terra::io::GridLayout2D Struct Reference

Describes the 2D grid layout for a linearized data column. More...

#include <lookup_table_2d_reader.hpp>

Public Attributes
int	nx
	Number of grid points along x.
int	ny
	Number of grid points along y.
double	x_min
	x coordinate of the first (ix=0) grid point
double	y_min
	y coordinate of the first (iy=0) grid point
double	dx
	Grid spacing along x (must be > 0)
double	dy
	Grid spacing along y (must be > 0)
int	stride_x
	Flat-index step when ix increases by 1 (see above)
int	stride_y
	Flat-index step when iy increases by 1 (see above)

Detailed Description

Describes the 2D grid layout for a linearized data column.

A single column in a data file contains nx * ny scalar values (one value per data row), representing a 2D grid where

• the x-axis has nx equally-spaced points: x_min, x_min+dx, ..., x_min+(nx-1)*dx
• the y-axis has ny equally-spaced points: y_min, y_min+dy, ..., y_min+(ny-1)*dy

The flat file index k (0-based, counting only non-comment data rows) maps to the grid index pair (ix, iy) via

k = ix * stride_x + iy * stride_y

Exactly one of stride_x / stride_y must be 1 (the "fast" / innermost dimension); the other equals the size of that fast dimension.

Two common configurations (and their correct stride settings):

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Example A — x varies slowest (C row-major): stride_x = ny, stride_y = 1

Suppose the grid maps pressure (x, 2 points) × temperature (y, 3 points) to density. The data author loops over pressure in the outer loop:

# pressure  temperature  density
#   x=0.0      y=200        row k=0  → (ix=0, iy=0)
  0.0        200          1.10
#   x=0.0      y=300        row k=1  → (ix=0, iy=1)
  0.0        300          1.05
#   x=0.0      y=400        row k=2  → (ix=0, iy=2)
  0.0        400          0.98
#   x=1.0      y=200        row k=3  → (ix=1, iy=0)
  1.0        200          1.08
#   x=1.0      y=300        row k=4  → (ix=1, iy=1)
  1.0        300          1.02
#   x=1.0      y=400        row k=5  → (ix=1, iy=2)
  1.0        400          0.95

For the density column (index 2): nx=2, ny=3. k = ix*3 + iy*1 → stride_x=3 (=ny), stride_y=1

GridLayout2D layout{ .nx=2, .ny=3,
                     .x_min=0.0, .y_min=200.0,
                     .dx=1.0,    .dy=100.0,
                     .stride_x=3,  // ny — one full y-row per x step
                     .stride_y=1 };
auto density = read_lookup_table_2d( "file.dat", 2, layout );
// density( 0.0, 200.0 ) == 1.10   (ix=0, iy=0)
// density( 1.0, 400.0 ) == 0.95   (ix=1, iy=2)

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Example B — y varies slowest (column-major): stride_x = 1, stride_y = nx

Same grid, but the data author loops over temperature in the outer loop:

# pressure  temperature  density
#   x=0.0      y=200        row k=0  → (ix=0, iy=0)
  0.0        200          1.10
#   x=1.0      y=200        row k=1  → (ix=1, iy=0)
  1.0        200          1.08
#   x=0.0      y=300        row k=2  → (ix=0, iy=1)
  0.0        300          1.05
#   x=1.0      y=300        row k=3  → (ix=1, iy=1)
  1.0        300          1.02
#   x=0.0      y=400        row k=4  → (ix=0, iy=2)
  0.0        400          0.98
#   x=1.0      y=400        row k=5  → (ix=1, iy=2)
  1.0        400          0.95

For the density column (index 2): nx=2, ny=3. k = ix*1 + iy*2 → stride_x=1, stride_y=2 (=nx)

GridLayout2D layout{ .nx=2, .ny=3,
                     .x_min=0.0, .y_min=200.0,
                     .dx=1.0,    .dy=100.0,
                     .stride_x=1,  // 1 — consecutive rows differ by one x step
                     .stride_y=2 };// nx — one full x-row per y step
auto density = read_lookup_table_2d( "file.dat", 2, layout );
// density( 0.0, 200.0 ) == 1.10   (ix=0, iy=0)
// density( 1.0, 400.0 ) == 0.95   (ix=1, iy=2)

Both layouts produce the same ScalarLookupTable2D and the same interpolated values — only the file row order differs.

Member Data Documentation

dx

double terra::io::GridLayout2D::dx

Grid spacing along x (must be > 0)

dy

double terra::io::GridLayout2D::dy

Grid spacing along y (must be > 0)

nx

int terra::io::GridLayout2D::nx

Number of grid points along x.

ny

int terra::io::GridLayout2D::ny

Number of grid points along y.

stride_x

int terra::io::GridLayout2D::stride_x

Flat-index step when ix increases by 1 (see above)

stride_y

int terra::io::GridLayout2D::stride_y

Flat-index step when iy increases by 1 (see above)

x_min

double terra::io::GridLayout2D::x_min

x coordinate of the first (ix=0) grid point

y_min

double terra::io::GridLayout2D::y_min

y coordinate of the first (iy=0) grid point

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The documentation for this struct was generated from the following file:

• lookup_table_2d_reader.hpp