Finding the Center of a Spherical Surface

Use a 3D sketch to place two points anywhere on the spherical surface (use coincident constraint between point and surface). Create axes through the points and normal to the surface. The intersection of two axes will give you the spere center.

Assuming the map is projected onto a sphere and not on an Elipsoid (since the earth is not a true sphere). Another way to tackle this may be to:

1. Copy the spherical surface (surface offset at zero)
2. Use a surface untrim on that surface. You may need to up the percentage.
3. A couple options: You can repeat step 2 with high percentages until the surface turns into a sphere, but it may not be neccessary: Notice that the surface untrim should create two (of the four) edges that are planar to the center of the sphere. Create a plane using the end points and midpoint of one of those edges. This will create a plane running through the center of the sphere. Open a sketch on that plane and convert the edge into a arc. This should locate the center.

I mocked this up and imported similar data into solidworks and it worked.

Hope it works for you.

Dan S.

Try this,

Create a plane intersecting the spherical surface, then select that palne and use Tools/Sketch Tools/Intersection Curve. That gives you a planar scetch with an intersection curve. The center of that curve is the center of the sphere.

snipped-for-privacy@yahoo.com wrote:

How can you be sure the plane intersects the center?

You're right, you have to make sure that a normal vector to the surface is on that plane. Easy way to check that is to try to dimension the intersection curve. If SW recognizes it as an ark (not as an ellipse) it means you're sectioning thru the center.

Your approach (3d sketch & 2 axes) works faster. I just tried it.

Here's an example based from the responses.. (I actually did it last night but did not have time to send it)