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Thermal Mapping

Maps the undistorted IR temperature field onto the FEM surface mesh so that measured boundary conditions can be compared to or imposed on the simulation.

Pipeline overview

IR frames (.csv / .irb)
        ↓
  load_irb_txt()
        ↓
  undistort (cv2)          ← K, dist from ir_calib.npz
        ↓
  scale pixels → mm        ← Z / f_x,  Z / f_y
        ↓
  export VTU (meshio)      →  undistorted_thermal.vtu
        ↓
  load FEM mesh (.xdmf)
        ↓
  extract surface nodes (y ≈ 0)
        ↓
  RegularGridInterpolator
        ↓
  export mapped VTU        →  fem_thermal_mapped.vtu

Notebooks

data_io.ipynb

Loads IRB/CSV frames, applies undistortion, and exports the thermal image as a quad VTU mesh in millimetres.

Key cell — VTU export:

calib  = np.load("../data/ir_calib.npz")
K      = calib["K"]
dist   = calib["dist"].flatten()

Z_mm   = 500.0               # camera-to-surface distance
dx_mm  = Z_mm / K[0, 0]     # mm per pixel in x
dy_mm  = Z_mm / K[1, 1]     # mm per pixel in y

Output: results/undistorted_thermal.vtu with point data field temperature (°C).

thermal_mapping.ipynb

Loads the VTU and the FEM mesh, aligns coordinate systems, and resamples.

from scipy.interpolate import RegularGridInterpolator

interp = RegularGridInterpolator((ty, tx), T_img, method="linear",
                                  bounds_error=False, fill_value=np.nan)
T_surface = interp(np.column_stack([y_q, x_q]))

Transform parameters — adjust to your setup:

Variable Meaning
FACE_Y y-coordinate of the FEM face visible to the camera
scale_x, scale_y Ratio of thermal extent to FEM extent
offset_x, offset_y Manual shift to align image to mesh (mm)

Output: results/fem_thermal_mapped.vtu with point field temperature_ir (NaN on interior nodes).

Viewing in ParaView

  1. Open fem_thermal_mapped.vtu
  2. Color by temperature_ir
  3. Apply Threshold filter to hide NaN interior nodes if needed

To overlay simulation and measurement:

  1. Open both temperature.xdmf (FEM result) and fem_thermal_mapped.vtu
  2. Add Calculator filter: temperature_sim - temperature_ir → residual field