Topic: (C3D 08) What's up with this surface?

[Guest]

I'm starting to wonder, where this surface came from? As in was it modeled; or were the contour lines drawn to represent a design that was never modeled? What do you know of the origin of these underlying 'contours', and why did you not get the terrain model from the source?  Just curious, as always.

We didn't get a DTM (as usual).  From what I understand of this project (and I'm not directly involved or doing any production work), we received the survey file from the architect (in this case, we're working for the architect directly and not the owner).  Why they named their layers FG (finish grade?) is beyond me.  I've learned to not question what architects do, because it usually doesn't make any sense anyways (at least when it comes to site plans).

But this is typical of what we'll receive for an existing survey.  If we're lucky, they might actually be contours (although contour objects seem to be pretty much uselss in C3D).  Most of the time the contours are plines with elevations (again, if we're lucky) and some spot elevations, maybe some breaklines.  We've NEVER received any of the LDT files for a terrain, and only once have we received an actual C3D model of an existing surface.

[mjfarrell]

Wow! What's up with that?  Are the engineers or surveyors afraid to give up the data? The challenge is going to be that we will not be able to reproduce EXACTLY those contours. The thing is C3D is using an algorithm to create contour lines from the data we gave it, this data is NEVER going to be the same as the data that created those contours we have a few spot elevations, however we do not have proper breaklines.  In short we do not have enough data to recreate that surface.

At some point you (we) will have to accept what the data we were given produces and go forward with the understanding that our volumes will be off slightly as the model will never be completely accurate. Unless, you can get the DTM, ask the owner to press the surveyor for this information he did pay for it and it will increase accuracy. Or you go get the original building plans and recreate the FG model from their plan using feature lines.

[Guest]

Wow! What's up with that?  Are the engineers or surveyors afraid to give up the data? The challenge is going to be that we will not be able to reproduce EXACTLY those contours. The thing is C3D is using an algorithm to create contour lines from the data we gave it, this data is NEVER going to be the same as the data that created those contours we have a few spot elevations, however we do not have proper breaklines.  In short we do not have enough data to recreate that surface.

At some point you (we) will have to accept what the data we were given produces and go forward with the understanding that our volumes will be off slightly as the model will never be completely accurate. Unless, you can get the DTM, ask the owner to press the surveyor for this information he did pay for it and it will increase accuracy. Or you go get the original building plans and recreate the FG model from their plan using feature lines.

Yeah... welcome to my world.   

If we got the LDT info, we'd simply import it and call it a day.  (right?)

[mjfarrell]

I would lean towards placing ONLY the TIN file in the C3D project, and 'create surface from TIN' and apply styles as required. Otherwise, don't drive yourself too crazy trying to replicate those contours you were given within your model. Because unless you enter the curb lines and other appurtenances your model will rarely if ever match one created from contour driven data. If you proceed further with this surface I suggest that it be named "EG-CONT" as this will remind all users that it was created from contour data.

[Guest]

If you proceed further with this surface I suggest that it be named "EG-CONT" as this will remind all users that it was created from contour data.

Good idea.

I built the surface but I've got a somewhat different display of it than you did.  In the first image, I didn't add the spots.  The second one shows spots.

[mjfarrell]

I experimented with selectively adding and removing some of those points some I like some I don't.
You may need to fake a handfull of break lines to get that drive lane to 'pop' out or accept what the model does without them.

[Guest]

I experimented with selectively adding and removing some of those points some I like some I don't.

Ahh HAA!!!  Cheater!   

You may need to fake a handfull of break lines to get that drive lane to 'pop' out or accept what the model does without them.

That was going to be my next step.

[mjfarrell]

Not Cheating, the image you saw had no points in it at all.


Was merely explaining the 'cheats' I might use given the data we have to play with.

With some hands one bets the cards.
With some hands one bets the players.

[dfarris75]

You know we've had issues with getting data from surveyors on a regular basis Mike. For some reason they are very tight with their data. I have heard excuses from "liability reasons" to "if it's not stated in the contract as part of the deliverables we don't give it" to "we don't normally give data out to engineers because they don't give us data for stakeout"

This is the sort of attitude we get from many of the surveyors here. I've been able to get some by having the boss put pressure on them. Other times I haven't and ended up using contour data and/or manually inputting points. I've only worked with two or three surveying co's who will freely give data in the 7 years I've worked in the field.

Why does it surprise you so much Mike? Are they more promiscuous  with survey data in AR.?

[mjfarrell]

I don't know perhaps I work closer to the originators of the data these days. Although the owner can and should be your ally on this. If he understands the impact of time and accuracy and that he paid for the surface model once already, they usually provide sufficient leverage to get the data.

If a Survey or Engineering company is fooling themselves into believing they are NOT liable because they do not release the digital data they are sadly deluded.
Case in point: If it is for design plans, and one recreates the plan from all data given it will result in the same level of liability as if they provided the model. It does provide a slight amount of wiggle room in your interpretation of the data as provided on the plans. Same goes for a topographic survey, if they do not have enough confidence in their work to issue the data electronically I would question their methods and practices.

As long as the client has PAID for the work all files related to the work belong to the client and the producer of said works should release to any and all as directed by the owner. 

[Guest]

UNCLE!! UNCLE!!!

I can't figure out this breakline thing.  Wanna give me a hint?

[mjfarrell]

The suggested method would be to draw a polyline along that 'crown' line that is being suggested by the contours.
Convert it into a feature line lifting the vertex elevations only, and then add it as a breakline. You may want to remove the contours first and then add them in ignoring the ones describing the drive lane.

[mjfarrell]

A few tweaks left and It will ALMOST recreate those contours we were given. I say almost because there is a WALL in the landscape area we were given NO data on.

[Guest]

The suggested method would be to draw a polyline along that 'crown' line that is being suggested by the contours.
Convert it into a feature line lifting the vertex elevations only, and then add it as a breakline. You may want to remove the contours first and then add them in ignoring the ones describing the drive lane.

I'm not an en-gin-ear so... LIFTING??!?  Please 'splain.

[sinc]

This is the sort of attitude we get from many of the surveyors here. I've been able to get some by having the boss put pressure on them. Other times I haven't and ended up using contour data and/or manually inputting points. I've only worked with two or three surveying co's who will freely give data in the 7 years I've worked in the field.

If you were in Colorado, I'd tell you to give us a call...  As it is, our field crews like to stay within an hour's drive of home for some reason...

We've actually discovered that free flow of data among all involved in a project results in a better end product at lower total cost with fewer problems and errors, which equates to happier customers and just a better environment in general for all.  But maybe in Florida it's more fun to have pissing matches and draw lines in the sand?  After all, you have all those beaches...