TUTORIAL: Rendering Cityscapes with RailClone and Forest Pack (advanced)
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TUTORIAL: Rendering Cityscapes with RailClone and Forest Pack (advanced)

In a previous tutorial, we examined how to
use RailClone to create a single parametric building. In this tutorial, we’re going
to up the scale and share techniques to quickly create entire cities! Staring with a simple grid, we’ll demonstrate
how to populate a city with 3 types of building, each showcasing a different technique. We’ll
start with courtyard buildings, add towers that are automatically scaled and oriented
to fill and entire city block, and finally fill blocks with multiple mid-size commercial
buildings. All these techniques use RailClone, a procedural
modelling tool from iToo Software. In addition to useful layout tools, RailClone is able
to render enormous polygon counts, making it well suited for this kind of task. Don’t
worry if you don’t have RailClone, you can use the free version downloadable from iToo
Software’s website (itoosoft.com). This Lite edition limits you to 3 source building
models per RailClone object, apart from that all the other techniques shown in this tutorial
will work fine. To populate the city you can use existing
assets or model them yourself. In this tutorial, we’ll demonstrate using buildings from Evermotion’s
(evermotion.org) extensive collections. The courtyard houses come from collection AM172,
the skyscrapers and towers from AM181, and the mid-size commercial buildings from collection
AM181. We will also use low-poly cars from collection AM132 to fill the roads. If you
visit the Evermotion’s website, you can download a selection of free samples from
each collection to follow along with the exercises. Start by laying out the city using 3ds Max’s
built-in tools to create a closed spline for each city block. When designing the city there
are a couple of things to consider: Firstly the techniques in the tutorial work best with
rectilinear city blocks; secondly vertex types should be set to Corner for 90 degree bends,
these will be used by RailClone to add corners and are also useful to add zebra crossings
and other details at the intersections to the streets; thirdly, for gradual changes
in direction use Bezier, or Smooth vertex types but be aware that we won’t be deforming
geometry in this tutorial so there’s a limit on how curved splines can be before adjacent
buildings intersect. Once your city is created, it’s a good idea
to create a smaller collection of splines you can use to test out your procedural styles.
This will speed up the creation process because Forest Pack and RailClone won’t need to
perform complex calculations on the entire city grid. Create a couple of rectangles and
a straight spline and attach them so that they’re a single object. Next, merge your
chosen assets into the scene. In this example, we will use the free sample from Evermotion’s
AM172 collection of house models. RailClone does not automatically consolidate
materials and reassign IDs, so you will need to create a single Multi-Sub object material
that can be applied to all of the source geometry. To make this clear, the same single material
needs to be applied and work correctly on both the RailClone object and the individual
components. An easy way to consolidate materials is to attach the objects together into a single
mesh. By doing this, Max creates a multi-sub object material and reassigns IDs automatically.
You can then detach each object back into separate objects, centre and re-adjust the
pivots. Now we’re ready to create the first of the
three types of RailClone object we’ll study in detail for this tutorial. This one will
add buildings around the perimeter of a city block, and it’s particularly suited for
courtyard, townhouse and terrace style architecture. Create a new RailClone object and open the
Style Editor. Create an L1S generator and wire a new Spline node to the generator’s
Spline input. Use the Spline node to select the test spline we created in Step 2. Create
a new Segment node and disable Slice and Bend to make sure that full instancing is retained. To add all the buildings to the RailClone
graph, right click on the existing Segment node and select Clone Multiple. Select the
building objects and click OK. Each will be automatically loaded into a new segment with
the same settings as the original. Wire the Segments to a new Randomise node and wire
the Randomise node to the generator’s Default input. The buildings are centred on the spline.
To change this, wire a Transform node between the Random node and the Generator and use
it to change the Y-Alignment to Bottom. Wire an empty segment to the Corner input and set
the Generator’s Bevel Mode to None. Note: When using high-poly source geometry,
RailClone displays the objects as simple boxes to keep the viewports fast and interactive.
You can also choose to display the geometry as a points cloud. These settings can be edited
in the Display rollout. The way that RailClone distributes segments
to fit along the spline can be controlled using the Default options found in the Generator’s
Rules tab. In Tile mode, the segments are simply placed one after another along the
Spline and the final segment is sliced to fit. Because we have disabled slicing though,
the final segment will extend beyond the end of the spline which will cause problems with
buildings extending outside the block and crossing the pavements and roads. There are three other Default modes available:
Adaptive which subtly scales all the segments by the same value so that they fit the spline
exactly, Scale which stretches a single Segment the length of a spline section, or Count which
allows you specify a fixed number of Segments and then scales them to fit the available
space. Unfortunately these all require the segments to be exactly the same length on
the X-axis, which is not the case with our buildings. So none of these existing modes are appropriate,
luckily you can add others using the built-in macros. Set the mode to Tile and add a Scale
Final X Segment Macro from Macros>Transforms. Wire it between the Transform node and the
Generator. This macro will scale the final Segment before a corner or the end of the
array to fit the available space. The Minimum Last Object Size parameter is used to determine
the minimum size of the final building. If you increase this value you’ll get larger
final buildings, if you lower it you will get smaller buildings. Because the position of the building following
the corner does not take into consideration the depth of the buildings before the corner,
there are overlapping segments after the corners. To fix the problem, we need to add random
buildings to the corners in such a way that we can reliably predict their size. The randomise
node won’t work for this, instead wire the existing buildings to a new Selector node,
export the Index and wire it to a Random Number node. Set the Min value to 1 and the Max to
the number of buildings attached and set Generate On to X Spline Section. Wire a Transform node between the Random node
and the Generator and use it to change the Y-Alignment to Bottom. Now we need to control
how buildings are arranged at the corner. We want a single building to appear entirely
before the corner vertex, with an empty segment following the corner the same size as the
Y Dimension of the preceding building. To do this we wire a Compose operator to the
Corner. Wire the Transform node to the first input, wire an empty Segment to the second
input, then wire it to the 3rd input but this time via a Transform operator that we can
use to control its X Size. Export the X Fixed Size of the Transform node
and be sure to enable it in the parameters. Export The Y Size attribute from the Selector
operator and wire this to the X Fixed size input of the Transform node. The Y Size of
the randomly selected corner segment now controls a gap that follows the corner. To finish the
effect, wire the Selector Operator’s output to the End Segment input of the Scale Final
X Segment macro. This will allow the macro to take into account the size of the corner
segment when it calculates the size for the final segment. For all the styles in this tutorial, we will
add the ability to use the material ID assigned to a spline section to control whether or
not it generates geometry. To do this right-click on the generator and export Limit by ID and
Limit Material ID. Wire a new Numeric node to each of these inputs and change the type
of the first to Boolean, and the second to Integer. Using the parameters rollout you
are now able to control whether the Limit by ID function is enabled or disabled and
choose which ID value generates geometry. The style is now built. If you want to create
more variety you can now duplicate this RailClone object and swap the geometry referenced in
the Segment nodes to create different architectural styles for each block. Give each RailClone
object a different material ID so that you can easily manage how they are distributed
on the city grid. In our sample render we had 20 different courtyard styles, each with
its own corresponding material ID. In the next section of the tutorial we’ll add skyscrapers
that rotate and scale to fill an entire city block. After preparing the source geometry, as discussed
earlier, so that all assets share the same Multi-Sub Object material, create a new RailClone
object and open the Style editor. Create a 2D array then add a new Spline node and wire
it to the Clipping Spline input. Pick a spline from the scene. In the Generator’s settings,
enable Extend X/Y size to area so that the size if the array is automatically calculated
to fit the size of the base spline. Change For No Slice to Preserve. Add the buildings
by adding a new Segment, disabling Bend and Slice, and using the Add Multiple option to
import all the tower buildings. Wire all the building segments to a new Randomise
node and wire the Randomise node to the Default input. The buildings will be tiled inside
the spline area. We want exactly one building per spline area. We could use the Generator’s
Default>Scale mode, but this only works for the X-axis. Instead, we’ll use a macro
that allows you to scale on both axes. Wire a Scale to Array macro between the Random
node and the Generator and enable Scale to Array X and Y. Next, we want to rotate the
building to match the orientation of the spline. By default, the array’s rotation will match
that of the RailClone object. We want each array to rotate to match its sub-spline. To
do this, open the generator’s settings and change Auto-Align mode from None to Spline.
This mode calculates a direction vector based on the first and second vertex in a closed
spline and uses it to align the array. While you’re here you should also change Hierarchy
Checking to None to drastically speed up calculation times. Finally, export the Limit by Material
Id and Limit by ID values and wire them to Numeric nodes. The third technique combines the previous
two. We will automatically calculate the size and orientation of the array, but then scale
the final segments on the X and Y axis so that multiple buildings can fit neatly inside
a city block. To do this, Create a new RailClone object and open the Style Editor. Add an A2S
generator and turn on Extend X/Y size to Area, set Auto-Align to Spline and set Hierarchy
Checking to None. Attach a Spline node and pick the spline from the scene. Create a Segment
and disable Bend and Slice. Use Add Multiple to import the buildings. Wire all of the building segments to a new
Randomise node. Wire the Randomise node to a Transform node and add some padding so that
there’s a gap between the buildings. To ensure the buildings fit inside the spline,
we’ll scale the final building on the X and Y axis by adding two Macros. Wire a Scale
Final X Segment and Scale Y Segment macro in series between the Transform node and the
Generator’s Default input. These are the same macros we used for the Courtyard blocks.
Increase the Min Last Object Size parameter until you remove any ultra-thin buildings. To finish the style, once again we export
the Limit by Material ID and Limit by ID values and wire them to Numeric nodes. Set the Material
ID value to 22. You now will have 20 courtyard building variations on Material IDs 1 – 20,
Skyscrapers on Material ID 21, and finally offices and commercial buildings on material
ID 22. Using these numbers you can change the material IDs on your city grid to design
your layout. Alternatively, for the demo scene we used a script (included in the downloads)
to Randomise the IDs. Note: When you want to assign a spline to
multiple RailClone objects you can use a simple code snippet. Select the RailClone objects,
open the Maxscript Listener (F11) and type for obj in selection do obj.banode[1]=$SplineName
(where $SplineName is the name of the spline). Once you are happy with the layout of the
city, save the file and create a new Max scene. We will XRef the buildings into this scene
so we can continue to add details without having to wait during long save times. Clone
the city spline and extrude it to create a base for the building and add a plane the
size of the whole city. Translate the plane down on the Z axis the height of a pavement
to create the roads. The city grid spline can also be used to add cars to the streets. Note: Instead of modelling and texturing roads
you can use a simple plane to cover the entire area and use V-Ray Distance Textures to parametrically
add wear and tear based on the distance of the surface from the city block. Either RailClone or Forest Pack could be used
to add cars, but for this example we’ll use the former. Don’t forget though, that
your car models will need to be prepared so that they share a single Mult-Sub Object material
and none of the geometry should be grouped. Then, create a new RailClone object and add
car models to the graph in the same way as we did for the buildings. Wire them to a Randomise
operator, and add a Transform node to rotate the cars and add some Translation variation
if necessary. If you wire the Transform node to the Default
input, the cars will be bumper to bumper. To add some spaces, add a new Sequence operator
after the existing Transform node, then wire a brand new Transform node to the second input.
Wire a Null segment to the new Transform node, export its X Fixed Size and enable it from
the parameters. Wire a Random Number node to the X Fixed Size input and adjust the Min
and Max values to control the spacing. To make this style easier to edit from the
Modify panel, let’s export a few parameters. From the Random number node, export the Min
and Max values and attach new Numeric nodes set to Scene Units. From the Generator, export
Fillet Radius, Y Offset, and Z Offset. Wire new Numeric nodes to these too, all set to
Scene Units. Once you’re done, you can apply the style to the city grid and easily adjust
the parameters to position the cars and control the density from the modify panel. For multiple
lanes, simply duplicate this object and edit the Y Offset value. There are several other RailClone objects
in the final scene. Most of these are very simple and are included in the exercise files
so you can see how they’ve been created. For example, we used RailClone to add the
pavements, the street lights, road markings, pedestrian crossings, and even people walking
along the pavements. To make things easy to set up, all of these are driven by the same
set of city grid splines used to generate all of the buildings. Let’s take this even
further and use the same splines again to add trees to our city. We will use Forest Pack to add trees to the
streets. Create a new Forest Pack object by dragging an icon in the viewport. Open the
Modify Panel, go to the Distribution rollout, and change the mode to Path. Add the City
Grid to the Splines list and use the Spacing property to control the distance between trees.
In the Geometry rollout, add a tree from the library. If it’s too large you can resize
it using the Scale property. Back in the Distribution rollout, use the Y Offset value to move the
trees to the edge of the pavements. The courtyards look too empty so let’s add
trees to them too. Clone the city grid and delete the sub-splines that create the towers
and commercial buildings. Create a new Forest Pack object and add the spline to the Areas
List. In the Geometry rollout, add one or more trees from the library then go the Distribution
rollout, select a pattern and adjust the density. For both Forest Pack objects, enable Rotation
and Scale Randomisation and Enable Limit to Visibility and Auto Assign to Active View
from the Camera rollout to optimise the scene by removing items that are not visible in
the final render. To remove the trees from the edge of the city
block where they intersect with the buildings, go to the Areas Rollout and enable Density
Falloff. Edit the Falloff graph so that it’s stepped to create a hard cut off instead of
a gradual reduction in Density. You can then increase the Include value to remove trees
from the perimeter of the city block. To reduce the size of the trees you can use the Scale
falloff settings. This time though, don’t set the Minimum scale to 0 in the falloff
graph, 30 – 40% will look more realistic. Using these tricks and techniques we have
been able to generate hundreds of buildings, thousands of trees, streets full of cars and
people and many more small details to create a convincing 3D render. Best of all, once
you’ve set this up you can easily create cities for other projects just by changing
the base spline. You could even extend this by adding more RailClone items to the streets
to create street clutter such as road signs, traffic lights, bus shelters, bins advertising
hoarding and much more. Experiment, and have fun!


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