OpenCASCADE BRep Projection
一网友发邮件问我下图所示的效果如何在OpenCASCADE中实现，我的想法是先构造出螺旋线，再将螺旋线投影到面上。
为了验证我的想法，结合原来螺旋线的造型算法，来测试下这种效果的实现。依然采用Tcl脚本在Draw Test Harness中试验。个人觉得高效使用OpenCASCADE的方法应该也是先用Tcl脚本来验证一些想法后，再根据使用到的命令找到OpenCASCADE中DRAW的命令实现，最后再可以根据DRAW中的实现，翻译成C++代码了。
使用下列Tcl脚本生成效果和上图就很类似了，Tcl脚本代码如下所示：
#
# wrap a curve to a surface.
# Shing Liu(eryar@163.com)
# 2016-08-16 22:50
#
pload ALL
cone aCone 18*pi 2
trim aCone aCone 0 2*pi 0 2*pi
line aLine2d 0 0 2 1
trim aSegment aLine2d 0 2*pi
mkedge aHelixEdge aSegment aCone 0 6*pi
# there is no curve 3d in the pcurve edge.
mkedgecurve aHelixEdge 0.001
ttranslate aHelixEdge 10 20 10
bsplinesurf aSurface \
5 5 0 6 1 1 4 1 5 1 8 6 \
5 5 0 6 2 1 3 1 6 1 7 6 \
0 0 0 1 2 0 0 1 5 0 - 1 1 10 0 5 1 12 0 1 1 15 0 - 3 1 16 0 - 3 1 19 0 - 4 1 24 0 0 1 \
0 10 2 1 3 10 0 1 8 10 5 1 10 10 3 1 12 10 2 1 15 10 0 1 20 10 5 1 21 10 3 1 24 10 0 1 \
0 20 10 1 4 20 4 1 7 20 4 1 10 20 20 1 12 20 10 1 16 20 4 1 19 20 4 1 20 20 10 1 24 20 0 1 \
0 30 0 1 2 30 0 1 8 30 0 1 10 30 0 1 12 30 0 1 14 30 0 1 20 30 0 1 22 30 0 1 24 30 0 1 \
0 40 - 1 1 4 40 5 1 9 40 1 1 10 40 5 1 12 40 - 1 1 16 40 5 1 21 40 1 1 22 40 5 1 24 40 0 1 \
0 50 5 1 4 50 10 1 6 50 10 1 10 50 5 1 12 50 5 1 16 50 10 1 18 50 10 1 20 50 5 1 24 50 0 1 \
0 60 4 1 3 60 - 3 1 7 60 - 4 1 10 60 4 1 12 60 4 1 15 60 - 3 1 19 60 - 4 1 20 60 4 1 24 60 0 1 \
0 70 - 5 1 3 70 0 1 5 70 0 1 10 70 - 3 1 12 70 - 5 1 15 70 0 1 17 70 0 1 20 70 - 3 1 24 70 0 1 \
0 80 7 1 3 80 1 1 7 80 3 1 10 80 0 1 12 80 7 1 15 80 1 1 19 80 3 1 21 80 0 1 24 80 0 1
mkface aFace aSurface
# use BRepProj_Projection
prj aResult aHelixEdge aFace 0 0 1
vdisplay aHelixEdge aFace aResult_1
# wrap a curve to a surface.
# Shing Liu(eryar@163.com)
# 2016-08-16 22:50
#
pload ALL
cone aCone 18*pi 2
trim aCone aCone 0 2*pi 0 2*pi
line aLine2d 0 0 2 1
trim aSegment aLine2d 0 2*pi
mkedge aHelixEdge aSegment aCone 0 6*pi
# there is no curve 3d in the pcurve edge.
mkedgecurve aHelixEdge 0.001
ttranslate aHelixEdge 10 20 10
bsplinesurf aSurface \
5 5 0 6 1 1 4 1 5 1 8 6 \
5 5 0 6 2 1 3 1 6 1 7 6 \
0 0 0 1 2 0 0 1 5 0 - 1 1 10 0 5 1 12 0 1 1 15 0 - 3 1 16 0 - 3 1 19 0 - 4 1 24 0 0 1 \
0 10 2 1 3 10 0 1 8 10 5 1 10 10 3 1 12 10 2 1 15 10 0 1 20 10 5 1 21 10 3 1 24 10 0 1 \
0 20 10 1 4 20 4 1 7 20 4 1 10 20 20 1 12 20 10 1 16 20 4 1 19 20 4 1 20 20 10 1 24 20 0 1 \
0 30 0 1 2 30 0 1 8 30 0 1 10 30 0 1 12 30 0 1 14 30 0 1 20 30 0 1 22 30 0 1 24 30 0 1 \
0 40 - 1 1 4 40 5 1 9 40 1 1 10 40 5 1 12 40 - 1 1 16 40 5 1 21 40 1 1 22 40 5 1 24 40 0 1 \
0 50 5 1 4 50 10 1 6 50 10 1 10 50 5 1 12 50 5 1 16 50 10 1 18 50 10 1 20 50 5 1 24 50 0 1 \
0 60 4 1 3 60 - 3 1 7 60 - 4 1 10 60 4 1 12 60 4 1 15 60 - 3 1 19 60 - 4 1 20 60 4 1 24 60 0 1 \
0 70 - 5 1 3 70 0 1 5 70 0 1 10 70 - 3 1 12 70 - 5 1 15 70 0 1 17 70 0 1 20 70 - 3 1 24 70 0 1 \
0 80 7 1 3 80 1 1 7 80 3 1 10 80 0 1 12 80 7 1 15 80 1 1 19 80 3 1 21 80 0 1 24 80 0 1
mkface aFace aSurface
# use BRepProj_Projection
prj aResult aHelixEdge aFace 0 0 1
vdisplay aHelixEdge aFace aResult_1
上述代码主要使用了Draw 命令prj，找到prj的实现代码如下所示：
static Standard_Integer prj(Draw_Interpretor& di, Standard_Integer n,
const
char** a)
{
char newname[255];
if (n < 7) return 1;
TopoDS_Shape InpLine = DBRep::Get(a[2]);
TopoDS_Shape InpShape = DBRep::Get(a[3]);
Standard_Real DX=Draw::Atof(a[4]),DY=Draw::Atof(a[5]),DZ=Draw::Atof(a[6]);
gp_Dir TD(DX,DY,DZ);
BRepProj_Projection Prj(InpLine,InpShape,TD);
Standard_Integer i = 1;
char* temp = newname;
if (Prj.IsDone()) {
while (Prj.More()) {
Sprintf(newname,"%s_%d",a[1],i);
DBRep::Set(temp,Prj.Current());
// cout<<newname<<" ";
di<<newname<<" ";
i++;
Prj.Next();
}
}
// cout<<endl;
di<<"\n";
return 0;
}
{
char newname[255];
if (n < 7) return 1;
TopoDS_Shape InpLine = DBRep::Get(a[2]);
TopoDS_Shape InpShape = DBRep::Get(a[3]);
Standard_Real DX=Draw::Atof(a[4]),DY=Draw::Atof(a[5]),DZ=Draw::Atof(a[6]);
gp_Dir TD(DX,DY,DZ);
BRepProj_Projection Prj(InpLine,InpShape,TD);
Standard_Integer i = 1;
char* temp = newname;
if (Prj.IsDone()) {
while (Prj.More()) {
Sprintf(newname,"%s_%d",a[1],i);
DBRep::Set(temp,Prj.Current());
// cout<<newname<<" ";
di<<newname<<" ";
i++;
Prj.Next();
}
}
// cout<<endl;
di<<"\n";
return 0;
}
如上述代码所示，主要使用了类BRepProj_Projection，此类的主要功能是将边或环向其他模型上进行圆锥和圆柱投影。
通过将边或环向其他模型投影的方式即可得到开头图片所示的效果。
PDF Version: OpenCASCADE BRep Projection
