Update sys struct from yaml

CHANGELOG.md

@@ -3,6 +3,18 @@ SPDX-FileCopyrightText: 2025 Uwe Fechner, Bart van de Lint
 SPDX-License-Identifier: MPL-2.0
 -->
 
+# v0.7.1 27-02-2026
+
+## Added
+- `update_sys_struct_from_yaml!()` — update a `SystemStructure` in-place
+  from a modified YAML file (point `pos_cad` and segment `l0`).
+- `segment_cad_length()` and `autocalc_tether_len()` shared helpers,
+  replacing duplicated code in the constructor, `reinit!`, and YAML loader.
+
+## Fixed
+- `SystemStructure` constructor auto-calculates `winch.tether_len` from
+  all connected tethers (was only using the first).
+
 # v0.7.0 DD-02-2026
 
 ## Changed

Project.toml

@@ -1,6 +1,6 @@
 name = "SymbolicAWEModels"
 uuid = "9c9a347c-5289-41db-a9b9-25ccc76c3360"
-version = "0.7.0"
+version = "0.7.1"
 authors = ["Bart van de Lint <bart@vandelint.net> and contributors"]
 
 [deps]

docs/src/exported_functions.md

@@ -34,6 +34,7 @@ simple_linearize!
 
 ```@docs
 load_sys_struct_from_yaml
+update_sys_struct_from_yaml!
 ```
 
 ## System configuration

docs/src/private_functions.md

@@ -127,6 +127,8 @@ SymbolicAWEModels.update_aero_yaml_from_struc_yaml!
 ## SystemStructure internals
 
 ```@docs
+SymbolicAWEModels.segment_cad_length
+SymbolicAWEModels.autocalc_tether_len
 SymbolicAWEModels.assign_indices_and_resolve!
 SymbolicAWEModels.resolve_ref
 SymbolicAWEModels.resolve_ref_spec

src/SymbolicAWEModels.jl

@@ -97,6 +97,7 @@ export update_plot_observables!
 export animate
 export load_sys_struct_from_yaml
 export update_yaml_from_sys_struct!
+export update_sys_struct_from_yaml!
 export update_aero_yaml_from_struc_yaml!
 export replay
 export record

src/system_structure/system_structure_core.jl

@@ -573,7 +573,7 @@ function SystemStructure(name, set;
     end
     for (i, segment) in enumerate(segments)
         @assert segment.idx == i
-        (segment.l0 ≈ 0) && (segment.l0 = norm(points[segment.point_idxs[1]].pos_cad - points[segment.point_idxs[2]].pos_cad))
+        (segment.l0 ≈ 0) && (segment.l0 = segment_cad_length(segment, points))
     end
     for (i, pulley) in enumerate(pulleys)
         @assert pulley.idx == i
@@ -584,9 +584,8 @@ function SystemStructure(name, set;
     for (i, winch) in enumerate(winches)
         @assert winch.idx == i
         if iszero(winch.tether_len)
-            for segment_idx in tethers[winch.tether_idxs[1]].segment_idxs
-                winch.tether_len += segments[segment_idx].l0
-            end
+            winch.tether_len = autocalc_tether_len(
+                winch, tethers, segments)
         end
     end
     # Compute body frame (COM + principal axes) and

src/system_structure/utilities.jl

@@ -13,6 +13,32 @@ This file contains:
 - Segment statistics
 """
 
+# ==================== SHARED HELPERS ==================== #
+
+"""
+    segment_cad_length(segment::Segment, points)
+
+Compute segment length from endpoint `pos_cad` positions.
+"""
+function segment_cad_length(segment::Segment, points)
+    p1 = points[segment.point_idxs[1]]
+    p2 = points[segment.point_idxs[2]]
+    return norm(p1.pos_cad - p2.pos_cad)
+end
+
+"""
+    autocalc_tether_len(winch::Winch, tethers, segments)
+
+Average unstretched tether length across all tethers connected
+to this winch (sum of segment `l0` per tether, then average).
+"""
+function autocalc_tether_len(winch::Winch, tethers, segments)
+    n = length(winch.tether_idxs)
+    return sum(segments[seg_idx].l0
+               for tether_idx in winch.tether_idxs
+               for seg_idx in tethers[tether_idx].segment_idxs) / n
+end
+
 # ==================== TETHER CREATION ==================== #
 
 """
@@ -310,20 +336,17 @@ function reinit!(sys_struct::SystemStructure, set::Settings;
     # Transforms are not updated from Settings - YAML structure geometry has priority
 
     for segment in segments
-        len = norm(points[segment.point_idxs[1]].pos_cad -
-                   points[segment.point_idxs[2]].pos_cad)
+        len = segment_cad_length(segment, points)
         (segment.l0 ≈ 0) && (segment.l0 = len)
         segment.len = len
     end
 
-    # Calculate winch tether_len from settings or sum of segment l0 values
+    # Calculate winch tether_len from settings or segment l0s
     for winch in winches
         l_tether = set.l_tethers[winch.idx]
         if l_tether == 0
-            # Calculate from total segment l0 of all segments in this winch's tethers
-            l_tether = sum(segments[seg_idx].l0
-                           for tether_idx in winch.tether_idxs
-                           for seg_idx in tethers[tether_idx].segment_idxs)
+            l_tether = autocalc_tether_len(
+                winch, tethers, segments)
         end
         winch.tether_len = l_tether
     end

src/yaml_loader.jl

@@ -1012,6 +1012,87 @@ function update_yaml_from_sys_struct!(sys_struct::SystemStructure,
     return nothing
 end
 
+"""
+    update_sys_struct_from_yaml!(sys_struct::SystemStructure,
+                                  struc_yaml::AbstractString)
+
+Update an existing `SystemStructure` in-place from a (possibly modified)
+structural geometry YAML file. Inverse of `update_yaml_from_sys_struct!`.
+
+Updates `pos_cad` for points and `l0` for segments, matched by symbolic
+name. When `l0` is `nothing` in the YAML, it is auto-calculated from the
+endpoint `pos_cad` positions.
+
+Only raw geometry is updated. Call `reinit!(sys_struct, set)` afterward
+to recompute derived quantities (`pos_b`, `pos_w`, wing frames, etc.).
+
+Unmatched names are silently skipped (the YAML may contain a subset of
+components).
+
+# Arguments
+- `sys_struct`: The SystemStructure to update in-place.
+- `struc_yaml`: Path to the structural geometry YAML file.
+
+# Example
+```julia
+sys = load_sys_struct_from_yaml("struc_geometry.yaml"; ...)
+# ... edit YAML externally ...
+update_sys_struct_from_yaml!(sys, "struc_geometry.yaml")
+```
+"""
+function update_sys_struct_from_yaml!(
+        sys_struct::SystemStructure,
+        struc_yaml::AbstractString)
+    yaml_path = isabspath(struc_yaml) ? struc_yaml :
+                joinpath(pwd(), struc_yaml)
+    isfile(yaml_path) ||
+        error("YAML file not found: $yaml_path")
+
+    data = YAML.load_file(yaml_path)
+
+    # --- Update points ---
+    n_points = 0
+    if haskey(data, "points")
+        point_rows = parse_table(data["points"])
+        for row in point_rows
+            haskey(row, :name) || continue
+            name = Symbol(row.name)
+            haskey(sys_struct.points, name) || continue
+
+            point = sys_struct.points[name]
+            point.pos_cad .= KVec3(row.pos_cad...)
+            n_points += 1
+        end
+    end
+
+    # --- Update segment l0 ---
+    n_segments = 0
+    if haskey(data, "segments")
+        segment_rows = parse_table(data["segments"])
+        for row in segment_rows
+            haskey(row, :name) || continue
+            name = Symbol(row.name)
+            haskey(sys_struct.segments, name) || continue
+
+            seg = sys_struct.segments[name]
+
+            # l0: use YAML value, or auto-calc from pos_cad
+            l0_val = haskey(row, :l0) ? row.l0 : nothing
+            if !isnothing(l0_val) && l0_val != "nothing"
+                seg.l0 = Float64(l0_val)
+            else
+                seg.l0 = segment_cad_length(
+                    seg, sys_struct.points)
+            end
+
+            n_segments += 1
+        end
+    end
+
+    @info "update_sys_struct_from_yaml!" n_points n_segments
+    return nothing
+end
+
 """
     update_aero_yaml_from_struc_yaml!(source_struc_yaml, source_aero_yaml,
                                        dest_aero_yaml=source_aero_yaml)

test/test_yaml_update.jl

@@ -0,0 +1,172 @@
+# SPDX-FileCopyrightText: 2025 Bart van de Lint
+# SPDX-License-Identifier: MPL-2.0
+
+# test_yaml_update.jl - Tests for update_sys_struct_from_yaml!
+#
+# Verifies:
+# 1. Unchanged YAML round-trip: pos_cad and l0 unchanged
+# 2. Modified pos_cad: only the changed point is updated
+# 3. Modified segment l0: segment updated correctly
+# 4. l0=nothing in YAML: auto-calc from pos_cad
+
+using Test
+using SymbolicAWEModels
+using SymbolicAWEModels: KVec3
+using LinearAlgebra: norm
+using KiteUtils
+
+const YAML_UPDATE_BASE = """
+points:
+  headers: [name, pos_cad, type, wing_idx, transform_idx,
+            extra_mass, body_frame_damping,
+            world_frame_damping, area, drag_coeff]
+  data:
+    - [pt_a, [1.0, 2.0, 3.0], DYNAMIC, nothing, nothing,
+       1.0, 0.0, 0.0, 0.0, 0.0]
+    - [pt_b, [4.0, 5.0, 6.0], DYNAMIC, nothing, nothing,
+       1.0, 0.0, 0.0, 0.0, 0.0]
+
+segments:
+  headers: [name, point_i, point_j, type, l0,
+            diameter_mm, unit_stiffness, unit_damping,
+            compression_frac]
+  data:
+    - [seg_ab, pt_a, pt_b, POWER_LINE, 10.0,
+       1.0, 5000.0, 10.0, 1.0]
+"""
+
+const SETTINGS_YAML_UPDATE = """
+system:
+    log_file: "data/2plate"
+    g_earth: 9.81
+initial:
+    l_tethers: [0.0]
+    v_reel_outs: [0.0]
+solver:
+    solver: "FBDF"
+    abs_tol: 0.01
+    rel_tol: 0.01
+    relaxation: 0.6
+kite:
+    model: ""
+    foil_file: "ram_air_kite/ram_air_kite_foil.dat"
+    physical_model: "2plate"
+    struc_geometry_path: "struc_geometry.yaml"
+    aero_geometry_path: "aero_geometry.yaml"
+    mass: 0.0
+    quasi_static: false
+tether:
+    cd_tether: 0.958
+    unit_damping: 0.0
+    unit_stiffness: 0.0
+    rho_tether: 724.0
+    e_tether: 5.5e10
+winch:
+    winch_model: "TorqueControlledMachine"
+    drum_radius: 0.110
+    gear_ratio: 1.0
+    inertia_total: 0.024
+    f_coulomb: 122.0
+    c_vf: 30.6
+environment:
+    rho_0: 1.225
+    v_wind: 0.0
+    upwind_dir: -90.0
+    profile_law: 0
+"""
+
+@testset "update_sys_struct_from_yaml!" begin
+    tmpdir = mktempdir()
+    yaml_path = joinpath(tmpdir, "geometry.yaml")
+    write(yaml_path, YAML_UPDATE_BASE)
+
+    settings_path = joinpath(tmpdir, "settings.yaml")
+    write(settings_path, SETTINGS_YAML_UPDATE)
+    system_path = joinpath(tmpdir, "system.yaml")
+    write(system_path, """
+system:
+  sim_settings: settings.yaml
+""")
+
+    set_data_path(tmpdir)
+    set = Settings("system.yaml")
+
+    sys = load_sys_struct_from_yaml(yaml_path;
+        system_name="yaml_update_test", set=set)
+
+    # --------------------------------------------------------
+    # Test 1: Unchanged YAML round-trip
+    # --------------------------------------------------------
+    @testset "Unchanged round-trip" begin
+        orig_a = copy(sys.points[:pt_a].pos_cad)
+        orig_b = copy(sys.points[:pt_b].pos_cad)
+        orig_l0 = sys.segments[:seg_ab].l0
+
+        update_sys_struct_from_yaml!(sys, yaml_path)
+
+        @test sys.points[:pt_a].pos_cad == orig_a
+        @test sys.points[:pt_b].pos_cad == orig_b
+        @test sys.segments[:seg_ab].l0 == orig_l0
+    end
+
+    # --------------------------------------------------------
+    # Test 2: Modified point position
+    # --------------------------------------------------------
+    @testset "Modified point position" begin
+        modified_yaml = replace(
+            YAML_UPDATE_BASE,
+            "[1.0, 2.0, 3.0]" => "[10.0, 20.0, 30.0]")
+        mod_path = joinpath(tmpdir, "modified_pos.yaml")
+        write(mod_path, modified_yaml)
+
+        orig_b = copy(sys.points[:pt_b].pos_cad)
+
+        update_sys_struct_from_yaml!(sys, mod_path)
+
+        @test sys.points[:pt_a].pos_cad ==
+              KVec3(10.0, 20.0, 30.0)
+        # pt_b should be unchanged
+        @test sys.points[:pt_b].pos_cad == orig_b
+    end
+
+    # --------------------------------------------------------
+    # Test 3: Modified segment l0
+    # --------------------------------------------------------
+    @testset "Modified segment l0" begin
+        modified_yaml = replace(
+            YAML_UPDATE_BASE,
+            "10.0,\n       1.0, 5000.0" =>
+            "42.5,\n       1.0, 5000.0")
+        mod_path = joinpath(tmpdir, "modified_l0.yaml")
+        write(mod_path, modified_yaml)
+
+        update_sys_struct_from_yaml!(sys, mod_path)
+
+        @test sys.segments[:seg_ab].l0 == 42.5
+    end
+
+    # --------------------------------------------------------
+    # Test 4: l0=nothing auto-calculates from pos_cad
+    # --------------------------------------------------------
+    @testset "l0=nothing auto-calc from pos_cad" begin
+        # First reset to base YAML so pos_cad is known
+        write(yaml_path, YAML_UPDATE_BASE)
+        update_sys_struct_from_yaml!(sys, yaml_path)
+
+        expected_l0 = norm(
+            KVec3(1.0, 2.0, 3.0) - KVec3(4.0, 5.0, 6.0))
+
+        nothing_yaml = replace(
+            YAML_UPDATE_BASE,
+            "10.0,\n       1.0, 5000.0" =>
+            "nothing,\n       1.0, 5000.0")
+        nothing_path = joinpath(tmpdir, "nothing_l0.yaml")
+        write(nothing_path, nothing_yaml)
+
+        update_sys_struct_from_yaml!(sys, nothing_path)
+
+        @test sys.segments[:seg_ab].l0 ≈ expected_l0
+    end
+
+    rm(tmpdir; recursive=true)
+end