Using Multiple Masks

Today I made some changes to the way that MAKEMAP handles masks for the AST, FLT and COM models. Previously, only one mask could be used with each model. So for instance if the following configuration was used:

ast.zero_mask = 1
ast.zero_lowhits = 0.1

the AST.ZERO_MASK setting would take precedence over the AST.ZERO_LOWHITS setting, resulting in the external mask supplied via the REF parameter being used, and the AST.ZERO_LOWHITS setting ignored.

The current behaviour is now to combine such masks together. So in the above example the external mask and the lowhits mask would be combined to create a single mask. The combination is done in a manner determined by the AST.ZERO_UNION parameter. If this parameter is true (i.e. non-zero), a pixel in the combined mask is considered a "source" pixel if it is flagged as a source pixel in any of the individual masks (i.e. the combined source area is the union of the individual source areas). If AST.ZERO_UNION is false (i.e. zero) , a pixel in the combined mask is considered a "source" pixel if it is flagged as a source pixel in all of the individual masks (i.e. the combined source area is the intersection of the individual source areas). The default for AST.ZERO_UNION is 1 - that is, the union of the masks is used by default.

In addition, a different external masks can now  be used with each model. This is achieved by using a new syntax for the XXX.ZERO_MASK configuration parameters. Each of these configuration parameters can now be given the name of the ADAM parameter which is to be used to get the corresponding mask. [Just to remind you, "ADAM" parameters are different to configuration parameters - all the configuration parameters are obtained using a single ADAM parameter called CONFIG.] External masks can be specified using any of the ADAM parameters "REF", "MASK2" and "MASK3" ("REF" serves the purpose of "MASK1"). The REF parameter has been around for a long time, but the MASK2 and MASK3 parameters are new.

So for instance, to  use different external masks for the AST and FLT models, you could do:

ast.zero_mask = REF
flt.zero_mask = MASK2

and then run makemap as

% makemap ref=ast_mask.sdf mask2=flt_mask.sdf

Or to use the same mask for both models, you should do:


ast.zero_mask = REF
flt.zero_mask = REF

% makemap ref=mask.sdf


The old XXX.ZERO_MASK syntax is still supported. Supplying a positive integer value causes the mask to be accessed using the REF parameter, as before. The default for each XXX.ZERO_MASK parameter is still zero, meaning that no external mask is used.

One twist to beware of with the new scheme, is that the REF parameter is treated somewhat differently to the MASK2 and MASK3 parameters. The REF parameter is still used, as it always has been, to define the pixel grid of the output map. This means that any mask supplied via the REF parameter will, by definition, be aligned with the output map. The same is not true of the MASK2 and MASK3 parameters. If using these parameters, you must ensure that the mask NDFs are aligned in pixel coordinates with the output map. The easiest way to do this is to create your mask from the output map of a previous similar run of makemap.