OGRDataSource *AoIIntersection::intersectAoIWithLayers ( OGRDataSource *ogrSourceData, OGRPolygon *aoiPoly, IntersectionSummary *summary, const char *outFmt )
{
OGRDataSource *ogrIntersection = NULL;
// Spatial reference setup
// make a spatial reference for the area of interest polygon
OGRSpatialReference aoiRef;
aoiRef.SetWellKnownGeogCS( "WGS84" );
// make a spatial reference for the coord sys we will use to calculate area in acres - Albers USA equal area conic
bool acreageCalcAvailable = true;
char *aecWkt = "PROJCS[\"USA_Contiguous_Lambert_Conformal_Conic\",GEOGCS[\"GCS_North_American_1983\",DATUM[\"North_American_Datum_1983\",SPHEROID[\"GRS_1980\",6378137,298.257222101]],PRIMEM[\"Greenwich\",0],UNIT[\"Degree\",0.017453292519943295]],PROJECTION[\"Lambert_Conformal_Conic_2SP\"],PARAMETER[\"False_Easting\",0],PARAMETER[\"False_Northing\",0],PARAMETER[\"Central_Meridian\",-96],PARAMETER[\"Standard_Parallel_1\",33],PARAMETER[\"Standard_Parallel_2\",45],PARAMETER[\"Latitude_Of_Origin\",39],UNIT[\"Meter\",1],AUTHORITY[\"EPSG\",\"102004\"]]";
OGRSpatialReference aecRef;
OGRErr ogrErr = aecRef.importFromWkt( &aecWkt );
if ( ogrErr != OGRERR_NONE )
{
setError ( NO_SPATIAL_REFERENCE );
acreageCalcAvailable = false;
}
// begin creating the output data structure
// OGRDataSource is the root
ogrIntersection = buildIntersectionDataSource( outFmt );
if (! ogrIntersection )
{
setError( NO_OUTPUT_DATASOURCE );
return 0;
}
int acreIndex = 0, areaIndex = 0;
OGRFieldDefn *acreFldDefn = NULL, *areaPctFldDefn = NULL;
OGRFeatureDefn *featureDefn = buildFeatureDefinition( acreIndex, areaIndex, acreFldDefn, areaPctFldDefn );
// walk the layers in the input data
//
OGRLayer *inputLayer;
summary->numLayers = ogrSourceData->GetLayerCount();
for (int layerCt = 0; layerCt < summary->numLayers; ++layerCt)
{
inputLayer = ogrSourceData->GetLayer( layerCt );
if ( inputLayer == NULL )
{
setError( NO_INPUT_LAYER );
// clean up
delete ogrIntersection;
return 0;
}
// make a clone of aoi polygon to be manipulated
OGRPolygon *aoiClone = (OGRPolygon *)aoiPoly->clone();
if ( ! aoiClone )
{
setError( NO_AOI_CLONE );
// clean up
delete ogrIntersection;
return 0;
}
// ensure that the area of interest polygon is in the same spatial reference as the data layer
// find the spatial reference for the layer
OGRSpatialReference *dataRef = inputLayer->GetSpatialRef();
if ( dataRef )
{
OGRCoordinateTransformation *aoiTransform = OGRCreateCoordinateTransformation( &aoiRef, dataRef );
if( aoiTransform == NULL )
{
setError( NO_AOI_TRANSFORM );
// clean up
delete ogrIntersection;
delete aoiClone;
return 0;
}
aoiClone->transform( aoiTransform );
delete aoiTransform;
}
// find the transform from data layer's CS to Albers USA
// for acreage calculation
OGRCoordinateTransformation *aecTransform = NULL;
acreageCalcAvailable = false;
if ( dataRef )
{
aecTransform = OGRCreateCoordinateTransformation( dataRef, &aecRef );
if( aecTransform == NULL )
{
setError( NO_ACRE_TRANSFORM );
}
else
acreageCalcAvailable = true;
}
// the area enclosed by the AoI
// used for computing the percentage of the AoI intersected by polygons
summary->aoiArea = aoiClone->getExteriorRing()->get_Area();
// create a layer for outputting the intersecting polygons
OGRLayer *intersectionLayer = ogrIntersection->CreateLayer( inputLayer->GetLayerDefn()->GetName(), dataRef, wkbPolygon, 0 );
if ( ! intersectionLayer )
{
setError( NO_OUTPUT_LAYER );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
return 0;
}
// add fields to layer
ogrErr = intersectionLayer->CreateField( acreFldDefn );
if ( ogrErr != OGRERR_NONE )
{
setError( NO_ACRE_FIELD );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
return 0;
}
ogrErr = intersectionLayer->CreateField( areaPctFldDefn );
if ( ogrErr != OGRERR_NONE )
{
setError( NO_AREA_FIELD );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
return 0;
}
// march through the geometry in the layer seeking overlap with area of interest
//
inputLayer->ResetReading();
OGRFeature *inputFeature;
while( (inputFeature = inputLayer->GetNextFeature()) != NULL )
{
// get the geometry part of the feature
OGRGeometry *inputGeometry = inputFeature->GetGeometryRef();
// test for polygon type - the only type we read
if( inputGeometry != NULL
&& wkbFlatten(inputGeometry->getGeometryType()) == wkbPolygon )
{
OGRPolygon *inputPolygon = (OGRPolygon *) inputGeometry;
++summary->totalInputPolyCt;
double inputPolyArea = inputPolygon->get_Area();
summary->totalInputPolyArea += inputPolyArea;
// here's the important test - does this polygon intersect our area of interest?
if (aoiClone->Intersects( inputGeometry ))
{
// generate a polygon that represents the intersection of the polygon with the AoI
OGRGeometry *intersectionGeometry = aoiClone->Intersection( inputGeometry );
if ( intersectionGeometry && wkbFlatten(intersectionGeometry->getGeometryType()) == wkbPolygon )
{
double intersectionArea = ((OGRPolygon *)intersectionGeometry)->get_Area();
summary->totalIntersectionArea += intersectionArea;
++summary->intersectionCt;
if (intersectionArea < inputPolyArea)
++summary->partEnclosedCt;
// create a feature with feature definition, add geometry to it and add it to our layer
OGRFeature *intersectionFeature = new OGRFeature( featureDefn );
if (! intersectionFeature )
{
setError( NO_OUTPUT_FEATURE );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
return 0;
}
intersectionFeature->SetGeometry( intersectionGeometry );
double percentOfAoI = intersectionArea / summary->aoiArea;
intersectionFeature->SetField( areaIndex, percentOfAoI);
summary->totalPercentOfAoI += percentOfAoI;
if ( acreageCalcAvailable )
{
OGRGeometry *intersectionCopy = intersectionGeometry->clone();
if ( intersectionCopy )
{
ogrErr = intersectionCopy->transform( aecTransform );
if ( ogrErr != OGRERR_NONE )
{
setError( NO_ACRE_TRANSFORMATION );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
delete intersectionCopy;
return 0;
}
// get area in known metric CS
double intersectionAcreage = ((OGRPolygon *)intersectionCopy)->get_Area();
// convert sq m to acres
double MetersToFt = 3.28084;
double SqFtPerAcre = 43560.0;
intersectionAcreage *= ((MetersToFt * MetersToFt) / SqFtPerAcre);
intersectionFeature->SetField( acreIndex, intersectionAcreage );
summary->totalIntersectionAcres += intersectionAcreage;
delete intersectionCopy;
}
else
{
setError( NO_ACRE_OBJECT );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
return 0;
}
}
intersectionLayer->CreateFeature( intersectionFeature );
if ( ogrErr != OGRERR_NONE )
{
setError( NO_FEATURE_ADDED );
// clean up
delete ogrIntersection;
delete aoiClone;
delete aecTransform;
return 0;
}
}
else
{
}
}
}
else
{
printf( "no polygon geometry\n" );
}
OGRFeature::DestroyFeature( inputFeature );
}
delete aoiClone;
delete aecTransform;
}
return ogrIntersection;
}
