Extracting nodal coordinates- x,y,z; r,theta,phi;r,theta,z

[SuG89]

Hello everyone,

I am using two different local coordinate systems- spherical and cylindrical. The nodal coordinate list is displayed in Cartesian coordinates by default.

When I list the nodal coordinates (using DSYS,local coordinate number before listing), I don't get the radial coordinate as a constant value. I don't understand why this is happening because the radius is a constant value of 5 meters. Could anyone tell how can I correct this?
_________________
Best regards,
Sushant Goel
MSc Uni Stuttgart

 

[rb1957]

maybe the origins of the two systems aren't co-incident ?

it's pretty easy math to convert from one co-ord system to the other. do the math yourself, then try to figure out what your software is doing.

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[SuG89]

https://www.dropbox.com/sh/sib7ehoen5gvcnb/AAB2FhQwHE0B2Ufe7wjUff66a?dl=0

The two files uploaded at this link show nodal coordinates for DSYS,0 and DSYS,12 (spherical). The value for radius is 5385.16mm (not 5000mm) which matches with the formulas given for coordinate system conversion. But the theta and phi values do not match with the given formulas.

Does anyone has suggestions on how to correct these discrepancies?

Best regards,
Sushant Goel
MSc Uni Stuttgart

 

[rb1957]

why don't you apply the conversion you've provided to the cartesian co-ord data and see what you get. hint, i get the same radius as the Dsys 12 data. i'm not sure your conversion will give the right angles (just saying "i'm not sure") ... looking at arccos (z/r) ... there are two solutions (they are? 180deg apart so it might merely be a matter of CW or CCW ?)

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[SuG89]

Yes I applied the formulas before and radius was matching. The angles were not matching at that time. I'll check again in regard to CW and CCW and update here.

Best regards,
Sushant Goel
MSc Uni Stuttgart

 

[rb1957]

try it with some simple points, one in each quadrant (eight altogether).

have you resolved why the r isn't what you expected ?

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[SuG89]

Hi,

I just figured out the problem. The radius of my spherical calotte (not a full sphere or hemisphere) is 7.25 meter. I moved my model location such that the distance from origin (0,0,0) to spherical calotte surface is 7.25 meter. Now I am getting the correct radius values. Didn't check the angles but they should be correct.

So, it was my mistake of wrong model location with respect to origin and considering span/2 = 10/2 = 5 meter as radius. Sorry for all the confusion.

Best regards,
Sushant Goel
MSc Uni Stuttgart

 

[rb1957]

often simple errors are caused by users ! ... i know i've done it more than once !!

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