User Guide > Quickstart  

Modeling

 

Part One: Modeling the Rocket Fuselage
Part Two: Modeling the Fins
Part Three: Modeling the Moonscape
Part Four: Setting up the Objects


Part One: Modeling the Rocket Fuselage



1. Clear the Scene

Select File > New to clear the scene. When Houdini first launches, objects, cameras and lights are in place. For this lesson you want to make sure that you start from scratch and build these elements yourself. Creating a new file always clears the scene of any existing objects.

The Houdini desktop is made up of panes that each contain different kinds of information. There should be three panes open for you to work with:

  • The Viewer pane is where you see the results of your work and interactively manipulate its shape and form.
  • The Network pane provides a place for building up hierarchical and procedural networks which form the structure of your scene.
  • The Parameter pane gives you access to the details. Here you can set the parameters that define your work.

Understanding what each different pane type can do for you will help you be successful with Houdini.


2. Create a New Geometry Object

Place the pointer within the Viewer pane and press the tab key. Begin typing the word geometry on the keyboard. Houdini will narrow down your choices as you type. Once the options have been narrowed down to geometry press Enter.

A new piece of geometry will appear in the Viewer pane. It is represented by a default piece of geometry that will be replaced by your rocket model over the next few steps. In the Network pane you will find a geometry operator tile that can be used for selecting and organizing this element of your scene while the Parameter pane gives you access to transformation parameters that you will work with later.


3. Work with the Viewing tools

Before proceeding it is a good time to become familiar with navigating around the Viewer pane. The viewer pane is set up as a perspective view by default. You can navigate in this pane using the View tool. The View tool can be quickly accessed using the Spacebar to temporarily invoke viewing orthe Esc key which removes you from your current operation . Here are some examples using the Spacebar hotkey:

Spacebar - LMB to Tumble the view.
Spacebar - MMB to Dolly In and Out of the scene
Spacebar - RMB to Pan the view

Spacebar - Alt - MMB to Zoom In and Out of the scene
Spacebar - Ctl - MMB to the right to Zoom In
Spacebar - Ctl - MMB to the left to Zoom Out
Spacebar - Ctl - LMB to Rotate the view

Spacebar - h to Home the view.

Spend some time getting used to tumbling and adjusting the view. As you work through the lessons, be sure to use these view controls to help set up the right view for your work. Later you will learn how to change the view to an orthographic view.

4. Go to the Geometry Level

With the geometry object selected press i to go into the object. Objects act as containers for geometry and going inside provides you with a whole new working context. The geometry level is where you will define the shape of your object using surface operators known as SOPS.

You will notice that although the geometry has not changed, your pane has turned a different colour to indicate that you have entered Modeling mode. In the Type menu, you can see the word SOP which indicates that you are working with geometry.

5. Clear the Object

RMB-click on the default cube (but not the red handle) and select Delete from the pop-up menu. This empties your object so that you can add new surface operators. You can RMB-click on any object to get a context sensitive menu that provides you with some options.

Note: If you RMB-click on the red handle then you will get a totally different pop-up menu that offers a different set of options. Houdini's context sensitive nature will seem to slow down you down initially but very soon you will find yourself more productive because important options are always at your fingertips.

You can also clear the object by selecting Operator > Clear Current Object (New) from the Viewer pane menu.

6. Create a Tube Operator

Press the tab key again. You now have a new set of tools that work at the Houdini's geometry (SOP) level. You can now go to Generators and choose tube or start typing the word tube until Houdini recognizes it as the operation you desire.

7. Change the Primitive Type

At the top of the Viewer pane is the Operation Controls bar where you can change the Primitive Type to NURBS. This area contains commonly used attributes for the active operator. You could also make this change using the Parameter pane.

8. Edit the Tube's shape

The tube appears in the Viewer pane with a set of red handles. Most operators have handles which allow for interactive editing of key parameters. The handles as described below can be used to reshape the tube.

Now go to the Parameter pane. Some of these parameters match the handles displayed in the Viewer pane while others are unique to the Parameter pane. Parameters can be numbers, expressions, or options chosen from a menu.

You can change the radius and height values using the Parameter pane. Either enter the values directly or click drag on any field with your MMB to call up a Value grid. The grid lets you drag left or right to adjust the parameter value. The increments of the value change are determined by the particular square you start dragging from.

Set the values using either the handles or the Parameter pane so that your tube has a height of 2 and a top radius of 0.45 and a bottom radius of 0.35.

9. Add the Nose Cone

To add a cone to the tip of the fuselage and an exhaust to its base, you will use a cap operator that contains several attributes suitable for shaping the ends of the tube.

In the Viewer pane, press tab > Cap. The blue help text along the top of the Houdini window prompts you to select some geometry. Since the tube is already selected, RMB-click to confirm the selection. This puts a flat cap on the top and bottom of the tube.

In the parameter pane and set the top cap values as follows:

First U Cap to End Cap Rounded;
Divisions to 5;
Scale to 2.5,

Note: If youe MMB-drag in the Scale edit field, you can watch the nose of the rocket grow interactively in the viewer pane.

10. Add the Exhaust

In the parameter pane, set the bottom cap values to create the exhaust area. A negative value reverses the shape of the cap.

Last U Cap to End Cap Rounded;
Scale to -0.5.

11. Go back and edit the Tube

Tumble in shaded mode to view the final surface. Notice how the cap isoparm lines do not transition smoothly. This is because of the geometry settings found in the tube operator. Since the look of the final fuselage geometry is the result of the tube operator and the cap operator working in sequence it is possible to go back and edit the tube to affect the final result.

In the network pane, click on the tube operator. In the Parameter pane, click on the Detail tab and set the following:

Rows to 4;
V Order to 4.

The V order of the original tube used a degree that was best suited for straight edges. Once the cap was added, a higher order was needed with more detail.

12. Save your work

From the File menu select Save As... Name your file and click save it in your home directory.

Part Two: Modeling the Rocket Fins

To add detail to the Rocket, you will create fins around the perimeter of the fuselage. Rather than creating new objects, this new geometry will be built within the same geometry network then merged with the fuselage to create the final Rocket.

1. Go to a Right View

Move your cursor over the Viewer pane and press spacebar - t to display four views including the perspective view and three orthographic views. Move your cursor over the right view and again press spacebar - t.

Choose Wireframe from the Shading mode menu found at the bottom of the Viewer pane. If you don’t see this menu, click on the thin stowbar to reveal the View controls. You can also press w to change to wireframe mode.

2. Draw a Curve

With the cursor in the Viewer pane, press tab > Curve. The cursor changes to a small crosshair, and the blue text at the bottom of the Houdini window prompts you to, ‘Left-click to add points, then right-click to complete.’

LMB-click four times, to draw the curve. RMB-click once to complete the drawing.
Along the top of the Viewport, make sure the Primitive Type is set to Polygon, the Method is set to CVs, and the Closed option is checked. These parameters could also be set in the Parameter pane and could have been chosen before drawing the curve.

3. Extruding the Curve

Press spacebar-t once to go to a four view layout then move over the Perspective view and press spacebar-t again to expand this view. With the mouse in the Viewer pane, press tab > Extrude. Since the curve is already selected, RMB-click to accept. Next RMB-click again when prompted for a cross section. The shape is extruded by a value of 1. You don’t need the extrusion to be so deep.

Click in the viewport with your middle mouse button to call up a default Value Grid. Move to one of the unit grids and click-drag to change the value to 0.05. This will take one edit using the 0.1 grid square and then another in the 0.01 grid square. The value grid has been assigned to the Depth value of the extrusion and lets you change its value without clicking on the attribute in the Parameter pane.

4. Move the Fin

Press spacebar-t to see a four view layout. In the top view, use spacebar and your viewport controls to pan and zoom into the views to focus your view on the fin.

With the mouse in the Viewer pane, press tab > Transform. Click on the Select Whole Geometry button in the selector controls bar then click on the fin to select all of its parts. RMB-click to accept. A transformation handle appears to allow you to transform your object. Click in on the X axis handle to constrain along this direction and use the top view to help you centre the fin on the Z axis line. In the end make sure that the X translate value is set to -0.025 in the Parameter pane.

5. Set Display and Template Flags

In the Network pane, zoom in to see the cap1 tile and the new xform tile. The display of these operators in the Viewer pane is governed by the flag settings on each tile. For instance the xform1 operator has its Display flag set which makes it visible and selectable. This operator's handles are also visible in the Viewer pane. The cap1 operator has its Footprint flag set which also makes it visible and selectable.

Press u to go up to the Object level. You will see only the fins. This is because only the operator with the Display flag set is promoted to the object level. Later you will merge the different parts of the rocket so that everything is promoted.

Press i to go back in. On the cap1 operator tile, click on the footprint flag to turn it off then on the template flag to turn it on. Now this geometry is visible in wireframe but is not selectable.

Note: You can only have one operator's Display flag set within a single object while you can shift-click on footprint and template flags belonging to any number of operators.

6. Taper the Fin

Press tab > Transform. Press 1 to change your selection type to points and in a right view, select all the points on the left edge of the fin. RMB-click to accept. This brings up a transformation handle. Press e to display the scale handle then in a top view click-drag on the X axis line (not the arrow) to drag along that axis alone. Scale the points out until the fin is larger where it touches the rocket.

7. Create More Fins

In the Viewer pane, press tab > Copy. Notice the text at the bottom of your workspace informs you that the Copy Operation wants you to select the geometry to copy – the fin is still selected (i.e. yellow), therefore RMB-click to accept. You are then asked if you want a template, so RMB-click a second time to say No.

The fin is shown with handles for positioning the copies and the Number of Copies is set to 1. Before making new copies, you will set up an expression to link the number of copies to the rotation of the fin around the fuselage. In the Parameter pane, go to the Rotation-Y parameter and type in the Expression: 360/$NCY

This expression uses the variable $NCY (number of copies) as part of an expression that drives the rotation around the Y axis. This makes it possible to interactively change the number of copies and the resulting rotation angles will be evenly spaced. You therefore have the flexibility to change this value later.

Now use the slider to change the Number of Copies parameter. Watch what happens to the number of fins and how they space themselves around the base perimeter. Because of the expression entered in the Rotation field, Houdini spaces these copies out equally as you change the number of copies. When you finish, set the Number of Copies to 6.

8. Move the Spaceship to Ground level

Click on the footprint flag Press tab > Transform. Press a to select everything. The fins and the footprinted rocket are selected. RMB-click to accept. Click-drag on the transform handle to lift the rocket until the base of the fins sits on the ground plane.

In the Network pane, you will see that a merge SOP has been added before the xform SOP. Now all the geometry can be displayed together and promoted to the Object level. Press u to go up and see the whole rocket at the object level.

9. Go back and Bevel the Fins

Upon review the Rocket fins are too hard edged and require softening at the edges. To do this you will go back up the object's history and add new operators into the procedural network of the rocket. This ability to insert new steps into a network's procedural history is an important part of working with Houdini.

In the Network pane, check the Display flag on the second xform SOP that proceeds the copy SOP. To bevel this you will need to fuse the corner points of the extrusion then apply the bevel. Press tab > fuse. Press 1 to change your selection to points then press a to select all the points. RMB-click to accept. This adds a fuse operator inbetween the xform SOP and the copy SOP.

Press tab > PolyBevel. Press 2 to change your selection to edges then click-drag a bounding box around all the edges except those closest to the rocket body. RMB-click to accept. In the Parameter pane, select Absolute then set the Absolute Inset to 0.015. This provides a bit of an edge to the fin that will work well when the rocket is rendered later.

10. Go to Object Level

When you are finished, set the Display flag for the last xform SOP in the chain then press u to go back up to the Object level. Now all of your three panes are focused on objects and the Rocket is shown sitting at the origin. In the Network pane, click on the geo1 object name and change it to rocket.

Part Three: Creating a Moonscape

The rocket was built using a series of procedures that were merged into a final piece of geometry. To create a moonscape, you will begin manipulating points on a surface then sculpt the same surface using a paint-based interface.

1. Create a New Geometry Object

In the Viewer pane, press tab > Geometry then RMB-click to accept the new object without parenting it to another object. The new object is placed in the scene as another default cube. Rename it moonscape.

With the moonscape object selected in the Network pane, press i to go down into this object's geometry level. Select and delete the file1 operator so that you can begin building the surface of the moon.

Make sure the See one/all objects button is turned off to make sure the Rocket is hidden. This button makes it possible to work with other objects visible or hidden depending on how you want to work. For now, you don’t need to see the rocket to create the moonscape. Later you can turn it back on to preview the whole scene.

2. Create a Plane

In the Viewer pane press, tab > Grid. This places a new grid surface in your scene. Tumble in the Perspective view to see the grid from an angle. In the Parameter pane, set the following:

Size to 5, 5;
Rows to 30;
Columns to 30.

3. Edit Points on a Surface

Click on the stowbar at the right edge of the Viewport to bring up the Display options. Click on the points button to make sure that the surface points are visible as you work. In the Viewer pane press tab > Edit. On the left side of the Viewport make sure the Selector and Manipulator controls are visible and click on the points button. By default they will all be highlighted. It is important to note that the Selector stowbar found on the left controls what you select while the stowbar on the right controls what you see.

Make sure that the Select Whole Geometry button has been turned off so that you can focus on individual points then click away from the grid to deselect the points. Now pick four or five points at various points around the perimeter of the grid. Use the Shift key to make multiple point selections. RMB-click to start editing. If all points are selected with one click then you have not yet turned off the Select Whole Geometry button.

Click-drag up on the vertical transform handle to drag the points along the Y axis. This moves the points up to create small peaks. The results appear a bit harsh and could use some softening.

4. Soften the Edited Points

Click drag with your MMB to adjust the Soft Radius of the Edit’s selection. This creates a drop off for the resulting move. You could also adjust the Soft Radius slider at the top of the Viewer pane to achieve the same results.

5. Sculpt the Surface

Another way of reshaping the surface is Houdini’s Sculpt operation which uses a paint interface to push and pull the surface like a piece of clay. In the Viewer pane, press tab > Sculpt. Press a to select all the points then RMB-click to start sculpting. You may want to turn off Point display so that you can focus on the surface.

Your cursor changes to show a circle with a line pointing up from its centre. The circle shows the brush radius and the line shows the normal vector of the sculpt action. In the Parameter pane, set the following:

FD (LMB displacement) to 0.1;

Next, click on the Brush tab and set the following:

Radius to 0.4;
Opacity to 0.25.

You can adjust any of these settings between brush strokes as you sculpt. Click drag up on the surface of the grid to begin sculpting. Use your LMB to pull the surface and MMB to push the surface in. Leave the centre of the grid flat while building up the outer edge. This will create a crater for the ship to take off from.

5. Add More Detail

To further define the moonscape surface, you will apply a Fractal operation that will give an overall displacement to the grid. Press tab > Fractal then press a to select all the geometry. RMB-click to apply the fractal to the selected surface. The initial results are not ideal and you will need to adjust some parameters. Change the following in the Parameter pane:

Divisions to 1;
Scale to 0.025.

Reducing the divisions simplifies the surface and the scale adjusts the size of the displacement to suit the grid. This operation adds nice detail to the surface. Save your work.

Part Four: Setting Up the Objects

You have now experienced the Houdini workflow of creating geometry at the Modelling level (SOP). The creation of SOP networks creates models that define the shape of the objects in your scene. You will now return to the object level to position the objects in space. As you work with Houdini you will often switch back and forth between these two worlds.

1. Scale the Moonscape

Press the u key to go up from editing the moonscape’s shape to the object level. This hotkey is the same as going to the Type menu, and selecting Objects. Now you are looking at the two objects overlapping in space. Turn off the point display.

Press tab > Transform. Click on the moonscape then RMB-click to begin transforming. Press the e key to call up the scale handles. Scale the moonscape by about 10 times in all three directions. Use your view controls (W + [, ], or \) to zoom out from the rocket. Now the two pieces of geometry are working together.

2. Add a Camera Object

To view your objects for rendering, you will need a camera. This object type will let you look at your scene and frame the view much like a cinematographer does in a live action movie. In the Viewer pane, press tab > Camera. RMB-click to add the camera to the scene.

Use the camera handles to move the camera's eyepoint to the rim of the crater.

Select cam1 from the Camera list at the bottom of the Viewport. The rocket is probably not visible because the camera is not pointed in the right direction. Click on the Lock Camera to View button at the bottom of the Viewport next to the Camera list. This will let you use your Viewport controls to alter the camera’s position.

Use your Viewport controls (W + [, ], or \) to aim the camera at the rocket. This gives you a good starting view for your camera.
Turn the Lock Camera to View button at the bottom of the Viewport of so that your camera and the Viewport controls work separately. Save your work.

3. Add a Light Object