Problems running python script on data tree branches

Replies to This Discussion

Permalink Reply by Marios Tsiliakos on July 29, 2014 at 6:32am

Hello Ben,

Well without the actual script its hard to tell, what goes wrong.

My guess though is that your data managent in the component only works for a provided list of objects, and not a data tree. Getting one branch of the datatree means getting a list.

You have to go through how you interate your first input in your second component.

Best,

M.

Permalink Reply by Ben Minton on July 29, 2014 at 7:13am

Thanks for your fast reply guys,

The python scripts are too long and laborious to post in full, but here's the essence:

I'm basically running through the list of input points as though it were a single list, and generating a list-of-list of the new polygons. I'm then using the nestedListToDataTree function to convert this to a data tree, which I output back into grasshopper.

So my data management is definately only set up to work for a provided list of objects. Should I somehow tell Python to expect an entire data-tree and somehow extract each individual branch from it within the script?

Let me know if you need more info,

Thanks again!

Ben

Permalink Reply by Giulio Piacentino on July 29, 2014 at 8:33am

Hi again Ben

we need more info. Could you please post a simplified version of your script (where maybe the script prints "Hello" for each input that you need?

Thanks

Giulio
--
Giulio Piacentino
for Robert McNeel & Associates
giulio@mcneel.com

Permalink Reply by Ben Minton on July 29, 2014 at 5:24pm

Thanks Giulio,

I've recreated my problem in a very basic script attached here. Each polygon is very simply divided into two, and the points for each half are stored as a list of points within a list of polygons, converted to a data tree.

I think the problem is that each time the Python script runs on a branch it is outputting a list of a list into a data tree format:

[

    [polyA-pt1, polyA-pt2, polyA-pt3] ,

    [polyB-pt1, polyB-pt2, polyB-pt3] ,

]

This means that when the python script is run multiple time on multiple polygons it has to output a list of a list of a list into a data tree:

[

   [

       [polyA-pt1, polyA-pt2, polyA-pt3] ,

       [polyB-pt1, polyB-pt2, polyB-pt3] ,

   ] ,

   [

       [polyD-pt1, polyD-pt2, polyD-pt3] ,

       [polyE-pt1, polyE-pt2, polyE-pt3]

   ]

]

...and this is where the problem seems to be occurring, as in my script the final data tree seems not to have the correct number of levels, and the points are all present but exist on too few branches.

Any help would be much appreciated!

Thanks, Ben

Attachments:

• dataTreeProblem.gh, 13 KB

Permalink Reply by Marios Tsiliakos on July 30, 2014 at 5:03pm

Ben,

I think you should clear out the differences between nested lists and data trees. I know its difficult when you are used to work with arrays but its essential to get the best out of GH. 

Try the following:

import clr
clr.AddReference("Grasshopper")
from Grasshopper.Kernel.Data import GH_Path
from Grasshopper import DataTree

def iterateinput(t):
d1 = DataTree[object]()
for i in range(0,t.BranchCount-1):
polys = t.Branch(i)
poly1 = [polys[0],polys[1],polys[2]]
d1.AddRange(poly1,GH_Path(i,0))
poly1 = [polys[2],polys[3],polys[0]]
d1.AddRange(poly2,GH_Path(i,1))
return d1

outputPolys = iterateinput(inputPoly)

Best,

M.

Attachments:

• dataTreeProblem_rev01.gh, 9 KB

Permalink Reply by Giulio Piacentino on July 31, 2014 at 2:20am

In addition to what Marios wrote:

you should usually not create a DataTree with a List input. The Grasshopper SDK expects either a full tree, or will have to merge those trees in an unpredictable way (which final path is the 'right' path?)

I would really rather ask: what do you want to do in the second script? If you need to handle all inputs together (you need all polygons) there is no way other than setting input as 'Tree Access'.

If handling a list of points (watch out: panels transform anything to text!) is enough, then from a list, set the output to a list, or a single item. There is no other easy way otherwise to predict the right tree indentation (you could, in some scenarios, use ghenv.Component.RunCount but I strongly discourage that).

Please note: your second script is currently running 3 times, in order to account for the 3 lists that you are passing in.

Does it make sense?

Giulio
--
Giulio Piacentino
for Robert McNeel & Associates
giulio@mcneel.com

Permalink Reply by Ben Minton on July 31, 2014 at 5:51am

Hi Guys,

Thanks a lot for your help, I totally get it now. For some reason I was overlooking the fact that the script needs to input and output a data tree. I added a new layer to the logic to iterate through the tree branches, and set up my output to make a data tree from a double nested loop, and now all is good.

Thanks again!

Ben