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ACIS SAT 文件格式详解及其解析

news 2026/5/12 13:51:06

SAT 文件格式概述

什么是 SAT 文件？

ACIS SAT（Standard ACIS Text）文件是由 Spatial 公司开发的 ACIS 几何建模内核使用的标准文件格式。它是一种文本格式，用于存储三维几何模型的边界表示（B-Rep）数据，包括：

几何信息：点、线、面、体等几何实体的数学定义
拓扑信息：顶点、边、环、面、壳等拓扑实体及其连接关系
属性信息：颜色、名称、图层等附加属性
NURBS 支持：完整的 NURBS（非均匀有理 B 样条）曲线和曲面表示

SAT 文件的特点

文本格式：人可读，便于调试和分析
版本号标识：文件开头明确标注 ACIS 版本
实体编号系统：每个实体有唯一的 ID 和引用计数
前向引用：支持实体间的相互引用
灵活的扩展性：支持自定义属性和扩展字段

文件结构与版本

文件头格式

ACIS 100 ACIS Verifier status: 0

ACIS：固定标识符
100：主版本号（如 700 表示 v7.0，3300 表示 v33.0）
ACIS Verifier status: 0：验证状态

实体记录格式

每个实体记录遵循以下格式：

<count> <entity-type> <ref1> <ref2> ... <data-fields> { <nested-data> }

示例：

-40 intcurve-curve $-1 -1 -1 $-1 forward { exactcur 6 full nurbs 3 open 2 ... }

字段说明：

-40：实体编号（负数表示引用计数）
intcurve-curve：实体类型（相交曲线）
$-1 -1 -1 $-1：前置引用（$ 表示向前引用）
forward：方向标志
{ ... }：嵌套数据块

主要实体类型

几何实体

point - 点
straight-curve - 直线
circle-curve - 圆
ellipse-curve - 椭圆
intcurve-curve - 参数曲线（含 NURBS）
plane-surface - 平面
cylinder-surface - 圆柱面
cone-surface - 圆锥面
exactsur - 精确曲面（含 NURBS）

拓扑实体

vertex - 顶点
edge - 边
coedge - 协同边（有向边）
loop - 环
face - 面
shell - 壳
lump - 体块
body - 实体

核心解析类设计

类图概览

classDiagram%% 核心流类class SATInputStream {+std::istream& stream+size_t lineNumber+peekToken() String+nextToken() String+readInt() int+readDouble() double+readString() String+readEntityRef() int+readFlagsUntilNumber() List~String~+static IsNumber(token) bool+static hasFlag(flags, flag) bool}%% 基础实体类class SATEntity {#int m_satId#int m_refCount#SATEntityType m_type+getSatId() int+getRefCount() int+getType() SATEntityType+virtual Import(stm) void+virtual ResolvePointers() void}class SATFactory {+static createEntity(type, id) SATEntity*+static registerType(type, factory) void}%% 几何实体层次class SATGeometry {+virtual GetCurve() Geom_Curve+virtual GetSurface() Geom_Surface}class SATPoint {-double m_x, m_y, m_z+Import(stm) void+GetPoint() gp_Pnt}class SATCurve {#Handle(Geom_Curve) m_curve+GetCurve() Geom_Curve}class SATIntersectionCurve {-int m_degree-bool m_isRational-List~double~ m_knots-List~int~ m_multiplicities-List~gp_Pnt~ m_controlPoints-List~double~ m_weights+Import(stm) void+buildBSplineCurve() void}class SATSurface {#Handle(Geom_Surface) m_surface+GetSurface() Geom_Surface}class SATExactSurface {-int m_uDegree, m_vDegree-bool m_isRational-List~List~gp_Pnt~ m_controlPoints-List~List~double~ m_weights+Import(stm) void+buildBSplineSurface() void}%% 拓扑实体层次class SATTopology {+TopoDS_Shape GetShape()}class SATVertex {-SATPoint* m_point+ResolvePointers() void+GetShape() TopoDS_Vertex}class SATEdge {-SATCurve* m_curve-SATVertex* m_start, *m_end+ResolvePointers() void+GetShape() TopoDS_Edge}class SATFace {-SATSurface* m_surface-List~SATLoop~ m_loops+ResolvePointers() void+GetShape() TopoDS_Face}%% 文件解析器class SATFile {-String filename-Map~int, SATEntity~ entities-Load() bool-BuildTopology() TopoDS_Shape-ExportBREP(shape, file) bool}%% 关系定义SATInputStream --> SATEntity : 读取数据SATFactory --> SATEntity : 创建实例SATEntity <|-- SATGeometrySATEntity <|-- SATTopologySATCurve <|-- SATIntersectionCurveSATSurface <|-- SATExactSurfaceSATFile --> SATEntity : 管理所有实体SATFile --> SATInputStream : 使用流解析

核心类详解

1. SATInputStream - 流式解析器

职责：提供 token 级别的流式读取功能

关键方法：

class SATInputStream {
public:std::string peekToken();      // 预读下一个 token，不消耗std::string nextToken();      // 读取并消耗下一个 tokenint readInt();                // 读取整数double readDouble();          // 读取浮点数std::string readString();     // 读取字符串int readEntityRef();          // 读取实体引用（跳过 $ 标记）std::vector<std::string> readFlagsUntilNumber(); // 读取标志直到数字static bool IsNumber(const std::string& token);static bool hasFlag(const std::vector<std::string>& flags, const std::string& flag);
};

设计亮点：

Token 预读机制，支持前瞻解析
自动跳过空白字符和注释
行号跟踪，便于错误定位
静态辅助函数，支持类型检测和标志判断

2. SATEntity - 实体基类

职责：所有 SAT 实体的抽象基类

关键特性：

enum class SATEntityType {POINT, CURVE, SURFACE,   // 几何实体VERTEX, EDGE, FACE,      // 拓扑实体LOOP, COEDGE, SHELL,     // 拓扑实体LUMP, BODY, ATTRIBUTE    // 其他实体
};class SATEntity {
protected:int m_satId;              // SAT 文件中的实体 IDint m_refCount;           // 引用计数SATEntityType m_type;     // 实体类型public:virtual void Import(SATInputStream& stm) = 0;  // 从流导入数据virtual void ResolvePointers();                // 解析引用（第二阶段）int GetSatId() const { return m_satId; }SATEntityType GetType() const { return m_type; }
};

两阶段解析模式：

Import 阶段：读取自身数据，保存引用 ID
ResolvePointers 阶段：根据引用 ID 查找并建立指针链接

3. SATFactory - 工厂类

职责：根据实体类型动态创建对应的解析器实例

实现原理：

class SATFactory {
private:static std::map<std::string, EntityCreator> creators;public:static SATEntity* createEntity(const std::string& type, int id) {if (creators.find(type) == creators.end()) {std::cerr << "WARNING: No factory for '" << type << "'" << std::endl;return nullptr;}return creators[type](id);}static void registerType(const std::string& type, EntityCreator creator) {creators[type] = creator;}
};

注册示例：

// 在初始化时注册所有实体类型
SATFactory::registerType("point", [](int id) { return new SATPoint(id); });
SATFactory::registerType("intcurve-curve", [](int id) { return new SATIntersectionCurve(id); });
SATFactory::registerType("exactsur", [](int id) { return new SATExactSurface(id); });

几何实体解析

点（SATPoint）

最简单的几何实体：

void SATPoint::Import(SATInputStream& stm) {auto header = stm.readEntityHeader();// 读取三个坐标值m_x = stm.readDouble();m_y = stm.readDouble();m_z = stm.readDouble();
}gp_Pnt SATPoint::GetPoint() const {return gp_Pnt(m_x, m_y, m_z);
}

参数曲线（SATIntersectionCurve）

最复杂的曲线类型，支持 NURBS：

void SATIntersectionCurve::Import(SATInputStream& stm) {// 1. 读取实体头auto header = stm.readEntityHeader();// 2. 跳过前置标记直到 "{"skipPrecedingTokens(stm);// 3. 读取曲线类型及基础信息std::string curveType = stm.readString();  // "exactcur"int version = stm.readInt();               // 版本号std::string flags = stm.readString();      // "full"std::string curveKind = stm.readString();  // "nurbs" 或 "nubs"// 根据标志设置理性标志m_isRational = (curveKind == "nurbs");int dimension = stm.readInt();             // 维度（通常是 3）std::string knotType = stm.readString();   // open/closed/periodicm_degree = stm.readInt();                  // 阶数// 节点对数量 - 版本 6+ 才有此字段int knotPairs = 0;if (version >= 6) {knotPairs = stm.readInt();}// 4. 读取节点向量for (int i = 0; i < knotPairs; ++i) {double knot = stm.readDouble();int mult = stm.readInt();// 端点重复度修正if ((i == 0 || i == knotPairs - 1) && mult == m_degree) {mult = m_degree + 1;}m_knots.push_back(knot);m_multiplicities.push_back(mult);}// 5. 读取控制点（根据是否有理决定是否读取权重）while (true) {std::string token = stm.peekToken();if (!SATInputStream::IsNumber(token) || token == "}") break;double x = stm.readDouble();double y = stm.readDouble();double z = stm.readDouble();double w = 1.0;if (m_isRational) {// 有理曲线：必须有权重if (SATInputStream::IsNumber(stm.peekToken())) {w = stm.readDouble();}}m_controlPoints.push_back(gp_Pnt(x, y, z));m_weights.push_back(w);m_controlPointCount++;}// 6. 跳过尾部固定字段skipTrailingFields(stm);// 7. 构建 OCCT B-Spline 曲线buildBSplineCurve();
}

关键设计决策：

nurbs vs nubs：
- nurbs（Non-Uniform Rational B-Spline）：有理 B 样条，需要读取权重
- nubs（Non-Uniform B-Spline）：非有理 B 样条，不需要权重

节点向量展开：

// 压缩格式：knot=0, mult=3; knot=1, mult=3
// 展开后：[0, 0, 0, 1, 1, 1]
TColStd_Array1OfReal knots(1, expandedSize);
int idx = 1;
for (size_t i = 0; i < m_knots.size(); ++i) {for (int j = 0; j < m_multiplicities[i]; ++j) {knots(idx++) = m_knots[i];}
}

有理曲线构造：

if (m_isRational) {m_curve = new Geom_BSplineCurve(poles, weights, knots, mults, degree, false);
} else {m_curve = new Geom_BSplineCurve(poles, knots, mults, degree, false);
}

NURBS 曲面解析（SATExactSurface）

数据格式

exactsur version rational_flag u_degree v_degree u_knot_pairs v_knot_pairsu_knots... v_knots...control_points_with_weights...

解析流程

void SATExactSurface::Import(SATInputStream& stm) {// 1. 读取基本信息auto header = stm.readEntityHeader();skipPrecedingTokens(stm);std::string type = stm.readString();  // "exactsur"int version = stm.readInt();int rationalFlag = stm.readInt();     // 3=nubs, other=nurbsm_isRational = (rationalFlag != 3);// 2. 读取次数m_uDegree = stm.readInt();m_vDegree = stm.readInt();// 3. 读取节点对数量int uKnotPairs = stm.readInt();int vKnotPairs = stm.readInt();// 4. 读取 U 方向节点向量for (int i = 0; i < uKnotPairs; ++i) {double knot = stm.readDouble();int mult = stm.readInt();m_uKnots.push_back(knot);m_uMultiplicities.push_back(mult);}// 5. 读取 V 方向节点向量for (int i = 0; i < vKnotPairs; ++i) {double knot = stm.readDouble();int mult = stm.readInt();m_vKnots.push_back(knot);m_vMultiplicities.push_back(mult);}// 6. 读取控制点网格（带权重）readControlPointGrid(stm);// 7. 跳过尾部字段skipTrailingFields(stm);// 8. 构建 OCCT NURBS 曲面buildBSplineSurface();
}

控制点网格读取

void SATExactSurface::readControlPointGrid(SATInputStream& stm) {m_controlPoints.clear();m_weights.clear();std::vector<double> currentRow;std::vector<double> weightRow;while (!stm.eof() && !stm.isToken("#")) {std::string token = stm.peekToken();// 检查是否遇到结束标记if (token == "}" || token == "#") break;// 尝试读取 4 个值（x, y, z, weight）if (SATInputStream::IsNumber(token)) {double x = stm.readDouble();double y = stm.readDouble();double z = stm.readDouble();// 有理曲面必须读取权重double w = 1.0;if (m_isRational && SATInputStream::IsNumber(stm.peekToken())) {w = stm.readDouble();}currentRow.push_back(x);currentRow.push_back(y);currentRow.push_back(z);weightRow.push_back(w);// 每 3 个值（xyz）完成一个控制点if (currentRow.size() % 3 == 0) {// 检查是否需要开始新行（通过检测下一行的第一个值）if (shouldStartNewRow(stm)) {addControlPointRow(currentRow, weightRow);currentRow.clear();weightRow.clear();}}} else {break;}}// 添加最后一行if (!currentRow.empty()) {addControlPointRow(currentRow, weightRow);}
}

NURBS 曲面构建

void SATExactSurface::buildBSplineSurface() {try {// 1. 展开节点向量auto [uKnots, uMults] = expandKnotVector(m_uKnots, m_uMultiplicities);auto [vKnots, vMults] = expandKnotVector(m_vKnots, m_vMultiplicities);// 2. 构建控制点数组int uSize = getUControlPointSize();int vSize = getVControlPointSize();TColgp_Array2OfPnt poles(1, uSize, 1, vSize);TColStd_Array2OfReal weights(1, uSize, 1, vSize);for (int i = 0; i < uSize; ++i) {for (int j = 0; j < vSize; ++j) {poles(i+1, j+1) = m_controlPoints[i][j];weights(i+1, j+1) = m_weights[i][j];}}// 3. 创建 OCCT NURBS 曲面if (m_isRational) {m_surface = new Geom_BSplineSurface(poles, weights,uKnots, vKnots,uMults, vMults,m_uDegree, m_vDegree,false, false  // not periodic);} else {m_surface = new Geom_BSplineSurface(poles,uKnots, vKnots,uMults, vMults,m_uDegree, m_vDegree,false, false);}} catch (const Standard_ConstructionError& e) {std::cerr << "ERROR: Failed to build NURBS surface: " << e.GetMessageString() << std::endl;fallbackToPlane();}
}

拓扑实体解析

边（SATEdge）

void SATEdge::Import(SATInputStream& stm) {auto header = stm.readEntityHeader();// 读取曲线引用m_curveId = stm.readEntityRef();// 读取参数范围m_firstParameter = stm.readOptionalDouble();m_lastParameter = stm.readOptionalDouble();// 读取 PCurves（可选）readPCurves(stm);// 读取同侧标记m_sameSense = stm.readBoolean();
}void SATEdge::ResolvePointers() {// 查找引用的曲线SATCurve* curve = getFile()->getCurveById(m_curveId);// 创建 OCCT 边TopoDS_Edge edge = BRepBuilderAPI_MakeEdge(curve->GetCurve(), m_firstParameter, m_lastParameter);m_shape = edge;
}

面（SATFace）

void SATFace::Import(SATInputStream& stm) {auto header = stm.readEntityHeader();// 读取曲面引用m_surfaceId = stm.readEntityRef();// 读取边界环while (!stm.isToken("#")) {int loopId = stm.readEntityRef();m_loopIds.push_back(loopId);}// 读取 2D 参数（可选）read2DParameters(stm);
}void SATFace::ResolvePointers() {// 获取曲面SATSurface* surface = getFile()->getSurfaceById(m_surfaceId);// 创建面TopoDS_Face face = BRepBuilderAPI_MakeFace(surface->GetSurface(), Precision::Confusion());// 添加边界环for (int loopId : m_loopIds) {SATLoop* loop = getFile()->getLoopById(loopId);TopoDS_Wire wire = loop->GetWire();if (loop.isOuter()) {face.Add(wire);  // 外环} else {face.Add(wire);  // 内环（孔）}}m_shape = face;
}

错误处理与容错机制

1. 版本兼容性处理

int SATIntersectionCurve::readVersionAware(SATInputStream& stm) {int version = stm.readInt();// 不同版本有不同的字段顺序if (version < 6) {// Version 4: 没有 knotPairs 字段，需要动态检测return readLegacyFormat(stm);} else {// Version 6+: 标准格式return readStandardFormat(stm);}
}

2. 回退策略（Fallback）

Handle(Geom_Surface) SATExactSurface::GetSurface() {if (!m_surface.IsNull()) {return m_surface;}try {buildBSplineSurface();} catch (const Standard_ConstructionError& e) {std::cerr << "ERROR: NURBS surface construction failed, falling back to plane" << std::endl;// 回退到平面fallbackToPlane();}return m_surface;
}void SATExactSurface::fallbackToPlane() {// 尝试用前三个控制点构造平面if (m_controlPoints.size() >= 3) {gp_Pnt p1 = m_controlPoints[0][0];gp_Pnt p2 = m_controlPoints[0][1];gp_Pnt p3 = m_controlPoints[1][0];gp_Vec v1(p1, p2);gp_Vec v2(p1, p3);gp_Dir normal = v1.Crossed(v2);m_surface = new Geom_Plane(p1, normal);} else {// 默认 XY 平面m_surface = new Geom_Plane(gp::XOY());}
}

3. 形状修复协议

TopoDS_Shape SATFile::BuildTopology() {TopoDS_Compound compound;BRep_Builder builder;builder.MakeCompound(compound);// 1. 构建所有拓扑实体for (auto& entity : entities) {if (entity->isBody()) {TopoDS_Shape shape = entity->GetShape();if (!shape.IsNull()) {builder.Add(compound, shape);}}}// 2. 应用 ShapeFix 修复ShapeFix_Shape fix(compound);fix.SetPrecision(Precision::Confusion());fix.SetMaxTolerance(1e-3);fix.Perform();return fix.Shape();
}