Step 3: Defining a New Projection

Maps > Map Projections > Creating a New Projection > Step 3: Defining a New Projection

This step explains how to add the accessor support for the specific parameters of a projection.

The complete code of this projection is in the files proj_step3.h and proj_step3.cpp.

Adding Accessor Support

Accessors provide run-time information about the parameters of a projection. They are generally used to build generic projection editors in map applications.

To add an accessor to a projection you must write a getter and a setter function for this parameter and add the accessor to the IlvProjectionClassInfo during the static initialization phase.

// The getter for the latitudeOfTrueScale accessor.

static void _getter(const IlvProjection* p, IlvValue& v)

{

Mercator* mercator = (Mercator*) p;

char buffer[12];

v = IlvMaps::RadianToDMS(buffer,

mercator->getLatitudeOfTrueScale(),

IlTrue);

}

// The setter for the latitudeOfTrueScale accessor.

static IlvBoolean _setter(IlvProjection* p, const IlvValue& v)

{

Mercator* mercator = (Mercator*) p;

IlvDouble value;

IlvMapsError error = IlvMaps::DMSToRadian(v, value);

if (error != IlvMaps::NoError())

return IlFalse;

mercator->setLatitudeOfTrueScale(value);

return IlTrue;

}

void

Mercator::InitClass()

{

_polarZoneError =

IlvMaps::CreateError("&MercatorPolarZoneError");

ClassInfo()->addAccessor(IlvGetSymbol("latitudeOfTrueScale"),

IlvValueStringType,

_getter,

_setter);

}

Version 5.8