Map Feature Attributes

Each map feature can also have attributes. If the map feature is a town, its attributes can be its name, or the number of inhabitants. Attributes can be used, for example, for graphical rendering. In the section Creating a Colored Line Renderer the color of polylines representing contour lines on a map is defined by the elevation attribute.

Attributes belong to the class IlvFeatureAttribute. They are stored in the following two classes:

• IlvFeatureAttributeInfo, which defines the attribute properties, such as name, type, mandatory, or optional characters.

• IlvFeatureAttributeProperty, which contains the values of these attributes.

The following code sample lists the attributes of an IlvMapFeature object and displays them on the screen.

void

dumpAttributes(const IlvMapFeature* feature)

{

const IlvFeatureAttributeProperty* attributes =

feature->getAttributes();

if(!attributes)

return;

const IlvFeatureAttributeInfo* info =

attributes->getInfo();

 

if(info) {

IlvUInt count;

 

count = info->getAttributesCount();

for(IlvUInt i = 0; i < count; i++) {

 

const char* name = info->getAttributeName(i);

 

const IlvMapClassInfo* clsinfo = info->getAttributeClass(i);

const IlvFeatureAttribute* fa = attributes->getAttribute(i);

if(clsinfo->isSubtypeOf(IlvStringAttribute::ClassInfo())) {

const char *str = ((IlvStringAttribute*)fa)->getValue();

IlvPrint("%s %s", name ? name : "", str ? str : "");

} else if(clsinfo->isSubtypeOf(IlvIntegerAttribute::ClassInfo())){

int in = ((IlvIntegerAttribute*)fa)->getValue();

IlvPrint("%s %d", name ? name : "", in);

} else if(clsinfo->isSubtypeOf(IlvDoubleAttribute::ClassInfo())){

double dbl = ((IlvDoubleAttribute*)fa)->getValue();

IlvPrint("%s %g", name ? name : "", dbl);

} else if(clsinfo->isSubtypeOf(IlvBooleanAttribute::ClassInfo())){

IlvBoolean bo = ((IlvBooleanAttribute*)fa)->getValue();

IlvPrint("%s %s", name ? name : "",

bo ? "true" : "false");

}

}

}

}

 

The attributes are of different types, according to whether they represent whole numbers, floating-point values, character strings, and so on. The predefined attributes, all of the IlvFeatureAttribute class, are in the attribute package.