[教学]：如何在3D空间根据一组3D点创建一个2D的POLYLINE对象

XDSoft

How to create a new 2D polyline in 3D space?  
ID    17257  
Applies to:    AutoCAD 2000I
AutoCAD 2002
AutoCAD 2000

Date    1/23/2002  

This document is part of    Coordinates and Transformations   Polyline   AcGe (Geometry Library)   ObjectARX     


Question
How do I create a 2d polyline with a set of 3d points that lie in a plane?
Answer
The following code sample does this, please find the whole project attached.

下面的代码,朋友们可以提取几个有用的公共函数,如根据一个点数组中的所有3D点得到他们组成平面的NORMAL向量, 添加对象到块表记录中等等.
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Adesk::Boolean obtainNormal( AcGePoint3dArray &wcsPts, AcGeVector3d &normal )
{
    /* Function endeavors to form 2 non-colinear vectors from points
    in the wcsPts array.
    Once found, the vectors comprise a plane and a normal can be calculated.
    This plane normal must then be perpendicular to vectors formed from
    the remaining points in wcsPts */

    AcGeVector3d xAxis = AcGeVector3d::kIdentity;
    normal = AcGeVector3d::kIdentity;

    int nPts = wcsPts.length();
    for( int i=0; i < nPts ; i++ ) {
        AcGeVector3d vec = wcsPts[(i+1)%nPts] - wcsPts;
        if( vec.isZeroLength() )
            continue;
        else if( !normal.isZeroLength() ) {
            if( vec.isPerpendicularTo( normal ))
                continue;
            else
                return Adesk::kFalse;
        }
            
        else if( xAxis.isZeroLength() )
            xAxis = vec;
        else if( !xAxis.isParallelTo(vec ) ) {
            normal = xAxis.crossProduct( vec ).normal();
        }
    }

    if( normal.isZeroLength() ) {
        if( xAxis.isZeroLength() )
            normal = AcGeVector3d::kZAxis;
        else
            normal = xAxis.perpVector();
    }
    return Adesk::kTrue;
}

Adesk::Boolean
gatherPoints( AcGePoint3dArray &wcsPts, AcGeVector3d &normal )
{
    ads_point prevPt;
    ads_point newPt;
    while( ads_getpoint(wcsPts.length() == 0 ? NULL : prevPt, "\nEnter point
", newPt ) == RTNORM ) {
        acdbUcs2Wcs(newPt, newPt, Adesk::kFalse );

        wcsPts.append( asPnt3d( newPt ) );
        asPnt3d( prevPt ) = asPnt3d( newPt );
        int nPts = wcsPts.length();
        if( nPts >= 2 ) {
            ads_point fromPt, toPt;
            asPnt3d(fromPt) = wcsPts[nPts-2];
            acdbWcs2Ucs(fromPt,fromPt,Adesk::kFalse );
            asPnt3d(toPt) = wcsPts[nPts-1];
            acdbWcs2Ucs(toPt,toPt,Adesk::kFalse );
            ads_grdraw(fromPt, toPt, 1, 0);
        }
    }


    return obtainNormal( wcsPts, normal );
}







void
constructPolyArx( AcGePoint3dArray &wcsPts, AcGeVector3d &normal,
AcDbPolyline*&pPoly)
{
    int nPts = wcsPts.length();
    pPoly = new AcDbPolyline( nPts );
    pPoly->setNormal(normal );

    AcGeMatrix3d mat;
    AcGeVector3d xAxis = normal.perpVector();
    AcGeVector3d yAxis = normal.crossProduct(xAxis);

    // need to transform pts from WCS into UCS of plane:
    // ucsPt = ucsMat.inverse() * wcsPt
    mat.setCoordSystem(
        AcGePoint3d::kOrigin,
        xAxis, yAxis, normal );
    mat = mat.inverse();

    for( int i=0; i < nPts; i++ ) {
        AcGePoint2d pt2d;
        AcGePoint3d pt3d;
        pt3d = mat * wcsPts;
        if( i==0 )
            pPoly->setElevation(pt3d.z);
        pt2d.x = pt3d.x;
        pt2d.y = pt3d.y;


        if( i == nPts-1 && wcsPts == wcsPts[0] )
            pPoly->setClosed(Adesk::kTrue );
        else
            pPoly->addVertexAt(i, pt2d );
    }
    return;
}


Adesk::Boolean
postToMs( AcDbEntity*pEnt)
{
   AcDbBlockTable* pBT;
   if (Acad::eOk != acdbCurDwg()->getBlockTable( pBT, AcDb::kForRead ))
    return Adesk::kFalse;

   AcDbBlockTableRecord* pBTR;
   Acad::ErrorStatus es =
    pBT->getAt( ACDB_MODEL_SPACE, pBTR, AcDb::kForWrite );
   pBT->close();
   if (Acad::eOk != es)
    return Adesk::kFalse;

   es = pBTR->appendAcDbEntity( pEnt );
   pBTR->close();
   return (Acad::eOk == es);
}




void utilsmyarxpoly()
{
// TODO: add your code here

    // function to gather 3d points, and make into a 2d polyline

    AcGePoint3dArray wcsPts;
    AcGeVector3d normal;

    Adesk::Boolean planar = gatherPoints( wcsPts, normal );
    if( !planar || wcsPts.length() < 1 )
        return;

    AcDbPolyline*pPoly;

    constructPolyArx(wcsPts, normal, pPoly );

    postToMs( pPoly );
    pPoly->close();
   

// end of function
}


// TODO: add your other functions here




// END

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wufengl

第一个函数for( int i=0; i= 2 )，还有第二个函数里的for( int i=0; isetElevation(pt3d.z); pt2d和pt3d还没有定义。
这个功能对我很有用，还有生成了这样2D的POLYLINE对象后，如何取得这个对象在WCS下的三维坐标。请晓东帮帮忙

XDSoft

最初由 wufengl 发布
[B]第一个函数for( int i=0; i= 2 )，还有第二个函数里的for( int i=0; isetElevation(pt3d.z); pt2d和pt3d还没有定义。
这个功能对我很有用，还有生成了这样2D的POLYLINE对象后，如何取得这个对象在WCS下的三维坐标。... [/B]

上面的问题是论坛显示的原因，我编辑了帖子，应该都可以显示全了。

2D POLYLINE平面的NORMAL有了，它的对象坐标系也就有了，剩下的就是坐标系变换了，使用AcGeMatrix3d::alignCoordSys ：

1. 
   
2. static AcGeMatrix3d
   
3. 
   
4. alignCoordSys(
   
5. 
   
6. const AcGePoint3d& fromOrigin,
   
7. 
   
8. const AcGeVector3d& fromXAxis,
   
9. 
   
10. const AcGeVector3d& fromYAxis,
    
11. 
    
12. const AcGeVector3d& fromZAxis,
    
13. 
    
14. const AcGePoint3d& toOrigin,
    
15. 
    
16. const AcGeVector3d& toXAxis,
    
17. 
    
18. const AcGeVector3d& toYAxis,
    
19. 
    
20. const AcGeVector3d& toZAxis);
    
21. 
    
22. fromOrigin Input origin point of the from coordinate system
    
23. fromXAxis Input vector defining the x axis of the from coordinate system
    
24. fromYAxis Input vector defining the y axis of the from coordinate system
    
25. fromZAxis Input vector defining the z axis of the from coordinate system
    
26. toOrigin Input origin point of the to coordinate system
    
27. toXAxis Input vector defining the x axis of the to coordinate system
    
28. toYAxis Input vector defining the y axis of the to coordinate system
    
29. toZAxis Input vector defining the z axis of the to coordinate system
    
30. Returns matrix that maps coordinate system with the origin fromOrigin and
    
31. the axes fromXAxis, fromYAxis, and fromZAxis to coordinate system with
    
32. the origin toOrigin and the axes toXAxis, toYAxis, and toZAxis
    
33. 
    
34. 
    

复制代码

可以得到两个坐标系间的转换矩阵，然后用AcGePoint3d::transfromBy 就可以得到另一个坐标系下对应的点的座标了。

2. 
   
3. AcGePoint3d::transformBy Function AcGePoint3d &
   
4. 
   
5. transformBy(
   
6. 
   
7. const AcGeMatrix3d& leftSide);
   
8. 
   
9. leftSide Input transform matrix
   
10. 
    
11. Transform this pre-multiplying it the matrix leftSide.
    
12. 
    
13. Returns the reference to this point.
    
14. 
    
15. Result is the same as setToProduct(leftSide, *this).
    
16. 
    

<br /> AcGePoint3d::transformBy Function AcGePoint3d &<br /> <br /> transformBy(<br /> <br /> const AcGeMatrix3d& leftSide);<br /> <br /> leftSide Input transform matrix <br /> <br /> Transform this pre-multiplying it the matrix leftSide. <br /> <br /> Returns the reference to this point. <br /> <br /> Result is the same as setToProduct(leftSide, *this).<br /> <br />

wufengl

谢谢晓东这么快给了答复