# On surface point

#### asaese

##### New member
Hello

In the command point, on surface point type, what is the role of direction option?

I have tested it. The curve on surface between the reference point and the resulted point has the same value as ditance option. But I can't notice to the relation of this curve with the direction. What's wrong?

#### MrCATIA

##### Super Moderator
The Direction defines which way the offset Distance is measured from the Reference Point. The direction is often an axis (ie X-axis), but can be any straight line.

#### asaese

##### New member
Thanks.
It is induced if we project the direction on the surface, normal to the plane tangent to the surface at the reference point, the resulted point will be layed down on this curve and the distance will be computed along this curve. Am I right? If so why isn't this true in this example?
(Provided by V5 R19)

Code:
``http://www.mediafire.com/?gcmhb8373njmlah``

#### asaese

##### New member

Code:
``````http://upload.tehran98.com/img1/qdd12y57gizuxgj2tlt.jpg

#### MrCATIA

##### Super Moderator
simple case

(still can't open your attachments, but thanks for sending them)

I've attached a simple example of how I usually use this command. Usually the Reference point already lies on the surface. And the direction is based on an Axis direction or some other line/edge I already have in my model. In my example I am creating a new point on the surface that is .500 inches away from my Reference point in the Y direction.

#### MrCATIA

##### Super Moderator
second example

Based on your description, I've created a second example using reference geometry that is NOT on the support surface:

Again, I am creating a Point on the surface that is offset .500 inch away from the Reference point, but in the direction of the line. In this case, CATIA projects the Reference point normal to the surface, and creates the new point based on the projected point. And in the same direction as the line.

The COARSE option will offset the Distance in a straight line between the points.

The FINE option will offset the Distance geodesically along the surface.

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#### asaese

##### New member
(I checked my above both attachments and personally have no issue. Besides, it's strange I'm not able to see your attached pictures! After I click on the names of them, get the following message:

asaese, you do not have permission to access this page. This could be due to one of several reasons:

Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.
)

Anyway, what I meet with my example is not the same as your statements. Step by step:
1. There is a support surface and a point on it. This point is as the reference point.
2. There is also a line parallel an axis (Y-axis for example) that goes through the referece point. This line is as the direction.
3. I create an on surface type point based on the mentioned above and a distance of 100 mm. The location of this resulted point is not meaningful for me. It is not 100 mm away from the reference point along the direction. I don't know how the location is computed?

Code:
``https://www.dropbox.com/s/fqxlewpl6lfeyjl/t3st.rar``
+

I'm sure the way CATIA computes the location of the point, is almost the same as computing the location of a Point-Direction type line when a support is defined. If I knew how the projection occurs, all would be solved. Do you know which direction the line is projected in?

#### MrCATIA

##### Super Moderator

Code:
``````http://upload.tehran98.com/img1/qdd12y57gizuxgj2tlt.jpg
I was able to open and look at the pictures you attached. But I'm puzzled by the line you are using to define the direction.

Are you just trying to understand how this program works, or do you have a design problem you are trying to solve?

#### asaese

##### New member
Yes, I am trying to know how the program works. I'm just exercising and exactly confused by CATIA.

#### MrCATIA

##### Super Moderator
I'm sure the way CATIA computes the location of the point, is almost the same as computing the location of a Point-Direction type line when a support is defined. If I knew how the projection occurs, all would be solved. Do you know which direction the line is projected in?
you are correct - it works just like the Point-Direction option for a Line, but with a support surface. Nothing is projected.

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