On the Transform method, the last two parameters
are densification tolerance and a geotransformation object. These are
optional, which is why in VB you don't need to pass them. Unfortunately, in
C++, "optional" parameters are needed and are passed in a VARIANT
structure. If you look at the C++ wrapper files found in: \..\Samples\MFC\Common, and in:
MoProjCoordSys.cpp, you'll see the Transform function declared
as:
LPDISPATCH
CMoProjCoordSys::Transform(LPDISPATCH
FromCoordSys,
LPDISPATCH
FromShape,
const VARIANT&
DensificationTolerance,
const VARIANT& GeoTransformation)
So, you'll need to set up two extra VARIANTs.
Here's some code to put within the OnMouseMove event handler that demonstrates
this.
NB. I recommend that if you are switching in
between datums then you do use geotransformation objects in all your projection
work.
void
CYourApplicationDlg::OnMouseMoveMap(short Button, short Shift, long X, long Y)
{
// Here, we'll
demonstrate the Transform method whilst tracking
// the mouse coordinates
in the debug window. We're assuming that our mapcontrol
// has
already been set to project to UTM Grid Zone 33N.
CMoPoint
aPoint(m_map.ToMapPoint((float)X, (float)Y));
TRACE2( "Projected mouse
position %f\t%f\n", aPoint.GetX(), aPoint.GetY() );
// define a Projected
Coordinate System - or just get it from the
mapcontrol!
CMoProjCoordSys
aProjCoordSys;
aProjCoordSys.CreateDispatch(TEXT("MapObjects2.ProjCoordSys"));
aProjCoordSys.SetType(moProjCS_WGS1984UTM_33N);
// define a
geographic coordsys
CMoGeoCoordSys
aGeogCoordSys;
aGeogCoordSys.CreateDispatch(TEXT("MapObjects2.GeoCoordSys"));
aGeogCoordSys.SetType(moGeoCS_WGS1984);
// create VARIANTs to
be used for the transform method
// Note. If you did want to use the
geotrans, the Variant should be
// set up to accept dispatch
pointers:
// e.g. va.vt = VT_DISPATCH; and then va.pdispVal =
myGeotrans.m_lpDispatch;
VARIANT va; // for the
geotransformation object
VariantInit(&va);
va.vt =
VT_NULL;
VARIANT vax; // for
the densification tolerance - this should be passing a
double
VariantInit(&vax);
vax.vt = VT_R8;
vax.dblVal =
0.0;
// Now transform the
point
CMoPoint
aGeogPoint(aGeogCoordSys.Transform(aProjCoordSys.m_lpDispatch,
aPoint.m_lpDispatch, vax, va));
TRACE2( "Geographic mouse position
%f\t%f\n", aGeogPoint.GetX(), aGeogPoint.GetY() );
// and do some
rubbish collection to recover
memory
aProjCoordSys.ReleaseDispatch();
aGeogCoordSys.ReleaseDispatch();