# Camera frustrum bounds for simulation

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Hello,

I am using Houdini 18.5 with the pyro sparse solver and simulating plane trails moving from point a to b.
When simulating first 100 frames it goes quite fast.. max 1 minute per frame but for the next 100 frames simtime is now almost 15 minutes per frame and I am only talking about 1 trail. Multiple will be added soon.

Problem is I actually don't need to simulate the areas where the camera does not see the trail. After 100 frames, over 50% of the trail is not even in the camera frustrum anymore. I was wondering if I can use some kind of dynamic bounds with the camera frustum. I only want it to process the data when seen by the camera. If the trail moves out of the camera frustrum it does not need to be simulated anymore. Not removing it after the simulation but while the simulation is necessairy to improve the speed.

Any hints?

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maybe it Helps

```// accum the frame range

int sf = detail(1, "startFrame");
int ef = detail(1, "endFrame");
int npts = npoints(1);
// range loop our points , cal the weight of there camera matrices!
for(int i=0; i< npts ; i++)
{
float mat[];
mat = point(1,"mats", i);
matrix mat44 = set(mat);
vector camP = @P * mat44;
camP = normalize(camP);

int condition1 = camP.x < -0.5 || camP.x > 0.5;
int condition2 = camP.y < -0.4 || camP.y > 0.3;
int condition3 = camP.z > 0;

int condition = condition1 || condition2 || condition3  ;
if(condition ) {
@accum += 0;
}
else{
@accum += 1;
}
}

@accum = @accum / npts;
@Cd = @accum;
if(@accum <= 0)
{
removepoint(geoself(),@ptnum);
}```

Python

```node = hou.pwd()
geo = node.geometry()

# Add code to modify contents of geo.
# Use drop down menu to select examples.

frameStart = node.parm("start").eval()
frameEnd = node.parm("end").eval()
fps = 24.0

# add detail attribute to save our frame range that is camera key range

# get camera node:
camNode = hou.node("/obj/cam1")

matrix_list = []      # this is our camera matrix here
for frame in range(frameStart,frameEnd+1,1):
time = float(frame)/ fps
camWorldMatrix = camNode.worldTransformAtTime(time).inverted()  # get camera at time!
camWorldMatrix = camWorldMatrix.asTuple()
matrix_list.append(camWorldMatrix)

# add a array attrib in every point, our point is our frame

for it in geo.iterPoints():
it.setAttribValue("mats", matrix_list[ptnum])```

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