ShaRP User Documentation

A (somewhat) Quick how-to for shape deformation in ShaRP:

1. Open a VRML or OBJ file.

2. Right click on the filename which appears on the object list to the right

3. Select Actions -> Edit

4. A Menu will appear to enable the MRF model go to Deformation Control tab.

Select Activate MRF

5. Add data by

(i) drawing with the cone object which you can control using

Cntrl+Mouse Move / Clicks (see External Device – Interface – DesktopMouseInterface – 3DMode.SketchData for details)

(ii) loading a second point or mesh file and selecting that file from

the object list then selecting add MRF data source. This will add the selected object in its shown pose as data points for the MRF deformation.

6. MRF Interpolation has 4 controls at the moment and will be changing:

Deformation Tab:

MRF Interpolation Controls:

Control 1:

Scale (Point / Patch / Surface) controls the size of the deformation for

a single point, i.e., how much of the surface reacts to a given data

point. This is controlled via a slider. At "Point" setting each point

effects a single mesh vertex, at "Surface" setting each point influences

the entire surface.

Control 2:

Data force (Tiny / Medium / Large) controls the relative force of the

data and the surface. Surface interpolations are obtained by finding a

surface which both passes through the measured (or sketched) data points

and simultaneously satisfies the surface constraints whcih control the

form/shape of the surface, e.g., smoothness. A setting of "Tiny" will

make the surface satisfy only its "internal" constraints, i.e., it makes

the data force small relative to the internal surface forces. A setting

of "Large" will constrain the surface to pass through the data (at the

moment you must also make the third and fourth controls small for this

to occur but will be fixed soon). The internal constraints of the

surface are controlled via the third and fourth slider which enforce

different surface constraints (for details see below).

Surface Fitting Constraints :

Control 3:

Mean Field (Elastic / Flexible / Rigid) controls the allowable deviation

of the mesh from its "original" shape. For example, if you load a plane

to deform, the original shape is defined by the collection of vertex

positions when you loaded the plane. At "Elastic" this constraint is not

enforced. At "Rigid" the points are constrained to be close to their

original position making the surface more "Rigid" when data is introduced.

Note: After deforming a shape you may update the "original" shape to be

the current collection of vertex positions by selecting "Freeze Current

Shape" this will set the "original" shape to the collection of current

vertex positions.

Control 4:

The Curvature Smoothing control is a floating point slider at the moment. It constrains the allowable curvatures present in the interpolation. If this force is large, the surface is constrained to be smooth, i.e., the penalty requires that the curvature vary smoothly over the interpolated surface.

Another useful button is the "Reset to Frozen Shape" which will reset

the vertex positions to the positions specified on the "original" shape.

Which may be the loaded shape (if "Freeze Current Shape" function has

not been called) or the most recently "frozen" shape (if the "Freeze

Current Shape" function has been called).

Now that you have all of the controls for interpolation down, there is the final wrinkle of actually controlling WHEN and WHERE the surface is deforming.

Controlling WHEN the surface is deforming:

This is done by clicking on the "Deform MRF" button. When this is selected, some rather lengthy computations will begin followed by interpolation iterations and the surface will begin to deform. You can toggle the deformation "on/off" by re-selecting "Deform MRF".


Controlling WHERE the surface is deforming:

This is done by selecting some subset of the surface. There is a variety of selection methods available. Surface Selection may be performed from the "Surface Selection" tab for selecting large portions or all of a given surface. For more detailed selections involving smaller portions

of a surface, a manual selection interface is provided which is similar to the sketching interface.

Surface Selection Tab:

Whole surfaces or discrete surface patches specified as groups of triangles within the loaded file may be selected using the "Surface Selection" tab.

Item 1 : The Triangle Group List

A list of surface patches corresponding to discrete triangle groups is shown in a window with names "Group 0","Group 1","Group 2", etc.. The number of groups listed will be the number of distinct triangle groups in the loaded file and will vary depending on the type and internal structure of the loaded OBJ or VRML file. One may select any subset of the list by clicking on the group(s) of interest. To select more than one group you must hold down the Cntrl key while clicking on the groups of interest. Selected groups are then rendered as blue surfaces.

Item 2: Select All

This selects all the triangle groups (*shortly I will make this a hot-key Cntrl-A*).

Item 3: De-Select All

This clears the selection to be nothing.

Item 4: Invert Selection

When a subset of a triangle group has been selected, this will "invert" the selection by removing all of the selected vertices and subsequently selecting all vertices which were not previously selected. For example, say a triangle group has 5 vertices labeled {1,2,3,4,5}. We select {1,2,3} then invert the selection. The result will be the selection {4,5}.

Item 5: Select Connected Groups

This function will use the current selection as a seed to select all vertices which are connected to any of the selected vertices. Taking our example from above, say we select only vertex 3. Selecting this function will change our selection from {3} to {1,2,3,4,5} since the vertices {1,2,4,5} are connected to vertex {3} in the mesh.

External Device Interface

There is a generic interface which allows the user to interact with objects in 3D. This interface is compatible with a number of different devices which include the Polhemus ISOTRAK & FASTTRAK (and our custom adaptation of this device for sculpting), Immersion Corporation’s Microscribe 3D articulated 3D arm, and a standard desktop mouse. Since the latter of the 3 devices is by far the most common I will describe it’s interface analogies here and will leave the rest for another day.

Desktop Mouse Interface

The desktop mouse typically has 3 buttons referred to as the left, middle and right buttons. The ShaRP program reacts to the desktop mouse in 2 modes. These modes are mutually exclusive and completely change how the mouse is interpreted by the program. At the moment, there is no visual feedback defining the active mouse mode (this to be fixed). We will refer to the two modes as the "standard" mode and the "3D" mode.

Mouse Standard Mode

Typically the mouse is in standard mode, which allows the user to select menu options from the top bar, select objects such as points, meshes, and lighting from the left side of the screen and orient objects in the scene.

Orienting objects in the scene

To orient objects in the scene, the user must select the object(s) on the left portion of the screen. Selection of more than one object is accomplished by holding Cntrl while clicking on the objects of interest. Once, the objects have been selected the pose of the selected objects is controlled by clicking a button and dragging it, i.e., moving the mouse while the button is depressed, either up/down or left/right while in the 3D canvas (middle of the screen). The controls are interpreted as follows:

Left Mouse Button : Rotates the object(s) around the centroid of the first selected object. Movement left/right specifies clockwise/counter-clockwise rotation about the Y axis (the verticle axis). Movement up/down specifies clockwise/counter-clockwise rotation about the X axis (the horizontal axis).

Middle Mouse Button : Translates/Zooms object(s) by changing their depth (Z) position. Movement up/down specifies the object depth to be farther/closer to you.

Right Mouse Button : Translates objects by changing their (X,Y) position. Movement left/right specifies a positive or negative change in the X position of the objects. Movement up/down specifies a positive or negative change in the Y position of the objects.

Note that it can be easy to move objects off the screen, I would like to make a function to send them back to their original position when loaded but this is not present as of yet. Normally, the object may be "found" by moving it farther away, i.e., translating along the Z axis.

3D Mode for the Desktop Mouse

The 3D Mode for the mouse is enabled/disabled by holding down/releasing the Control key. One must ensure that the 3D canvas, i.e., the main screen of the program is selected and that the mouse is positioned over the 3D canvas when the Control button is pressed AND released.

NOTE: Sometimes drag operations will take the mouse outside of the window. In this case the window will not register the release of the Control key and you may get "stuck" in the 3D mode. To get out of this mode, select the 3D canvas with the mouse and tap the Control key several times.

When in 3D mode, the mouse controls a pink cone referred to as the
*tool* present in the scene. The position of this object is controlled in the same way that the object positions are controlled as detailed in the section "Orienting Objects in the Scene." For completeness this is:

Control+Left Mouse Button : The interpretation of this button depends upon the selected interface mode (see following section on 3D interface modes for details).

Control+Middle Mouse Button : Translates/Zooms the tool object by changing its depth (Z) position. Movement up/down specifies the tool depth to be farther/closer to you.

Control+Right Mouse Button : Translates the tool by changing its (X,Y) position. Movement left/right specifies a positive or negative change in the X position of the tool. Movement up/down specifies a positive or negative change in the Y position of the tool.

NOTE: The Cntrl key must be held down the entire time during these operations. When it is not held down, the mouse is in "standard" mode.

There is currently 3 possible modes. This document will describe two : "Sketch Data This is detailed in the following sec

3D Interface Modes

There are 3 possible interface modes which use the tool position in order to perform useful operations on objects in the 3D space. The modes may be changed by selecting the Remesh / HCI tab. At the top of this tab are the modes labeled :

1. Sketch Data

2. Add Attractor

3. Make Selections

The mode may be specified by clicking on one of these three labels. The purpose and interpretation of each mode is as follows:

Sketch Data

This mode allows the user to lay off points in 3D space. If the MRF model is enables (in Deformation Control) then the points are interpreted as data which serves to deform the MRF surface. Data points are placed at the tip of the cone tool and one may specify curves in the XY plane by holding the Cntrl key down, clicking the left mouse button over the 3D canvas, and dragging the mouse left/right and up/down. This is generically referred to in this document as "3D sketching."

Add Attractor

This allows one to place a single attractor (shown as a grey sphere) which is used in conjunction with the growth model from the "Growth Control" tab. *NOTE I will describe this later*.

Make Selections

This mode allows the user to select subsets of the surface. Surface selection is an important tool for deformation, shape editing, and shape growth and specifies the surface regions of interest for these different operations.

    When this mode is selected the tool changes from a cone into a semi-transparent sphere. One may vary the position of the sphere in the same way as that of the original tool and additionally may change the radius of the sphere by varying the value of the numeric slider (the slider could use some clarifying labels) immediately below the interface modes in the "Remesh/HCI Mode" tab. Regions are selected by moving the sphere to intersect the surface patch of interest (using the same technique used to move a tool) and subsequently clicking the left mouse button. When this occurs all points within the transparent sphere of the tool will be selected. One may select contiguous regions by holding the left mouse button down and dragging mouse (and correspondingly the sphere) around on the canvas which will continuously add points within the sphere to the list of selected points.