arc starts on Y axis and go clockwise no more than 90 degree. You may want to define an interval degree of 5-15, sort the coordinates, and finally adjust the axis range and size. The rest is math.

Cell Formulas
RangeFormula
C2C2=PI()/1.5
C6:C25C6=SQRT(\$C\$1^2-B6^2)
B7:B25B7=MIN(\$C\$1*SIN(ROWS(B\$6:B6)*\$C\$3*PI()/180),SIN(\$C\$2/\$C\$1)*\$C\$1)

#### Charmwah

##### Board Regular
Thanks Habtest, but that doesn't work with my variables of an arc radius of 5.7m & an arc length of 1.19m (or 12°)...

With the condition the arc starts on Y axis and go clockwise no more than 90 degree. You may want to define an interval degree of 5-15, sort the coordinates, and finally adjust the axis range and size. The rest is math.

Cell Formulas
RangeFormula
C2C2=PI()/1.5
C6:C25C6=SQRT(\$C\$1^2-B6^2)
B7:B25B7=MIN(\$C\$1*SIN(ROWS(B\$6:B6)*\$C\$3*PI()/180),SIN(\$C\$2/\$C\$1)*\$C\$1)

View attachment 36843

#### Charmwah

##### Board Regular
Its the axis sizes that are the problem here isn't it? Thats whats skewing the arc. So how do I set those to ensure the arc is always perfect, as it should be from the maths?

#### Habtest

##### Board Regular

Thanks Habtest, but that doesn't work with my variables of an arc radius of 5.7m & an arc length of 1.19m (or 12°)...

View attachment 36844
Yes. Could be slightly different depending on your excel version (would be good to update that part in your account profile), try right each axis figure area, and edit axis bound accordingly as below (both 0~Radius or a little more).

Yes

#### Charmwah

##### Board Regular
But is there a way to do this automatically? From a bit of Googling it looks like its a case of manual resizing the axis each time, since both X & Y need different values in order to make the grid 'square' as opposed to skewed to rectangular as is the default...
Yes. Could be slightly different depending on your excel version (would be good to update that part in your account profile), try right each axis figure area, and edit axis bound accordingly as below (both 0~Radius or a little more).

View attachment 36927
Yes

#### Habtest

##### Board Regular
Maybe automating the sizing via VBA, though not any I know of.

#### Charmwah

##### Board Regular
Maybe automating the sizing via VBA, though not any I know of.
As i thought. Thanks for your help anyway, greatly appreciated!

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