ifcviewer: port unit utilities to C++ in Unit.{h,cpp}

Mirrors selected helpers from ifcopenshell.util.unit: SI prefix multipliers, the conversion-based-unit table (foot/inch/etc -> SI metres), siScaleFromNamedUnit (walks IfcConversionBasedUnit chains down to IfcSIUnit), getUnitAssignment / getProjectUnit / calculateUnitScale, and convert / convertUnit. Lives in src/ifcviewer/ for now alongside Geolocation; will move out when ifcopenshell.util is ported to C++. Needed by upcoming Geolocation fix (e/n/h on IfcMapConversion are in MapUnit, must be converted to metres for the meter-by-default iterator output) and by the federation module (display-unit conversion when the user changes the federation unit). Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-08-20 12:12:15 +00:00 · 2026-05-01 12:12:29 +10:00
parent a2db0a68a4
commit 0d3849737c
2 changed files with 418 additions and 0 deletions
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+/********************************************************************************
+ *                                                                              *
+ * This file is part of IfcOpenShell.                                           *
+ *                                                                              *
+ * IfcOpenShell is free software: you can redistribute it and/or modify         *
+ * it under the terms of the Lesser GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3.0 of the License, or          *
+ * (at your option) any later version.                                          *
+ *                                                                              *
+ * IfcOpenShell is distributed in the hope that it will be useful,              *
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of               *
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                 *
+ * Lesser GNU General Public License for more details.                          *
+ *                                                                              *
+ * You should have received a copy of the Lesser GNU General Public License     *
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.         *
+ *                                                                              *
+ ********************************************************************************/
+
+// Port of selected helpers from
+// src/ifcopenshell-python/ifcopenshell/util/unit.py.  Lives in src/ifcviewer/
+// for now alongside Geolocation; will move out once ifcopenshell.util is
+// ported to C++.
+
+#ifndef UNIT_H
+#define UNIT_H
+
+#include "../ifcparse/express.h"
+
+#include <optional>
+#include <string>
+#include <unordered_map>
+
+namespace ifcopenshell { class file; }
+
+// SI prefix multipliers, e.g. "MILLI" -> 1e-3.  Empty key not present;
+// callers should pass an empty prefix string for "no prefix".
+extern const std::unordered_map<std::string, double> kSiPrefixes;
+
+// SI prefix display symbols, e.g. "MILLI" -> "m".
+extern const std::unordered_map<std::string, std::string> kSiPrefixSymbols;
+
+// Conversion-based unit name (lowercase, IFC convention) -> SI base scale.
+// e.g. "foot" -> 0.3048, "square foot" -> 0.09290304.
+extern const std::unordered_map<std::string, double> kSiConversions;
+
+// Conversion-based unit name -> IFC unit type, e.g. "foot" -> "LENGTHUNIT".
+extern const std::unordered_map<std::string, std::string> kImperialTypes;
+
+// Display symbol per unit name.  Covers IfcSIUnit names ("METRE" -> "m") and
+// IfcConversionBasedUnit names ("foot" -> "ft").
+extern const std::unordered_map<std::string, std::string> kUnitSymbols;
+
+// Returns the multiplier for an SI prefix.  Empty string returns 1.0.
+double getPrefixMultiplier(const std::string& prefix);
+
+// Returns the SI scale for an IfcNamedUnit such that
+//   value_in_unit * scale == value_in_si_base
+// Walks IfcConversionBasedUnit chains down to IfcSIUnit.  Returns nullopt
+// when the chain bottoms out in IfcContextDependentUnit (cannot convert).
+std::optional<double> siScaleFromNamedUnit(express::Base named_unit);
+
+// IfcProject.UnitsInContext (the IfcUnitAssignment).  Returns nullopt if
+// the file has no project or no assignment.
+std::optional<express::Base> getUnitAssignment(ifcopenshell::file* ifc_file);
+
+// First unit in the project's IfcUnitAssignment matching `unit_type`
+// (e.g. "LENGTHUNIT").  Returns nullopt if not found.
+std::optional<express::Base> getProjectUnit(ifcopenshell::file* ifc_file,
+                                            const std::string& unit_type);
+
+// Project unit -> SI base scale (e.g. project in mm => 0.001).  Defaults
+// to 1.0 when no project unit of the requested type is set.
+double calculateUnitScale(ifcopenshell::file* ifc_file,
+                          const std::string& unit_type = "LENGTHUNIT");
+
+// Convert between two units identified by name + optional SI prefix.
+// SQUARE_/CUBIC_ prefixed SI names get the prefix multiplier squared/cubed
+// (matches python ifcopenshell.util.unit.convert).
+double convert(double value,
+               const std::string& from_prefix, const std::string& from_unit,
+               const std::string& to_prefix,   const std::string& to_unit);
+
+// Convert between two IfcNamedUnit entities.  Pulls Name and Prefix off each
+// and delegates to convert().  IfcConversionBasedUnit names that don't appear
+// in kSiConversions return the value unchanged.
+double convertUnit(double value, express::Base from_unit, express::Base to_unit);
+
+#endif // UNIT_H