Creating swales on contour within a DTM

[J. Wallace]

Hi Everyone

I have a unique challenge which I thought I would post here. I have a site model of a 24 acre farm which I'm applying a permaculture design to.

One of the elements I need to add and thus effect the model are swales (see attached for side view). These are placed on contour (level) and in this case I would excavate a 3.5' wide by 1' deep swale and place the material downhill creating a mound. So the question is how do I create an object which will give my site model this look or effect? It needs to remove a channel and add down slope.

I very much appreciate any ideas, I'm certain this can easily be accomplished if you know how...

[Dillon]

If you have the DTM and you can draw the proposed contours, you should be able to get the model to show what you want. You'll need the contours to show both the dip and the mound.

I can't think of any automated way to do it.

[J. Wallace]

Thanks Dillon

I was hoping to use an extrude of some other shape as a form or template that would work as a site modifier to speed this process up. It will take some doing to place stake objects all along a swale and mound.

[CipesDesign]

You might try a series of Stake Objects (or 3d Loci), set to the correct elevations. Yes there will be some serious brain engagement required, but it just might work.

I'm thinking if you start off with all the points at the Site Model surface, then all you need is to lower each one by the same amount.

Of course the area needs to surrounded by a Grade Limits object...

Warning: Untested methodology. Please Save As before proceeding!

[Benson Shaw]

Another thing to try. Test in a test DTM, not your project file. It's more or less what Dillon suggested, and does not involve stakes. My test is a continuous ditch all the way around a hill.

Draw new contours representing the ditch bottom and spoil pile top and use these as either additional/replacement contours (#1 below), or as site modifiers ( #2 below - some hurdles to jump for this one). For example, On a new layer, draw the bottom of the ditch and top of spoil pile (draw in 2d>Convert to NURBS>raise to z value). This leads to V shaped objects. Additional contours at proper z can model the rounded shapes. Here are a couple processes.

Either:

1. Copy the new contours>Switch to DTM layer> Edit DTM (right click)>choose Edit Site Model Source Data>Paste in Place the new contours. Delete any overlapping original contours. Exit and update the DTM. Should give a ditch and spoil with steep sides. Will not make cut fill calcs because Vectorworks sees this as existing.

2. On the new layer, draw (2d) the ditch bottom and the spoil pile top.

Convert to NURBS> raise the z, Assign these to the Site-DTM-Modifier class.

Switch to DTM layer, update the proposed. Unfortunately, in my test anyway, the bottom of the ditch eliminates effect of all the uphill contours, leaving you with a flat surface. To get the top of the mountain back, to to the original contours, select all the contours above the ditch, copy them and paste them into the new layer. Reassign these contours to the Site-DTM-Modifier class. Update the DTM. Don't know what this does to Cut/Fill.

-B

[J. Wallace]

Thanks for all the feedback guys. I was playing with the file this morning and came up with this...

The swales are on contour ( or level, flat) which makes this a whole lot easier. I made a polyline which I felt would represent the bottom of the swale (and was following contour), then copied the same shape and converted both to site modifers (pads). Assigned elevations 2' below existing for the swale and 2' above for the mound. The grade limits seem to naturally create a smooth transition. I'm happy, and it was not difficult.

Benson I first started with NURBS object and changed this approach as I'm not that familiar with the behaviors of these. This is virtually the same approach just different objects. Thanks it works well.

[CipesDesign]

Jamie, that worked well! You're lucky the swale was level. That made it much easier than I had imagined it to be ;-)

[Benson Shaw]

Good work, Jamie!

I was trying to describe a moat all the way around a hill. Your swale is not a moat! Misinterpreted your needs. Sorry. The Pads in your drawing can be easily tilted via the OIP if you need a deep end or a drain direction.

FYI - NURBS curves:

A. Sometimes used (by me) to limit the number of vertices in site model source data in order to improve update times and keep file size down a bit. This may be a futile goal. One strategy I apply is to start with contours drawn as 2d splines>convert to NURBS>Convert the NURBS to 3d Polys. This extra step reduces vertex count in each source contour by 80% or more. eg an 8 point, closed spline yields a 17 point NURBS which converts to a 110 point 3d Poly. The same 8 point 2d poly converts directly to a 3d poly with 2049 vertices. Your mileage may vary. Sharper curves = more points in the 3d poly.

I also save my 2d splines on their own layer. Easiest to work with if contours need edit.

B. NURBS curves cannot be used as the initial site data. Vectorworks only accepts 3d polys and 3d loci for that. But, NURBS curves can be used directly as some site modifiers.

-B

[J. Wallace]

Thank you Benson and Peter...Benson, your notes regarding NURBS curves and how you use them are very helpful...thanks. I noticed my file is lagging a bit, when I zoomed in on a contour you can see many unnecessary vertices which explain the slow down. I may build a new model using your suggested methods.