Delete points based on distance

andmotion

Hey Sebastian,

It's sound for me really complicated
What I would like to achieve is this :

Based on the distance between two object, remove points from the object_1 while the object_2 is close enough to the object_1.
Would that be possible in Xpresso and its point node?

Thanks again for your input.
Thanks,
Andrzej

andmotion

Hey zipit,

Thanks for your suggestions.
I am coming from vex Houdini so I can picture the code here how I can get this type of effect in Houdini I know it's not relevant to C4D but I am trying to make this simple effect in C4D.

In H it would be like this :

I have sphere as a obj_01, lets assume 100 points
I have one single point somewhere in obj space
I am taking the @P attributes of the points from obj_01 so I know now position of each point from obj_01
I am taking the @P attrib of the single point
Now when I know both vectors I can easily say this :
-- if the pos of ONE POINT is close enough POINTS from obj_01
delete those POINTS from the obj_01

Hope that make sense:)
I did never script in c4d so I can not post here any examples:(
Ta

s_bach

@andmotion The question is what kind of user interaction do you have in mind. As far as I can see, the Point operator in Xpresso does not allow to delete points.

If a simple script is good enough, the desired effect of deleting points in a given radius is not that complicated. This is the code for a script executed in the Script Manager:

import c4d


def main():
    
    # get null object by name
    nullObj = doc.SearchObject("null")
    # get polygon object by name
    polyObj = doc.SearchObject("polygon")
    
    if nullObj is None:
        return
    if polyObj is None:
        return
    
    # get world space position of null object
    nullObjPos = nullObj.GetMg().off
    
    # get world space matrix and points of the polygon object
    mg = polyObj.GetMg()
    points = polyObj.GetAllPoints()
    
    # prepare the point selection of the polygon object
    selection = polyObj.GetPointS()
    selection.DeselectAll()
    
    # check each point
    for idx, point in enumerate(points):
        
        # get world space position of the point
        pointPos = mg * point
        
        # get the distance from the point to the null object
        diff = pointPos - nullObjPos
        distance = diff.GetLength()
        
        # check distance
        if distance < 100:
            selection.Select(idx)
            
    # delete selected points
    mode = c4d.MODELINGCOMMANDMODE_POINTSELECTION   
    res = c4d.utils.SendModelingCommand(c4d.MCOMMAND_DELETE, list = [polyObj], doc = doc, mode = mode)
    
    c4d.EventAdd()
            
if __name__=='__main__':
    main()

andmotion

@s_bach
Thanks for the quick reply.
That's is simply awesome that you made this code so I can dive in and actually grasp some python basic.

I noticed that also yesterday, Xpresso wont allow me to delete points, I can iterate thru them but I could find the way how to literally delete it.

Will go thru the code and let you know my thoughts, for now THANKS A LOT for help.
Thanks

andmotion

@s_bach

While trying to understand your code some questions raised in my head :

polyObj.GetAllPoints(). Is it not each point vector? If it's I don't
understand the idea of looping thru those vectors to get each pointPos.....
It's hard for me also to pick up the idea of calculation pointPos
inside the for loop. In your code you are multiplying polyObj global Matrix with point.....

At the moment if I have both null and Sphere at 0,0,0 coordinates all points are deleted. if I move sphere a few units in Y axis strangely the middle of the sphere get deleted.

I will spend more time on it to find out the solution. It seems like I will need some kind of channel(slider) while doing if distance < 100 so I could specified the radius by the slider.

I would also need to have this distance updated in real time so when I move null close to the sphere in the viewport the points inside the radius are automatically deleted.

I am really appreciated Sebastian your input here...Thanks

andmotion

Here is the code I am playing with now

import c4d
from c4d import gui
from c4d import utils

#Welcome to the world of Python


def main():
    
    
    nullObj =  doc.SearchObject("Null")
    polyObj = doc.SearchObject("Sphere")
    
    if nullObj:
        print("Null is")
        
    if not nullObj:
        print("no Null")
        
    if polyObj:
        print("Sphere is")
        
    if not polyObj:
        print("no Sphere")
        
    #get nullObj world space position
    nullWSMg = nullObj.GetMg().off
    print nullWSMg
    
    #get matrix and points from polyObj
    polyObjWSMg = polyObj.GetMg().off
    polyObjPointsPos = polyObj.GetAllPoints()
    #print polyObjPointsPos
    print polyObjWSMg
    
    #point selection of the polygon object
    selection = polyObj.GetPointS()
    selection.DeselectAll()
    
    #check each point
    
    for i, point in enumerate(polyObjPointsPos):
        #get WS pos of the points
        pointPos = polyObjWSMg * point
        
        #get the distance from point to the null
        diff = nullWSMg - pointPos
        distance = diff.GetLength()
        
        #check distance
        if distance < 100:
            selection.Select(i)
            
    #delete selected points
    
    mode = c4d.MODELINGCOMMANDMODE_POINTSELECTION
    res = c4d.utils.SendModelingCommand(c4d.MCOMMAND_DELETE, list = [polyObj], doc = doc, mode = mode)
            
    c4d.EventAdd()
    
        
if __name__=='__main__':
    main()

andmotion

Here I uploaded the effect I am after :

I know that using Boole in C4D I can have exactly the same effect BUT my goal is to start from this simple effect as a python journey.
Thanks for any suggestion.
Thanks

ferdinand

Hi,

@andmotion said:

#get matrix and points from polyObj
polyObjWSMg = polyObj.GetMg().off

You did not assign a matrix topolyObjWSMg but the offset vector off the global matrix of polyObj.

@andmotion said:

pointPos = polyObjWSMg * point

Which will make pointPos here not a c4d.Vector but a float - the dot product of two vectors. You also don't have to calculate the global point positions in your loop if you find that distracting, you can just do:

mg = polyObj.GetMg()
global_points = [mg * p for p in polyObj.GetAllPoints()]

distance_squared = 100 ** 2
null_mg = null.GetMg()
for pid, point in enumerate(global_points):
    if (null_mg * point).GetLengthSquared() < distance_squared:
        selection.Select(pid)

And regarding odd behaviour and want you want to do, I would point to my first post. Still sounds to me you actually want to evaluate a gradient.

Cheers
zipit

s_bach

Hello,

PointObject.GetAllPoints() returns a list of vectors; each vector is the object space position of the point of the corresponding index.

To get the world space position, you have to multiply that object space position with the world space matrix.

You find some information on matrix calculations here: Matrix Fundamentals.

If you want to have an interactive slider, you cannot use a script anymore. You have to write a plugin.

As described above, the best way would be to implement the functionality as a ObjectData based generator. This way a procedural workflow could be maintained.

Best wishes,
Sebastian

andmotion

I thing after short research that c4d.plugins.ObjectData could actually be the solution I am after.
I will be posting my progress here.
Once again Thanks Guys for heads up!!!!!
Thanks