Slice.h

Classes

Slice -- define a (start,length,increment) along an axis (full description)

class Slice

Interface

Public Members

Slice()

Slice(Int Start, uInt Length=1, uInt Inc=1)

Bool all() const

Int start() const

uInt length() const

uInt inc() const

Int end() const

Description

Synopsis

A "slice" (aka Section) is a a regular sub-Array (and ultimately sub-Image) that is defined by defining a (start,length,increment) for each axis in the array. That is, the output array's axis is of size "length", and the elements are sampled by stepping along the input array in strides of "increment".

The "length" is the length of the OUTPUT array, the output length is NOT divided by the increment/stride.

If increment is not defined, then it defaults to one. (Increment, if defined, must be >= 1). If length is not defined, then it defaults to a length of one also (i.e. just the pixel "start"). If start is also undefined, then all pixels along this axis are chosen. This class deprecates the "_" (IndexRange) class, which had a failed syntax and used (start,end,increment) which is generally less convenient. Some simple examples follow:

    Vector<Int> vi(100);          // Vector of length 100;
    //...
                                  // Copy odd values onto even values
    vi(Slice(0,50,2)) = vi(Slice(1,50,2));
    
    Matrix<float> mf(100,50), smallMf;
    smallMf.reference(mf(Slice(0,10,10), Slice(0,5,10)));
                                  // smallMF is now a "dezoomed" (every 10th pix)
                                  // refference to mf. Of course we could also
                                  // make it a copy by using assignment; e.g:
    
    smallMf.resize(0,0);          // Make it so it will "size to fit"
    smallMf = mf(Slice(0,10,10), Slice(0,5,10));

As shown above, normally Slices will normally be used as temporaries, but they may also be put into variables if desired (the default copy constructors and assignment operators suffice for this class).

While it will be unusual for a user to want this, a zero-length slice is allowable.

Another way to produce a slice from any of the Array classes is to use SomeArray(blc,trc,inc) where blc,trc,inc are IPositions. This is described in the documentation for Array.

Member Description

Slice()

The entire range of indices on the axis is desired.

Slice(Int Start, uInt Length=1, uInt Inc=1)

Create a Slice with a given start, length, and increment. The latter two default to one if not given.

Bool all() const

Was the entire range of indices on this axis selected?

Int start() const

Report the selected starting position. If all() is true, start=len=inc=0 is set.

uInt length() const

Report the defined length. If all() is true, start=len=inc=0 is set.

uInt inc() const

Report the defined increment. If all() is true, start=len=inc=0 is set.

Int end() const

Attempt to report the last element of the slice. If all() is True, end() returns -1 (which is less than start(), which returns zero in that case).