Topography

[7gdi]

I'm looking for ideas on how to model a 20+/- acre building lot that has hills/valleys. I've attached a copy of the site plan.

Thanks for any help or suggestions you might have.

[jameswillmott]

What I normally do is this.

Import the file to the correct scale as a background image in Modeler.

Trace the contours with a series of points at the appropriate height.

Join each line of contours with quad strips, inserting extra points if I have too few, and using tris where I need to step down points.

Once I'm finished I'll have an all quad/tri model which I can subpatch to smooth it out.

Sometimes I'll use that model to create a heightmap which I can draw on to edit and I'll use that map to displace a subdivided plane to give me a regular grid that follows the contours, depending on how I need to use the model.

[prospector]

Yea, same way here...splines

[Exception]

If its a complex map what I usually do is scan it in, use the smart fill tool in photoshop to make a gradient from dark to light and then apply this map as a displacement in layout.
Other ways are to scan it in and convert to live trace in illustrator, filling in the areas in between with live paint, export as an old illustrator file, open in modeler and apply the heights too each polygon string with set value, then triple and mergetrigonsX and subpatch.

other suggested ideas are also good.

[jameswillmott]

Exception, would you care to elaborate on your technique, the smartfill one?

[bjornkn]

I would start by drawing on top of one of the contours, quite coarse, and then close it to a poly with a single corner point.
Then I would select the contour points or edges and use the extender Plus tool, combined with the move and drag tool to drag points around to fit the contours. Finally either move all selected points down (or up) the correct distance.
Repeat extending/dragging/moving up/down as needed.
Finally delete the first, flat poly and continue adding contours from that first contour in the other direction.
Fast and flexible, and it allows you to add all the detail you want, where you want it.
Instead of using the map as a background image I would apply it as a planar mapped texture, with the correct size, to help when modelling.

[tommymamn]

I have been looking into this as well as a solution for a rendering I have coming up. I have always only done flat landscapes and this will be my first using a topo. I have looked at using displacement maps, but I have yet to create a good displacement map using photoshop. If anyone knows of any good tuts out there I would appreciate a link to it :)

I have attached the image of the contours for you to see.

Tom

[Exception]

Of course Accutrans converts CAd countour lines to a 3d model quite well...

[archijam]

My topo example for the day (coincidentally made 1 hour ago, hence the screens) -

Image 1: Took lines from cad, tidied and filled and cut out in illustrator (15mins - can do a huge area faster than in most 3D apps), imported to modeler.

Image 2: Assigned heights to areas for legibility (5mins).

Image 3: Selected contours and above, shifted vertically. Note you don't need to select by points if you merge your contour objects, you can very quickly more them progressively to the correct height. I exagerate the height, then scale it down as a final step, it avoids errors, and is easy in LW (10mins +).

Image 4: Brought in paths and drilled onto surface ... etc. etc. (10 mins .. had to do a surface at a time for the more complicated paths ...)

You will notice that this method a) works well with repetitive, 'offset' topography, and b) always needs some tidy up work (see welds across planes in middle of image). It is accurate enough for my needs...

j.

[Exception]

James, once you have the contours in illustrator, why not save them to cad, offset them there, pump it through accutrans, and be done with it?

With what you're doing you're likely to get highly nonplanar polygons, which will come to bite you in the soft cushioned rear end eventually...

[bjornkn]

So if you have contour lines in 3D, saved as dwg, will Accutrans then automatically "skin" the contour lines into a mesh, like you can do in SketchUp? In SketchUp there is often a lot of cleanup to be done though..

[archijam]

DEFinately non planar polys. But works for me.

I have had problems with the accutrans models if the topography is not steep .. maybe there is a workaround I don't know about ..

j.

[tommymamn]

Here's how mine turned out using accutrans...

Tom

[archijam]

THAT's what I'm talking about. The steppy-steppyness. Any ideas? Recently I just 'draped' over a nurbs surface in Rhino 3D to smother them out ...

j.

[MicroMouse]

How does AccuTrans create a DEM landscape from contour lines?

A DEM landscape consists only of elevations sampled at regular intervals in the north - south and east - west directions. Everything else needed to display the landscape on the screen or to save as a mesh to a file is calculated on the fly.

The first step is to specify the sample distance between the elevations. Usually this sample distance should be smaller than the sample distance wanted in the final 3D polygon mesh.

Using the sample distance a flat mesh is created and positioned above the contour lines. The wires in the mesh are lowered until they touch the contour lines. Very few vertices from the mesh will actually hit a contour line. The smaller the sample spacing the more vertices will hit contour lines or at least be closer to contour lines.

Where the vertex of the mesh hits a contour line the elevation is known. For all the other vertices, the elevations have to be calculated.

The north - south wire and east - west wire are followed from each vertex back to where the contour lines cut the wires. From these four elevations an elevation is calculated for the vertex in question. This algorithm needs improvement. The algorithms used by GIS map makers such as the USGS are more elegant than the one in AccuTrans.

Besides using smaller sample distances, extra contour lines could be added so that the calculation routines have more data to work with.

Even with smaller sample distances the algorithm does not have a smoothing calculation to give the same effect as draping a NURBS surface over the landscape.

I make contour lines for testing off of USGS DEMs so I get better results on conversions. If you want Tommymamm, you could email your contour lines to micromouse@accesscomm.ca so I can see what you are working with.

Wayne

[archijam]

Thanks for the explanation Wayne. I use Accutrans often, and for many situations the result is perfect. As you say it entirely depends on the data.

Since alot of my models are in switzerland, and the swiss are obsessed with topography, it works often very well .. Do you have plans for the DEM part of Accutrans?

j.

[bjornkn]

Another tool which might be helpful for making topography meshes is SimuTerra. It's 100$/200$ though. http://www.compuneering.com/

[tommymamn]

Wayne,

Here is the dxf file I am using. I pulled these off of a surveyors dwg file. I am posting it here in case anyone else wants to play around with it. Thanks for having a look. :)

Tom

[MicroMouse]

I have some ideas for the DEM module but no plans on when I might actually do them.

Wayne

[MicroMouse]

When converting the contour lines to a DEM landscape, I used a spacing of 5.0 units.

Landscapes are rectangular in shape. The contour lines do not cover a rectangular area so AccuTrans made a guess to fill in the area outside of the contour lines. You could add contour lines to improve the conversion in these areas.

I used the "DEM -> Smooth Cliffs" menu command twice to erode the steep cliffs.

I clicked on the "region" button to make a non destructive region from the landscape. There are polygons hanging down on the east and north edges of the landscape. I clicked the "E" button and then clicked the left mouse button with the cursor near the east edge of the landscape to cut off that area. I clicked the "N" button and did the same thing for the north edge.

I used the "DEM -> Convert to 3D (less water)" menu command instead of saving to a file just to save the step of reading the file back in. I converted using every vertex (step = 1)

I used the "File -> Add new file" menu command and read the contours back in so they would be superimposed on the polygon mesh.

I used the "Tools -> Erase textures on all layers" menu command as I didn't want the UV coordinates.

I have the "Viewer -> cull back faces" menu item not checked to have double sided rendering.

Rotate and zoom in on the mesh to see how the contour lines fit the landscape. For the landscape to fit the contours better a smaller sample interval will be needed.

Select "Display -> smooth shading" menu command.

Use the "Tools -> Calculate smoothing normals" menu command to calculate vertex normals for smooth rendering.

The LWO file wouldn't upload for some reason.

Wayne

[Exception]

Use the "Tools -> Calculate smoothing normals" menu command to calculate vertex normals for smooth rendering.


If only LW would support those :)

[MicroMouse]

I know nothing about the normal maps that Lightwave uses and have wondered if the vertex normals could be stored to normal maps.

Wayne