# law without streight line for reference - reverse law+ parallel line process

#### Jazzuo

##### New member
hello

in the example i used normal law and parallel process

made laws out of white lines
and made vlue lines and green lines

but what if i had only green lines and only the blue middle line to start with, and wanted to make the top and botomn blue line.
how do i make law out of the green lines since it has no straigh one?

thank you

Jazzuo

#### MrCATIA

##### Super Moderator
I remember back in CATIA V4, Laws could be made based on Reference geometry of a line, curve, or even a surface. But it seems that with V5, the reference can only be a line. The online Help describes only using a line for the reference.

So, I don't think there is a direct way to make a Law based on the distance between two curves, such as the two green curves in your example.

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#### MrCATIA

##### Super Moderator
One method that I'd try: develop flat patterns (unfold) of the two green curves and add a straight reference line. The distance between the two green curves can be determined by the difference of the distances between the reference and the unfolded curves.

1. make a flat surface between the two green curves
2. unfold the surface into a plane, and unfold both green curves
3. draw a line in the plane somewhat parallel to the unfolded lines (this will be the reference line)
4. make two Laws: Law1(D2) between the reference line and the first unfolded line, Law2(D1) between the reference line and second unfolded line
5. add a parallel curve from the blue line using Law1
6. add a second parallel curve, in the opposite direction, from the first parallel line using Law2. This should be the curve you're looking for.

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#### Jazzuo

##### New member
Hi i understand what you are trying to say, but i am unable to do it in catia
by step num 2 i just get a surface turned 90 degree not a straigthen out worm

J