Fill Z vertex in Polyline 3d

[AlbertoCañivano2]

My goal is to modify the Z coordinates of a 3d polyline (Camino3d)  from the fields of an attribute table of another feature (Camino).

layer = r'C:\Desmonte_terraplen_vs01.gdb\Camino'
fc_dest = r"C:\Desmonte_terraplen_vs01.gdb\Camino_3D"
with arcpy.da.SearchCursor(layer,["Cota_i","Cota_f"]) as search_cur:
    for search_row in search_cur:
        with arcpy.da.UpdateCursor(fc_dest,["SHAPE@Z"], explode_to_points=True) as upd_cur:
            for upd_row in upd_cur:
                    upd_row[0] = search_row[0]
                    upd_cur.updateRow(upd_row)

Using Explode to point = True I split the polyline into multipoints and I think I can iterate over them.
The problem comes in that I don't know how to iterate inside the Z values of the 3d polyline.
Any suggestions? Thanks a lot!

[JohannesLindner · Accepted solution]

The problem comes in that I don't know how to iterate inside the Z values of the 3d polyline.

A polyline is basically a twodimensional array of vertices:

polyline = [  [point, point, point],  [point, point, point, point, point]  ]

The geometry and its parts are iterable objects, the vertices are arcpy.Point objects.

shape = [r[0] for r in arcpy.da.SearchCursor(layer, ["SHAPE@"])][0]
print("Shape: " + str(shape))
for part in shape:
    print("\tPart: " + str(part))
    for vertex in part:
        print("\t\tVertex: " + str(vertex))
        print("\t\t\tCoordinates: " + str([vertex.X, vertex.Y, vertex.Z, vertex.M]))

You have to construct a new line geometry, updating the vertices as points probably won't get you anywhere.

Assuming that layer and dest_fc are in the same order:

# read the elevation values
endpoint_elevations = [row
                       for row in arcpy.da.SearchCursor(layer, ["Cota_i", "Cota_f"])
                       ]


# start the update cursor for the complete shape token, not just z
with arcpy.da.UpdateCursor(fc_dest, ["SHAPE@"]) as cursor:
    for i, row in enumerate(cursor):
        # get the corresponding elevation values
        start, end = endpoint_elevations[i]
        # interpolate the elevation for each vertex
        # if your fc is m-aware, you can also uncomment the two lines to update the m values
        shape = row[0]
        part = shape[0]
        new_part = []
        slope = (end - start) / shape.length
        m_value = 0
        for v, vertex in enumerate(part):
            if v == 0:
                vertex.Z = start
            else:
                v0 = part[v-1]
                v1 = vertex
                m_value += ((v1.X - v0.X)**2 + (v1.Y - v0.Y)**2)**0.5
                vertex.Z = start + slope * m_value
            #vertex.M = m_value
            new_part.append(vertex)
        # create a new shape and update the feature
        new_shape = arcpy.Polyline(arcpy.Array(new_part),
                                   spatial_reference=shape.spatialReference,
                                   #has_m=True,
                                   has_z=True
                                   )
        cursor.updateRow([new_shape])

[AlbertoCañivano2]

Great response!
I have modified the parameters of the polyline creation tool and it works great.
If I wanted to loop through a feature with more entities to do the same thing, how should I do the loop?

Thanks for your help!

[JohannesLindner]

If the features in Camino and Camino_3D are in the same order, you can just use this script.

If your screenshot was just for testing and you have another structure, you need to explain that structure.

[AlbertoCañivano2]

If you mean geometry type and attribute, Camino and Camino3d are the same structure.
What happens is that for what I am doing, I have defined the axis of the path (Camino3d) and a right and left margin (three 3d polylines inside the same feature with the same Z dimension) inside the EjeCamino feature (sorry for the strange names)