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lococnc1-Visitor
1-Visitor
February 12, 2010
Question

Defining a point on a sphere

  • February 12, 2010
  • 7 replies
  • 2172 views

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?

    7 replies

    D
    DeanLong1-Visitor
    1-Visitor
    February 12, 2010

    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?
    K
    kdemont1-Visitor
    1-Visitor
    February 13, 2010
    Couldn't there be two points in space that couldbe on the surface of a sphere if only two other constraints are defined?



    B
    bfrandsen10-Marble
    10-Marble
    February 15, 2010
    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
    Please respond to
    Dean Long <->


    To
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    cc

    Subject
    [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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    D
    dgallup1-Visitor
    1-Visitor
    February 15, 2010
    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.
    D
    DanMcCaherty1-Visitor
    1-Visitor
    February 15, 2010
    "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.
    D
    dgallup1-Visitor
    1-Visitor
    February 15, 2010
    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.
    D
    davehaigh13-Aquamarine
    13-Aquamarine
    February 16, 2010
    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

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