Pipe profile

[qchenTPPXV]

Greeting,

I have a question about superimposed profile. I projected profile A to profile B first. Then I created profile B that exactly follows profile A. However, when I project profile B into profile A's view, I found out they are not match. Do you know how to solve it? 

[stevenh0616]

Hi @qchenTPPXV 

Are the two profiles using the same Alignment? If they are different alignments with different horizontal placement, then I would imagine the two profiles would not match.

[qchenTPPXV]

They are different alignments. From my understanding, they could match as the profile A is projected to profile view B. Most of the profiles match expect three blends don't match. The total length for the station is more than 200 meters and there are more than 12 blends. Just want to know the reason that those three blends don't match.
[cid:a1a3e868-8493-43e4-b489-a5925e78ff76]

[m_kingdon]

It is hard to answer without some screenshots or the drawing to look at.  Are you able to upload the drawing file?

[stevenh0616]

Ok. You’ll have to share some photos or better the DWG for anyone to explain that.

[qchenTPPXV]

Sure.

1. I have a alignment A and profile A from consultant.

   1.  I created a new alignment  B in order to trace watermain as the alignment isn't the center line for wm.

   

   3. create a profile for alignment B and projected profile A into this.

    4.draw a new profile B that follows exactly profile A in alignment B

   5. found out profile A and B don't match in alignment A's profile view

   

   Please also see the file attached.

[m_kingdon]

I don't have time to have a thorough look into the drawing.  But I would guess that the problem is the fact that the two alignments have slightly different lengths and the offset between them varies.

For example, there would have to be distortion comparing the two profiles along this section as the offset between the two alignments changes.

[Joe-Bouza]

The problem you are faced with is length. when  profile A  is projected to profile B the point are collected perpendicular  to the station alignment of B. Imagine two points on profile A  1 from sta 1+00 and the next from station 2+00 that is 100 units apart, but they are projected tp profile B station 1+05 and 1+25. 20 units apart. 

that's the difference you are experiencing

[qchenTPPXV]

Thank you for getting back to me and explain this. I understand that because of the alignment difference, the profiles will be different. However, I draw profile B that traces profile A in Alignment B's profile view, which means, profile A and B should be the same. But they are different in alignment A/s profile view.

[stevenh0616]

Length is the issue as others have pointed out. That is where I was going with my first question. If the two alignments are different geometrically there will always be a difference.

shorter length at a given slope projected onto a longer length, will not have the same slope. So you projected alignment/profile A onto B which is longer, so the representation was not true to A. Thus reprojecting doesn’t match.

if you want the same profiles, build a flat surface to the left and the right following profile A and use that for profile B. Re-projecting to either will then match 

[qchenTPPXV]

Thank you for getting back to me. Yes, I understand that. Please let me simplify that. I have exat profile A and B in alignment B. Do you think I project profile A and B in alignment A, they should match although alignment A and B are different?

[stevenh0616 · Accepted solution]

No, not necessarily. The geometry points of Alignment A are at different locations than they are on B, so when they are projected the show up differently when relating the Profile geometry points to another Alignment's geometry. Projecting Profiles is working off the nearest horizontal placement of the Alignment you are projecting to, thus the placement of the vertical profile is not going to be the same.

[chriscowgill7373 · Accepted solution]

No they shouldnt match, because if it is an inside corner, it will pull the points closer together, if it is an outside corner it will push them further apart.  So although it matched on the inside corner, because the outside corner the stations dont exist when you have a square corner, or the points are farther apart so they wont translate the same.  You say you understand, but I dont think that you are understanding what everyone is trying to tell you.   Projected profiles stretch or shrink depending on how they relate to the other alignments.  Sometimes the shrink is not as apparent as the stretch, depending on the angle and how close the points are to each other.   Many times, to project profiles, you have to do it in multiple portions to account for the shrinkage or stretching.

[qchenTPPXV]

Thank you very much for sharing your knowledge. Yes, you are right. I tried to create a simple text and two alignments aren't match in profile A, although they are the same tin profile B. 

I have a follow-up question. How would you create the the pipe below? It is a little bit tricky. I tried to move the pipe just for couple centimeters, and it changes the angles dramatically.

[Joe-Bouza]

So I was correct?

[qchenTPPXV]

Yes, you are right. BTW, thank you very much for all of your help!