## collisions detection

## Principle:

In dynamic animation this command allows to manage collisions between objects.
If yes dynamic is active and
if the objects are equipped with masses some effects
can be obtained (bouncing, sliding, friction, etc. ..)

It is necessary to activate collisions by
yes collision.

See for example `set_anc()`

function of file
demo1_collision.func.
## collision anc

### collision anc vol(id1)

Returns the **collision anc** property of volume **id1**.
### collision anc vol(id1)=id2

Change this property.

**Notes:**

the distance(id1,id2) is maintened in **[d1,d2]** by forces module **c**

With property collision follow followers are also
processed.
### collision follow vol(id1)

Returns the **collision follow** property of volume **id1**.
### collision follow vol(id1)=id2,id3,...

Change this property.

**Note:**

Any couple **idi,idj** are managed with force rota
in order to avoid collisions.
### collision limit vol(id1)

Returns the **collision anc coe** property of volume **id1**.
### collision limit vol(id1)=d1,d2,c

Change this property.

**Notes:**

the distance(id1,id2) is maintened in **[d1,d2]** by forces module **c**
(by default d1=d2=100 c=0.5).

to ovoide trembling set a viscosity < 0 to this force, for example:

`force vol(id0)=0,0,0,-.5;`

## collision ball

### collision ball vol(id1)

Returns the property **collision ball** of volume **id**.
### collision ball vol(id1)=x,y,z

Changes this property.

**Note:**

**vol (id)** is the root of an anchoring structure
(for example the pelvis of a body).

Defines a ball obstacle center **(x, y, z)** and radius(r).

Multiple collision balls on the same volume **id** can be defined by:
```
```

collision poi vol(id)=x1,y1,z1, x2,y2,z2, ...

collision radius vol(id)=r1,r2, ...;

## collision center

##

### collision center vol(id)

Returns property **collision center** of volume **id**.
### collision center vol(id)=x,y,z

Changes this property.

**Note**:

With property collision radius vol(id)=r, volume **id** rebonds
inside sphere center **(x,y,z)** and radius **r**, see also collision coe
and collision force
## collision coe

### collision coe vol(id)

Returns the **collision coe** property of volume **id**.
### collision coe vol(id)=reb,fric

Change this property.

**Notes:**

**reb**: coefficient of rebound changing the speed after the shock
(< 0: lie flat on the ground, > 0: unstick).

**fric**: coefficient of friction, if != 0.0 the rebound occures only if
(**module(speed) > fric** (25 default).
## collision collision

### collision collision vol(id)

Returns the **collision collision** property of volume **id**.
### collision collision vol(id)=id1,id2,...

Change this property.

**Note:**

**id1,id2,...**: are the identifiers of the volumes which react in case of collision
(all by default).
## collision force

### collision force vol(id)

Returns the **force** property of volume **id**.
### collision force vol(id)=f,c

Change this property.

**Note:**

**f**: modulates the reaction (0 by default).

**c**: transmission coefficient (0 by default).

**-1,.75** are good values.
## collision func

### collision func vol(id)

Returns the **collision func** property of volume **id**.
### collision func vol(id)="fff"

Change this property.

**Note:**

**fff** is the name of an anyflo function which will be executed each
**collision** of the anchored structure of root the volume **id**.

Such a function has one formal parameter **id**.
## collision normal

### collision normal vol(id)

Returns the **collision normal** property of volume **id**.
### collision normal vol(id)=nx,ny,nz

Change this property.

**Notes:**

**(nx,ny,nz)** is the normal to the plan through point colliisin poi vol(id) (0,-1,0 by default).
## collision poi

Allows an anchored structure to "walk" (eg body) on a floor.
### collision poi vol(id)

Returns the **collision poi** property of volume **id**.
### collision poi vol(id)=x,y,z

Change this property.

**Notes:**

**vol (id)** is the root of an anchoring structure (for example the
pelvis of a body).

Defines an horizontal obstacle plane passing through the point **(x, y, z)**, to change the orientation see
collision normal vol(id).

Multiple collision planes on the same volume **id** can be defined by:
```
```

collision coe vol(id)=reb1,fri1,reac1, reb2,fri2,reac2...;

collision normal vol(id)=nx1,ny1,nz1, nx2,ny2,nz2, ...;

collision poi vol(id)=x1,y1,z1, x2,y2,z2, ...;

**Example:**
```
```

collision coe vol(id)=1,10,.25;

collision normal vol(id)=0,-1,0;
collision poi vol(id)=0,0,0;

## collision radius

### collisionradius vol(id1)

Returns the property **collision radius** of volume **id**.
### collision radius vol(id1)=r

Changes this property.

**Note:**

if volume **(id)** has a property collision ball, **r** is
the radius of the ball.

if volume **id** has a property center **r** is the radius of the sphere.
## collision sphere

### collision sphere vol(id)

Returns the property **collision sphere** of volume **id**
type particle.
### collision sphere vol(id)=x,y,z,r1,r2,c

Changes this property.

**Note:**

if yes collision,
yes dynamic and
yes particle
are active, the points of volume **id** will rebound, with a coefficient **c** (1.0 default), on the sphere
center **(x,y,z)** and radius **r1**

The rebound direction varie form 0 (at **r2**) to the symetric to the normal, so simulating a fluid.

**r1, r2 > 0**: outside.

**r1, r2 < 0**: intside.

**r1=r2**: non compressible fluid.
## collision vol

### collision vol(id)

Returns information collision volume **id**:

**flag,v,s,x0,y0,z0,x,y,z**:

**flag** = 1: new collision.

**flag** = 2: same collision.

**flag** = 0: no collision.

**v** = collision volume number, **s** = collision vertex number.

**x0,y0,z0** = old collision position.

**x,y,z** = new collision position.

**Notes:**

Allows determine the point of contact:

```
c=collision vol(f);
```

if(c!=NIL)

{

vc=c[1];sc=c[2];p=poi(sc)matrix vol(vc);

...

}

## collision vol near

### collision vol(id)near

Treats volumes **id** collisions between them with the same options as
que **collision vol vol**.
## collision vol vol

### collision vol(id1)vol(id2)

Treats volume **id1** collisions on the obstacle **id2**.

**Options:**

**ball**: only tests balls are activated (fast but is only suitable
for approximately spherical objects.

**box**: only test boxes are activated (slower, suitable for objects
which could determine bounding boxes.

**segment**: suitable for objects wired (ie reduced to a single
facet of connected points).

**fac**: slower but suitable for any type of object, the default
(without option).

**dist(d)**: anticipated collision of **d**.

**coe(f,v_f,r,v_r,c)**: if yes dynamic is active and
if the objects are provided with masses:

**f,v_f** = rebound and viscosity force

**r,v_r** = rotation force and viscosity

**c** = radius multiplier with option ball

(0,0,0,0,1) by default, .1,-.01,.01,-.01 are good values
de bonnes valeurs).

**Examples:**

**ball ball**: objects and obstacles are approximately spherical.

**segment ball**: objects are wired obstacles are approximately spherical.

**segment segment**: objects and obstacles are wired.

**segment fac**: objects are wired , obstacles are arbitrary.

**etc..**
## See also: