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River bottom surface from 3dpolyline sections?

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Message 1 of 23
Yami72
3687 Views, 22 Replies

River bottom surface from 3dpolyline sections?

Hello,

 

Can anyone tell is there an easy way to create a tin surface from 3d polylines that are generated by actual measurements of a river/ditch or imported from Hec-Ras (River Analysis -extension)?

 

The problem seems to be that the triangels should be long and narrow (like the ditch bottom in the example) instead of normal triangels the triangulation method normally generates. (The triangels in the example are generated by 3dwin -program).

 

When using Hec-Ras one way to go around this problem is to interpolate sections (XS:s) with very short distance. Hec-Ras does the interpolation very well, but I would like to have a better solution without tricks with other programs. Also in the long rivers the result is a very large file.

 

I'm using C3D 2012

 

Anyone?

 

 

22 REPLIES 22
Message 2 of 23
wfberry
in reply to: Yami72

Not sure what you are looking for?  In Civil 3D making a tin from 3D polylines cannot be much easier.  All you are showing in your dwg is the TIN.  One can only assume is that all your triangle corners are related to a field collected point.  Perhaps you can explain more.

 

Bill

 

 

Message 3 of 23
Yami72
in reply to: wfberry

Thank you wfberry,

 

Yes, maybe my explanation was a bit inaccurate. I made another example. I added two surfaces , #1 with 4 sections and #2 with 3 sections. In #1 there is not problems because sections are close each other so I can easily make a tin that represents actual river bottom quite well. This situation is found more or less only in daydreams...

 

In #2 there are 3 sections with longer distances and also curved river. Also section 2 has fewer points than sections 1 and 3. And also measured polylines are not straight in x,y plane. This situation is the every day situation.

 

In surface #2 you can see the problems. If you have different amount of points in polylines, triangulation "jumps" for example from river bottom to river bank. If you have not straight polylines, some triangels are formed only with one polyline itself. And the most diffucult situation is if you have a curved river without measured sections.

 

In Hec-Ras the section interpolation is pretty good. As you see from the attached picture, the river bottom is formed quite smoothly. Of course Hec-Ras has also limitations.

 

Now what I ask is that is there an easy way to create a tin surface from measured 3dpolylines in a way that the surface represents the actual bottom surface?

 

The ideal solution would be some kind of section interpolation along river centerline like in Hec-Ras (suggestion to the Autodesk).

Message 4 of 23
neilyj666
in reply to: Yami72

The method you are employing is fundamentally flawed when there is a large distance between sections or there is a curve in the stream. The triangular TIN is forming correctly according to the rules but it isn't necessarily what the river looks like.

 

If you have simple sections i.e. top of bank left, bottom of bank left, thalweg, bottom of bank right and top of bank right and these are the same along the river and closely spaced, then the TIN will form pretty much as expected.

 

If there are other features recorded in the sections then how does the TIN know how to form correctly? You will need to add breaklines (in plan) joining the relevant tops and bottoms of banks etc, swap triangle sides etc etc.

 

I can't see an automatic way of achieving this

neilyj (No connection with Autodesk other than using the products in the real world)
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Message 5 of 23
Yami72
in reply to: neilyj666

Yes, the triangulation does as it is programmed to do. In this case the method is not good and something else is needed.

 

In case of long and diverse rivers adding breaklines etc. manual work is a hard work to do. I also tried the new Array-command. Using the Path -method it is quite easy to copy 3dpolyline sections along river centerline. But of course you need a centerline with correct xyz-coordinates. For simple sections and rivers this is quite ok.

Message 6 of 23
neilyj666
in reply to: Yami72


@Yami72 wrote:

Yes, the triangulation does as it is programmed to do. In this case the method is not good and something else is needed.



...short of employing mind reading techniques how is the software supposed to know how the river joins up??

 


@Yami72 wrote:

Yes, the triangulation does as it is programmed to do. In this case the method is not good and something else is needed.

 

In case of long and diverse rivers adding breaklines etc. manual work is a hard work to do. I also tried the new Array-command. Using the Path -method it is quite easy to copy 3dpolyline sections along river centerline. But of course you need a centerline with correct xyz-coordinates. For simple sections and rivers this is quite ok.


This technique seems to be susceptible to "bad modelling" in that the cross section is assumed to be the same over long distances i.e. in an analogy to corridor earthworks volumes using very widely spaced cross sections in possibly varying ground topography this will derive totally misleading volumes.

 

As mentioned before, I'm not sure there is an easy way to solve this....Smiley Frustrated

neilyj (No connection with Autodesk other than using the products in the real world)
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Message 7 of 23
autoMick
in reply to: Yami72

As I understand it, HECRAS can utilise both the river path in plan view and the cross-sections to give you interpolated cross-sections that follow the river path.I don't have a solution unfortunately, however I have a few ideas that may lead in the right direction. 

 

1. "Loft" in the 3D Modelling surface tools works very nicely to interpolate (straight line path) between cross-sections. So if you have enough cross-sections along your river meanderings, then works nicely.

 

2. There are extensions for other software (e.g. sketchup) that permits "loft by rails". Once again you do it in sections, but what you do is to define the "rails" which are the left and right banks for the river and then loft the 1st cross-section to merge into the 2nd cross-section. This then gives you an accurate path of the river in plan view, and interpolates between the two cross-sections. Is there a similar way to do this in C3D?

 

3. Can't you export the hecras interpolated (as well as measured) cross-sections? If you can get these then the rest is straightforward (although only as accurate as the original data).

 

Cheers

 

- Mick

Civil3d user in Australia since 2012.
Message 8 of 23
AllenJessup
in reply to: Yami72

Maybe coming from a Surveying background I look at this a little differently. To me the answer to a problem where you don't have enough field data to model a Surface correctly is - You don't have enough field data. So in order to get a good model, you need more field data.

 

I understand field time is expensive and for a long river in may be impractical to get tight sections for the whole length. But if there are areas that can't be modeled with sections that are far apart, those areas should have sections more often.

 

If I couldn't get any more field data. I'd try using a curved Featureline for the centerline, use a stepped offset to create bottom and top of bank in the areas you don't have data. This doesn't make the model any more correct. It just makes it look better.

 

Allen



Allen Jessup
Engineering Specialist / CAD Manager

Message 9 of 23
neilyj666
in reply to: AllenJessup

Totally agree

neilyj (No connection with Autodesk other than using the products in the real world)
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Message 10 of 23
Yami72
in reply to: neilyj666

Thanks for the comments.

 

I also totally agree that a land survey is the key to the good modeling. Being on the field is quite familiar to me. But you always have to balance between costs and accuracy.

 

Thanks Mick! The loft tools seems to be a pretty handy tool for this. At least in smaller models after a short test. I read from another forum that in Inventor there is also "loft by rails" -tool. Allen's stepped offset works well in modificated channels.

 

After these comments it seems that in longer rivers the Hec-Ras interpolation is the best solution at the moment. And thanks River Analysis -extension (beta) it is easy to read all sections from the original Hec-Ras project files to 3dpolylines. Hec has its limitations and this "channel interpolation by rails" could be a good thing to develope also in C3D.

 

Message 11 of 23
neilyj666
in reply to: Yami72

I was intrigued by the "LOFT" suggestion so i tried it with some made up cross sections which worked well but the next obvious question is how can I do something with this in Civil 3D?

 

What entities can be extracted for use in Civil 3D??

neilyj (No connection with Autodesk other than using the products in the real world)
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Message 12 of 23
Yami72
in reply to: neilyj666

I found a tip to explode the loft surface, convert in to mesh and then create a tin:

http://forums.augi.com/showthread.php?123994-3D-Solid-to-3D-face-or-polymesh

 

Seems to work fine after short test. Not the most elegant process, but ok.

Message 13 of 23
autoMick
in reply to: Yami72


@Yami72 wrote:

I found a tip to explode the loft surface, convert in to mesh and then create a tin:

http://forums.augi.com/showthread.php?123994-3D-Solid-to-3D-face-or-polymesh

 

Seems to work fine after short test. Not the most elegant process, but ok.


Is this what you meant Neilyj? In other words the loft function in C3D just creates additional geometry that could be used in the definition of the surface. I think the only real advantage is that it helps to maintain a longitudinality (is that a word?) between cross-sections... but unfortuately doesn't help with interpolating between 2 cross-sections around a bend in a river.

 

If you're referring to my comment about sketchup and loft by rails, this does help with going around corners as the planform (and the varying width) of the river can be utilised if known, so that interpolation of 2 cross-sections can be achieved going around a bend. Its pretty labour intensive through. As we all know though, the cross-section of a river can and usually does change signficantly when there is a change in planform alignment, so the technical validity of doing this as a substitute for real data is highly questionable. But, once again this just generates additional geometry that could be used in C3D surface definition should it be so desired (say for visualisation purposes).

 

Regards

 

- Mick

 

Civil3d user in Australia since 2012.
Message 14 of 23
neilyj666
in reply to: neilyj666

@Yami72 and  @autoMick - I was more interested in how to use the results of the LOFT command in Civil 3D rather than specifically using it in the way that has been discussed (i.e. modelling river channels).

 

I've not really used the 3D functionality of AutoCAD (Loft, Extrude, PressPull etc etc) so was really querying the "round tripping" / interoperability of data

 

Thanks again

neilyj (No connection with Autodesk other than using the products in the real world)
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Message 15 of 23
autoMick
in reply to: neilyj666

Good point... there's about 2 million features in my 2013 infrastructure suite that I have no idea about and have never explored.

 

It would be nice if a "3D surface" created by lofting could be directly translated to a "C3D Surface", but that's probably too much to ask and if it's possible, I certainly don't know how to do it. I haven't tried the convert to mesh technique previously but will explore this. I've previously used the longitudinal splines generated by loft as "contours" for a C3D surface (loft between cross sections, explode the 3D surface to individual elements, then add contours to surface, select the splines) which was my approach to get some curvature into the C3D surface. There are probably other ways to use the 3D tools, but I stopped exploring once I got an acceptable result.

 

Regards

 

- Mick

Civil3d user in Australia since 2012.
Message 16 of 23
autoMick
in reply to: autoMick

Guys, I was playing around with this a bit more after I decided to explore some of the 3D tools a bit more - see attached. It is possible to loft between cross-sections following a river bank as a path (I didn't realise this before), then as in my previous post generate a C3D surface from the exploded splines. Doesn't overcome the lack of data in the first place, but provides what I would regard as an acceptable interpolation of what's available.

 

Sorry, I tried to post the dwg file, but it was too big.

 

Regards

 

- Mick

Civil3d user in Australia since 2012.
Message 17 of 23
AllenJessup
in reply to: neilyj666


@neilyj666 wrote:

I've not really used the 3D functionality of AutoCAD (Loft, Extrude, PressPull etc etc)



A little bit of trivia. Some these functions were actually available in LDT and Civil 3D before they made it to AutoCAD. They were undocumented and really behind the scenes. But since they were AEC products and loosely tied to ArchDesktop. You could make 3D objects that could be manipulated in many ways.

 

Allen



Allen Jessup
Engineering Specialist / CAD Manager

Message 18 of 23
neilyj666
in reply to: AllenJessup

I'll need to investigate the 3D AutoCAD functionality a bit more - I mainly use it for creating solids of circular wind turbine bases/excavation/concrete/backfilling by taking a plain CAD section drawing and revolving shapes around 360° and using MASSPROP to give volumes - works quite well...

neilyj (No connection with Autodesk other than using the products in the real world)
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Message 19 of 23
autoMick
in reply to: autoMick

I thought it was curious in my method above that it was possible to "add contours" to the surface, that weren't actually isobaths, but just splines connecting areas of different elevations. If you look at the picture attached - the white lines are the "contours" that were used to create the surface, but the colours show the true elevation ranges and are consistent with the original cross sections. 

 

It seems the "add contours" function is more a way to allow the adding of smoothed lines - which "add lines" seems to have a problem with. Is this correct? I imagine this could be misleading if someone imports contours that are for some reason incorrect.

 

Cheers

 

- Mick

Civil3d user in Australia since 2012.
Message 20 of 23
Yami72
in reply to: autoMick

You have done a good job Mick. C3D, suite programs and different extensions really has a lot of possibilties and usually only some of them are in use. Waiting for a day when I can say: "Computer, make a surface model of this river" 🙂

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