# Command: _Patch

## In help file: Patch Surface Options: “Sample point spacing” The nominal 3-D distance between points sampled from input curves. Minimum of 8 points per curve.

[Question]
I am difficult to understand what “the nominal 3-D distance” means.

I thought to “the nominal 3-D distance” = Straight-line distance?
Did I understand correctly?Patch.zip (19.3 KB)

I think in this case it means “approximate”… The distance between points will be close to the value indicated, but not necessarily exact.

–Mitch

It’s more difficult to understand.

@lowell, What does this mean, exactly?

What Mitch said. The curve is divided into equal spaces to give close to the specified spacing.

Not Lowell, but to me (maybe I’m wrong), Patch is fitting the surface to points sampled along any curves and not the curves themselves. In dividing a curve, if you input a fixed length, there will be an odd division left at the end. If you want the curve to be divided in even intervals all the way along from start to end, you then expand or contract the specified distance a little to allow that to happen. Thus the “nominal” distance (the one you specified) is not the exact distance, but it’s the nearest close possibility…

–Mitch

Ahh, the telephone rang while writing this and Lowell beat me to it…

What does the sample point spacing mean?
The Distance between sample points?
or
The Length between sample points?

The most logical would be length along the curve - also simpler to program - so I expect it’s that…

–Mitch

Final decision:

I thought…

The sample point spacing:
Not parametric distance but physical distance(Arc length) along the curve.

Is it right?

Probably - I’m not the programmer. But parametric distance would vary along the curve according to parametrization, so again logical would be physical distance… I’ll let @lowell or Dale answer this definitively though…

–Mitch

It is distance along the curve, but if you’re using spacing big enough for that to matter, you won’t get what you want anyway so its really not significant which it is.
In your example above there are relatively big areas of the green curve about which you have no information, meaning Patch won’t be trying to fit to those parts of the curve.

In help file: Rhino V2, V3, V4, V5.

Sample point spacing:
The nominal 3-D distance between points sampled from input curves.
Minimum of 8 points per curve.

It is always the same explanation over 10 years.
I think that this description is hard to understand.

So, I want to understand it correctly now.

“It is distance along the curve.” = “physical distance(Arc length) along the curve.”
Is it right?

Yes. I will change the Help. Thanks.
Bug #http://mcneel.myjetbrains.com/youtrack/issue/RH-22964 (not yet visible to public)

I hope to it had attached reference image and swf (not only text explanation).
I really appreciate it.