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Ellipse plotted by Polar Equation gets slightly off from its focus.

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Hello, I am plotting ellipse on XY graph by using LabVIEW 2019.  

To generate coordinates for plotting ellipse, polar equation is used, which is the same one as this (relative to focus).  

With this equation, one focus is fixed at origin (0,0), the other is given by control on front panel.  ("focus X" and "focus Y")  With these two focuses, "semi-major" length is the last parameter to determine the elliptic shape.  Below is the block diagram on which the equation is executed.  

 

polar equation elliptic plot by LabVIEW (block diagram).png

Then,  I get results as follows.  

polar equation elliptic plot by LabVIEW.png

The major-axis drew in black is added by MS Paint later, and the line in red between two focuses is slightly off from the major-axis.  

 

I triple-checked the equations, and spent couple days to find out the cause of this offset, but could not solve it yet.  

 

Would somebody please help me to solve this problem??

 

 

Best regards,

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Solution
Accepted by topic author UMASO

Sorry if somebody has already taken a look at my question above, but it looks like the offset stems from the aspect ratio of XY graph... 

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@UMASO wrote:

Sorry if somebody has already taken a look at my question above, but it looks like the offset stems from the aspect ratio of XY graph... 


http://zone.ni.com/reference/de-XX/help/371361R-0113/lvprop/grphchrt_plot_areaszewdth/

 

 

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