5.9.2 example(metarials-cpp) just this src provided by installing qt-opensource-windows-x86-5.9.2.exe.. this is my computer path C:\Qt\Qt5.9.2\Examples\Qt-5.9.2\qt3d\materials-cpp. and my os is window 8.1 Microsoft Windows [Version 6.3.9600] ..
2.using vtk to load a stl file it will cost more twice memery than file size. and our file maybe very large . but using qt3d even not getting rid of the repeat points, it cost less memery than vtk. excepert drawing some axise and grid .(consist of lines adn cubics)
3 btw could u tell how to get rid of the repeat points..this my snippet:
Qt3DRender::QGeometry geometry = new Qt3DRender::QGeometry;
auto m_positionAttr = new Qt3DRender::QAttribute(geometry);
//auto m_colorAttr = new Qt3DRender::QAttribute(geometry);
auto m_indexAttr = new Qt3DRender::QAttribute(geometry);
auto m_NORAttr = new Qt3DRender::QAttribute(geometry);
auto m_positionBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, geometry);
//auto m_colorBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, geometry);
auto m_indexBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::IndexBuffer, geometry);
auto m_NORBuffer = new Qt3DRender::QBuffer(Qt3DRender::QBuffer::VertexBuffer, geometry);
uint vsize = amesh.mVertices.size();
uint isize = amesh.mIndices.size();
vsize = isize;
//Configure the attributes access
QByteArray colorData;
uint size1 = sizeof(QVector3D);
//positionData.resize(vsize * 3 * sizeof(float));
QByteArray mNormals, mindexs;
charpdata = (char*)&amesh.mVertices[0][0];
mindexs.resize(vsize * sizeof(uint));
uintpindexs = (uint)mindexs.data();
for (uint i = 0; i <vsize; i++)
pindexs[i] = i;
const uint nVerts = vsize;
const uint size = nVerts * 3 * sizeof(float);
QByteArray positionBytes, noramlbytes;
//positionBytes.resize(size);
vsize = nVerts;
uint facenum = vsize / 3;
uint j = 0, i = 0;
mNormals.resize(vsize * 2 * sizeof(Vector3));
uintpindex1 = &amesh.mIndices[0];
Vector3vertex = &amesh.mVertices[0];
Vector3pnormal = (Vector3)mNormals.data();
Vector3 n;
FindMinMax((QVector3D*)vertex, amesh.mVertices.size());
movetocenterbyOC((QVector3D*)vertex, amesh.mVertices.size(), mcenter);
uint cnt = 0, index1 = 0, count = 0;
Vector3 pt[3] = {};
for (j = 0; j <vsize * 2; )
{
if (j % 6 == 0) {
pt[0] = vertex[pindex1[cnt]];
pt[1] = vertex[pindex1[cnt+1]];
pt[2] = vertex[pindex1[cnt+2]];
CalcNormal(pt, n);
}

	pnormal[j++] = vertex[pindex1[cnt++]];
	pnormal[j++] = n;
}
//	m_indexBuffer->setData(mindexs);
m_NORBuffer->setData(mNormals);
//m_positionBuffer->setData(QByteArray::fromRawData((char*)&vertex[0], size)); 
const quint32 elementSize = 3 + 3;
const quint32 stride = elementSize * sizeof(float);
//m_colorBuffer->setData(colorData);
m_positionAttr->setName(Qt3DRender::QAttribute::defaultPositionAttributeName());
m_positionAttr->setVertexBaseType(Qt3DRender::QAttribute::Float);
m_positionAttr->setDataSize(3);
m_positionAttr->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
m_positionAttr->setBuffer(m_NORBuffer);
m_positionAttr->setCount(vsize);
m_positionAttr->setByteStride(stride);
//m_positionAttr->setProperty();

m_NORAttr->setName(Qt3DRender::QAttribute::defaultNormalAttributeName());
m_NORAttr->setVertexBaseType(Qt3DRender::QAttribute::Float);
m_NORAttr->setDataSize(3);
m_NORAttr->setAttributeType(Qt3DRender::QAttribute::VertexAttribute);
m_NORAttr->setBuffer(m_NORBuffer);
m_NORAttr->setCount(vsize);
m_NORAttr->setByteOffset(3 * sizeof(float));
m_NORAttr->setByteStride(stride);


geometry->addAttribute(m_positionAttr);
geometry->addAttribute(m_NORAttr);
//  geometry->addAttribute(m_indexAttr);
geometry->setParent(m3dentity);
return geometry;