Defining a point on a sphere

[lococnc]

When creating a point on a sphere Pro/E lets you define only two offset references.

This is silly, it does not fully define the position of the point and it is making an assumption that it is not letting me define.

How do you fully define the position of the point on the sphere?

[DeanLong]

Hi Michael,

Pro is really not making an assumption at all. The sphere you created is contrained at it's dimensional values. When you place the point on the sphere you have created the point'sfirst contraint by default by the sphere's diameter. The two additional drag handles are actually the second and third contraints.

You could add the point first with X. Y and Z coordinates and then create the sphere through the point.

Dean

In Reply to Michael Gamber:

When creating a point on a sphere Pro/E lets you define only two offset references.

This is silly, it does not fully define the position of the point and it is making an assumption that it is not letting me define.

How do you fully define the position of the point on the sphere?

[kdemont]

Couldn't there be two points in space that couldbe on the surface of a sphere if only two other constraints are defined?

[bfrandsen]

The two dimensions available constraints the point to a line in space. A
line can cut a sphere in two locations, so ProE must do an assumption to
which of the two it uses. In ProE a sphere is created as two half spheres,
so my guess is that the halfsphere selected determines the location.
An interesting test would be to make a 359 deg revolved sphere as it will
only consist of one surface, but will still have two possible point
locations. Will a third dimension constraint be available?

/Bjarne



Dean Long <->
12-02-2010 23:26
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Dean Long <->


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[proecad] - RE: Defining a point on a sphere






Hi Michael,
Pro is really not making an assumption at all. The sphere you created is
contrained at it's dimensional values. When you place the point on the
sphere you have created the point's first contraint by default by the
sphere's diameter. The two additional drag handles are actually the second
and third contraints.
You could add the point first with X. Y and Z coordinates and then create
the sphere through the point.
Dean

In Reply to Michael Gamber:

When creating a point on a sphere Pro/E lets you define only two offset
references.

This is silly, it does not fully define the position of the point and it
is making an assumption that it is not letting me define.

How do you fully define the position of the point on the sphere?

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[dgallup]

Latitude and longitude are sufficient to uniquely define every point on earth. I think you might be better off using a spherical coordinate system for your references.

[DanMcCaherty]

"Latitude and longitude are sufficient to uniquely define every point on
earth. I think you might be better off using a spherical coordinate
system for your references. "

I think the problem is that Pro/E doesn't allow you to specify whether or
not the latitude is north or south of the equator.

[dgallup]

Sure it does, with a spherical csys.

In Reply to Dan McCaherty:

"Latitude and longitude are sufficient to uniquely define every point on
earth. I think you might be better off using a spherical coordinate
system for your references. "

I think the problem is that Pro/E doesn't allow you to specify whether or
not the latitude is north or south of the equator.

[davehaigh]

This may be of more use.

Here are the proE relations to convert between spherical and Cartesian coordinates: (These assume +Z is the pole and XY are the equator)

Spherical to Cartesian:
X=rho*sin(theta)*cos(phi)
Y=rho*sin(theta)*sin(phi)
Z=rho*cos(theta)

Cartisian to Spherical
Rho=sqrt(x^2+y^2+z^2)
Theta=atan(sqrt (x^2+y^2)/z)
Phi=atan(y/x)

Rho to cylindrical radius
R=rho*sin(theta)

David Haigh
Phone: 925-424-3931
Fax: 925-423-7496
Lawrence Livermore National Lab
7000 East Ave, L-362
Livermore, CA 94550