Nodes

Adding nodes

Nodes can be added manually at prescribed spatial co-ordinates with the .add_node() and .add_nodes() methods, where xyz is given as a list of co-ordinates for a single node with .add_node(), and for nodes as a list of lists for multiple node co-ordinates when using .add_nodes(). If integer values for co-ordinates are given, they are converted to floats before adding to the Structure object. A mass can be added also, which is needed for some specific compas_fea functionality.

mdl.add_node(xyz=[-5, -5, 0])  # add a single node at x=-5, y=-5, z=0

mdl.add_nodes(nodes=[[5, -5, 0], [5, 5, 0], [-5, 5, 0], [0, 0, 5]])  # add four nodes at one time

Viewing nodes

The nodes data are Node objects stored in the .nodes dictionary, and are added with integer keys numbered sequentially starting from 0 (Python based). The data summary for each node can be viewed by printing the Node to the terminal.

>>> print(mdl.nodes[3])  # print a summary of node number 3

compas_fea Node object
----------------------
key   : 3
x     : -5.0
y     : 5.0
z     : 0.0
ex    : [1, 0, 0]
ey    : [0, 1, 0]
ez    : [0, 0, 1]
mass  : 0

Individually, all of the Node attributes are accessible for inspection.

>>> mdl.nodes[3]  # node number 3
Node(3)

>>> mdl.nodes[3].key  # the key of node number 3
3

>>> mdl.nodes[3].x  # the x coordinate of node number 3
-5.0

>>> mdl.nodes[3].ex  # the local axis of node number 3
[1, 0, 0]

Editing nodes

To edit the data of a node use the .edit_node() method, which will change both the data of the Node and update the .node_index dictionary (explained later) if the co-ordinates were changed during editing.

>>> print(mdl.nodes[3].x, mdl.nodes[3].z)  # print the x and z coordinates of node number 3
-5.0 0.0

>>> mdl.edit_node(key=3, attr_dict={'x': 0.0, 'z': 4.0})  # update x and z values

>>> print(mdl.nodes[3].x, mdl.nodes[3].z)  # print the new x and z coordinates
0.0 4.0

Methods

The co-ordinates of a given node or many nodes, and the total number of nodes in the Structure, may be evaluated with the .node_xyz(), .nodes_xyz() and .node_count() methods:

>>> mdl.node_xyz(node=3)  # fetch the coordinates of node number 3
[-5.0, 5.0, 0.0]

>>> mdl.nodes_xyz(nodes=[3, 4])  # fetch the coordinates of nodes 3 and 4
[[-5.0, 5.0, 0.0], [5.0, 0.0, 2.0]]

If nodes is not given for .nodes_xyz(), then all of the node coordinates will be returned.

>>> mdl.node_count()  # get the count of nodes in the structure
5

The simple bounding box made by the Structure can be found by calling the .node_bounds() method. This will return three lists, containing the minimum and maximum x, y and z co-ordinates of the node coordinates in .nodes.

>>> mdl.node_bounds()  # return [xmin, xmax], [ymin, ymax], [zmin, zmax]
([-5.0, 5.0], [-5.0, 5.0], [0.0, 5.0])

It can be checked if a node is already present in the Structure object by a query with the method .check_node_exists() and with a list of test node co-ordinates. If a node exists at those coordinates, then the method will return the integer key, if not, None will be returned. Integer values that are given for co-ordinates will be converted to floats during this check.

>>> mdl.check_node_exists(xyz=[5, 5, 0])  # does a node exist at x=5, y=5, z=0
2

>>> mdl.check_node_exists(xyz=[5, 5, -1])  # does a node exist at x=5, y=5, z=-1
None

Note: no more than one node can exist for the same co-ordinates, i.e. no overlapping nodes are allowed, this ensures a unique entry in the node index dictionary (see below) and is currently important for many operations in compas_fea.

Node index

The Structure object’s node index is a geometric key to integer key dictionary accessed through .node_index. The geometric key is the string representation of the node’s co-ordinates to a prescribed (default 3) float precision, while the value that is returned for this geometric key is the node’s number. The node index can be used to quickly see what node number corresponds to a nodal spatial location. Note: the .node_index should never be edited manually.

>>> mdl.node_index  # show the current node index dictionary
{'-5.000,-5.000,0.000': 0, '5.000,-5.000,0.000': 1, '5.000,5.000,0.000': 2, '-5.000,5.000,0.000': 3}