FootprintFunctors

Demonstrate the use of FootprintFunctors to work with Footprints; the code's in footprintFunctor.cc.

Start by including needed headers and declaring namespace aliases

/* 
 * LSST Data Management System
 * Copyright 2008, 2009, 2010 LSST Corporation.
 * 
 * This product includes software developed by the
 * LSST Project (http://www.lsst.org/).
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 * This program is free software: you can redistribute it and/or modify
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
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#include <cstdio>

#include "lsst/afw/image.h"
#include "lsst/afw/detection.h"

namespace afwDetect = lsst::afw::detection;
namespace afwImage = lsst::afw::image;
namespace afwGeom = lsst::afw::geom;

We don't want our functor visible in the global namespace, or even outside this file, so put it in an anonymous namespace:

namespace {

Declare our functor FindSetBits, it's parameterised over MaskT, and provide a constructor. _bits is the accumulator for Mask bits in the Footprint

    template <typename MaskT>
    class FindSetBits : public afwDetect::FootprintFunctor<MaskT> {
    public:
        FindSetBits(MaskT const& mask       // The Mask the source lives in
                   ) : afwDetect::FootprintFunctor<MaskT>(mask), _bits(0) {}

Define what it means to apply the functor; in this case, OR together the bits

        // method called for each pixel by apply()
        void operator()(typename MaskT::xy_locator loc,        // locator pointing at the pixel
                        int,                                   // column-position of pixel
                        int                                    // row-position of pixel
                       ) {
            _bits |= *loc;
        }

Return the desired value

        // Return the bits set
        typename MaskT::Pixel getBits() const { return _bits; }

Clear the accumulator between Footprints

        // Clear the accumulator
        void reset() { _bits = 0; }

Define the private variable, _bits

        void reset(afwDetect::Footprint const&) { ; }
    private:
        typename MaskT::Pixel _bits;
    };

close our anonymous namespace

}

Now define a function, printBits, to exercise the FindSetBits. We'll pass it a Mask and a list of Footprints

void printBits(afwImage::Mask<afwImage::MaskPixel> mask,

Declare a FindSetBits, count, and tell it about our Mask

               afwDetect::FootprintSet::FootprintList const& feet) {
    FindSetBits<afwImage::Mask<afwImage::MaskPixel> > count(mask);

Loop over all our Footprints

    for (afwDetect::FootprintSet::FootprintList::const_iterator fiter = feet.begin();

Clear the bitmask and OR together all the bits under the footprint (*fiter is a Footprint::Ptr, so **fiter is a Footprint)

        fiter != feet.end(); ++fiter) {
        count.apply(**fiter);

Print the result

        printf("0x%x\n", count.getBits());
    }
}

Just to show you this in action, let's make a MaskedImage and check its bits

int main() {
    afwImage::MaskedImage<float> mimage(afwGeom::Extent2I(20, 30));

    (*mimage.getImage())(5, 6) = 100;
    (*mimage.getImage())(5, 7) = 110;

    *mimage.getMask() = 0x1;
    (*mimage.getMask())(5, 6) |= 0x2;
    (*mimage.getMask())(5, 7) |= 0x4;

    afwDetect::FootprintSet ds(mimage, 10);

    printBits(*mimage.getMask(), *ds.getFootprints());
}

Running the example should print 0x7.