Lattice Expression Language


The Lattice Expression Language (LEL) makes it possible to do arithmetic on lattices (in particular on images [which are just lattices plus coordinates]) in AIPS++. An expression can be seen as a lattice (or image) in itself. It can be used in any operation where a normal image is used.

To summarize, the following functionality is supported:

  • The common mathematical, comparison, and relational operators.
  • An extensive list of mathematical and logical functions.
  • Mixed data type arithmetic and automatic data type promotion.
  • Support of image masks.
  • Masking using boolean expressions.
  • Handling of masks in an expression.
  • Support of image regions.
  • Interface from both Glish and C++.

The first section explains the syntax. The last sections show the interface to LEL using Glish or C++. The Glish interface makes it possible to embed Glish variables and expressions in a LEL command. At the end some examples are given. If you like, you can go straight to the examples and hopefully immediately be able to do some basic things.

LEL operates on lattices, which are a generalization of arrays. As said above a particular type of lattice is an image; they will be used most often. Because lattices can be very large and usually reside on disk, an expression is only evaluated when a chunk of its data is requested. This is similar to reading only the requested chunk of data from a disk file.

LEL is quite efficient and can therefore be used well in C++ and glish code. Note however, that it can never be as efficient as carefully constructed C++ code.

Note 216 gives a detailed description how LEL is implemented using various C++ classes.

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