Weighting different observations in makemake and skyloop

Both makemap and skyloop can be used to produce maps from multiple overlapping observations. Up to now, it has not been possible to control the weights used for each observation when forming the total co-added map. Instead, fixed weights equal to the reciprocal of each pixel variance were used. The new CHUNKWEIGHT configuration parameter can now be used to specify a weight for each observation. The weights determined from the pixel variances are multiplied by these user-specified weights, which default to unity.

The weights can be specified in two ways:

1. The CHUNKWEIGHT configuration parameter can be set to an arbitrary algebraic expression in which the variable names are the names of FITS keywords. The keywords must exist in the input data and have numerical values. The expression should be enclosed in double quotes. As an example, you could include this line in your configuration file:
   
      chunkweight = "AMSTART * WVMTAUST"

The values of the FITS keywords are read from the observation header and substituted into the expression to get the weight to use for the observation.


2. A comma-separated list of explicit numerical weights can be supplied, enclosed in parentheses. If insufficient values are given in the list, the last value is replicated as often as is necessary.
   
      chunkweight = (1.0,2.0,3.0)