astAddRegion

Add a Region into a Moc

Description:

This function modifies a Moc by combining it with a supplied Region. The Region must be defined within a SkyFrame, or within a CmpFrame that contains a SkyFrame. The Region will be converted to ICRS before being combined with the Moc. The way in which they are combined is determined by the " cmode" parameter.

Note, since Moc is a subclass of Region this method can be used to add a Moc into another Moc. In such cases, the data is transferred from one Moc to another directly. For other classes of Region an adaptive algorithm is used to find the HEALPix cells that are inside the Region. An initial grid, corresponding to the HEALPix cells at the order given by the Moc s " MinOrder" attribute, is placed over the bounding box of the supplied Region. Each of these cells is tested at 9 positions (corners, edge-centres and cell-centre). If all 9 positions are inside the supplied Region, then the whole cell is assumed to be inside the Region. If no positions are inside the supplied Region, then the whole cell is assumed to be outside the Region. If there is a mix of inside and outside positions, the cell is divided into four sub-cells at HEALPix order " MinOrder+1" , and the same test is applied to each sub-cell in turn. When the HEALPix order reaches the value of the Moc s " MaxOrder" attribute, each cell is tested only at the cell centre, and is assumed to be inside the Region if the cell centre is in the Region.

This process means that contiguous " islands" or " holes" in the supplied region may be missed if they are smaller than the cell size associated with HEALPix order " MinOrder" .

Synopsis

void astAddRegion( AstMoc this, int cmode, AstRegion region )

Parameters:

this
Pointer to the Moc to be modified.
cmode
Indicates how the Moc and Region are to be combined. Any of the following values may be supplied:
  • AST__AND: The modified Moc is the intersection of the original Moc and the Region.

  • AST__OR: The modified Moc is the union of the original Moc and the Region.

  • AST__XOR: The modified Moc is the exclusive disjunction of the original Moc and the Region.

region
Pointer to the Region to be combined with the Moc.

Notes: