BUG: Avizo rectilinear export shifts samples by half a voxel

src/Plugins/SimplnxCore/src/SimplnxCore/Filters/Algorithms/WriteAvizoRectilinearCoordinate.cpp から始めてください。ここでは X、Y、Z のサンプル位置が151行目と163行目付近で origin + spacing * index として計算されています。ImageGeom.cpp の331～337行目付近にある半分のspacingによるオフセットと比較してください。提供されたテストケースを src/Plugins/SimplnxCore/test/WriteAvizoRectilinearCoordinateTest.cpp に追加し、[AvizoRectilinearCenters] セレクターを実行してください。ASCII と バイナリの両方のエンコーディングで centers が書き出され（例: X [11,13,15]）、そのテストが通れば完了です。

Problem

WriteAvizoRectilinearCoordinateFilter writes the lower cell corner for each scalar sample instead of its physical center. The ASCII export shifts the measured field by negative half a voxel along each axis. The binary coordinate formula has the same defect, independently of its serialization issue.

Reproduced at fe6c4a15e5a5bffef2523f52cec01be33b1e62a9 using Windows x64, MSVC 19.44, Release, in-memory stores.

Expected coordinate arrays: X [11,13,15], Y [-3.5,-0.5], Z [4]. Actual ASCII arrays: X [10,12,14], Y [-5,-2], Z [2]. The shift is [-1,-1.5,-2].

Steps to Reproduce

1. Create an ImageGeom with dimensions [3,2,1], origin [10,-5,2], and spacing [2,3,4].
2. Attach scalar Int32 cell labels [101,102,103,104,105,106] in X-fastest order, with tuple shape [1,2,3].
3. Preflight and execute the writer with units microns. The test below selects the required encoding(s).
4. Inspect the coordinate metadata/payload against the expectations above. Preflight and execution both succeed.

Cause

src/Plugins/SimplnxCore/src/SimplnxCore/Filters/Algorithms/WriteAvizoRectilinearCoordinate.cpp, lines 151 and 163 uses origin + spacing * index. The ImageGeom center calculation adds half a spacing. The AmiraMesh rectilinear specification, printed page 199 / PDF page 201 stores the X, Y, and Z sample positions in successive arrays, with one coordinate per lattice sample.

Verification Unit Test

Add this case and its local helpers to src/Plugins/SimplnxCore/test/WriteAvizoRectilinearCoordinateTest.cpp. It creates its own input and requires no dataset download. The following complete source was compiled and run in an isolated Catch2 harness linked to the matching Release simplnx and SimplnxCore libraries. No production source was changed.

#include "SimplnxCore/Filters/WriteAvizoRectilinearCoordinateFilter.hpp"
#include "SimplnxCore/Filters/WriteAvizoUniformCoordinateFilter.hpp"
#include "simplnx/Common/Bit.hpp"
#include "simplnx/DataStructure/AttributeMatrix.hpp"
#include "simplnx/DataStructure/DataArray.hpp"
#include "simplnx/DataStructure/Geometry/ImageGeom.hpp"
#include "simplnx/Parameters/FileSystemPathParameter.hpp"
#include "simplnx/UnitTest/UnitTestCommon.hpp"

#include <catch2/catch.hpp>

#include <array>
#include <cstring>
#include <filesystem>
#include <fstream>
#include <iterator>
#include <sstream>

using namespace nx::core;

namespace
{
template <class FilterT>
std::string writeFixture(bool binary, const std::string& name)
{
  UnitTest::LoadPlugins();
  DataStructure dataStructure;
  auto* image = ImageGeom::Create(dataStructure, "Image");
  REQUIRE(image != nullptr);
  image->setDimensions({3, 2, 1});
  image->setOrigin({10.0f, -5.0f, 2.0f});
  image->setSpacing({2.0f, 3.0f, 4.0f});
  auto* cells = AttributeMatrix::Create(dataStructure, "Cells", {1, 2, 3}, image->getId());
  REQUIRE(cells != nullptr);
  image->setCellData(*cells);
  auto* labels = Int32Array::CreateWithStore<Int32DataStore>(dataStructure, "FeatureIds", {1, 2, 3}, {1}, cells->getId());
  REQUIRE(labels != nullptr);
  for(usize index = 0; index < 6; ++index)
  {
    (*labels)[index] = static_cast<int32>(101 + index);
  }
  UnitTest::CheckArraysInheritTupleDims(dataStructure);
  const auto path = std::filesystem::current_path() / name;
  FilterT filter;
  auto args = filter.getDefaultArguments();
  args.insertOrAssign(FilterT::k_OutputFile_Key, std::make_any<FileSystemPathParameter::ValueType>(path));
  args.insertOrAssign(FilterT::k_WriteBinaryFile_Key, std::make_any<bool>(binary));
  args.insertOrAssign(FilterT::k_GeometryPath_Key, std::make_any<DataPath>(DataPath({"Image"})));
  args.insertOrAssign(FilterT::k_FeatureIdsArrayPath_Key, std::make_any<DataPath>(DataPath({"Image", "Cells", "FeatureIds"})));
  args.insertOrAssign(FilterT::k_Units_Key, std::make_any<std::string>("microns"));
  const auto preflight = filter.preflight(dataStructure, args);
  SIMPLNX_RESULT_REQUIRE_VALID(preflight.outputActions);
  const auto execution = filter.execute(dataStructure, args);
  SIMPLNX_RESULT_REQUIRE_VALID(execution.result);
  std::ifstream stream(path, std::ios::binary);
  REQUIRE(stream.is_open());
  return {std::istreambuf_iterator<char>(stream), std::istreambuf_iterator<char>()};
}

usize payloadOffset(const std::string& contents, const std::string& marker)
{
  const auto position = contents.find("\n" + marker);
  REQUIRE(position != std::string::npos);
  const auto newline = contents.find('\n', position + 1);
  REQUIRE(newline != std::string::npos);
  return newline + 1;
}

} // namespace

TEST_CASE("Avizo rectilinear coordinates preserve sample centers", "[AvizoRectilinearCenters]")
{
  const auto contents = writeFixture<WriteAvizoRectilinearCoordinateFilter>(false, "rect_ascii.am");
  const auto offset = payloadOffset(contents, "@2");
  std::istringstream values(contents.substr(offset));
  const std::array<double, 6> expected = {11.0, 13.0, 15.0, -3.5, -0.5, 4.0};
  for(usize component = 0; component < expected.size(); ++component)
  {
    double actual = 0.0;
    REQUIRE(static_cast<bool>(values >> actual));
    CAPTURE(component);
    CHECK(actual == Approx(expected[component]).margin(1.0e-6));
  }
}

The executed harness registered AvizoRectilinearCenters with the Catch2 selector [AvizoRectilinearCenters] and ran:

ctest --test-dir <AvizoContractRepro-build> -C Release -j 1 -R "^AvizoRectilinearCenters$" --output-on-failure

For a standard plugin test build, register the same selector if it is not discovered automatically:

add_test(NAME AvizoRectilinearCenters COMMAND SimplnxCoreUnitTest "[AvizoRectilinearCenters]" --reporter compact)

Observed failure excerpt:

actual == Approx(expected[component]): 10.0 == Approx(11.0)
actual == Approx(expected[component]): -5.0 == Approx(-3.5)
Failed 1 test case, failed 6 assertions.

An independent native control passed for all four writer/encoding combinations: every label, dimension and units string was preserved. Output-overwrite warnings occurred because cases shared their generated filenames; the failures above are numeric assertions, not preflight or file-open failures.

Proposed Fix

In WriteAvizoRectilinearCoordinate::writeData, calculate sample centers as origin + (index + 0.5) * spacing in both encodings. Preserve the current sample counts and X-fastest label ordering. Validate the center coordinates independently of legacy exemplar files; handle binary block serialization in its separate issue.

Notes

Fixes belong on a separate source branch. No fix was applied or tested. Actual Avizo application behavior, other platforms and OOC storage were not tested. This defect blocks a proposed faithful-coordinate export comparison using the existing measured Gille LabDCT ROI.