Support loading and searching likelihood images

[stevenstetzler]

I am hoping to use the GPU implementation of shift and stack portion of the KBMOD code on a set of custom likelihood images.

Currently, the KBMOD search procedure involves loading images (from fits on disk or constructing a kbmod.search.ImageStack from a list of kbmod.search.LayeredImage by hand), followed by convolution with a point spread function (PSF), followed by a shift-and-stack algorithm that calculates the ratio of two "likelihood images" implemented as a psi and phi array to find a search candidate.

I have a new way to construct a likelihood image that involves more than PSF convolution, and I would like to provide the psi and phi arrays directly to KBMOD before running a search. The operations are: PSF convolution to create psi and phi, threshold based on the ratio of psi and phi and a given threshold value (i.e. single-epoch detection SNR), digitize pixels to 0 and 1 (detected or not), and finally perform sum-pooling (add all of the values in neighboring pixels) to decrease the resolution of the images.

I am playing around with the code, and creating setters for the Psi and Phi images as well as a function to write to the protected variable psiPhiGenerated seems to be working so far.

# src/kbmod/search/bindings.cpp
    py::class_<ks>(m, "stack_search")
...
            .def("set_psi_images", &ks::setPsiImages)
            .def("set_phi_images", &ks::setPhiImages)
            .def("set_psi_phi_generated", &ks::setPsiPhiGenerated)

# src/kbmod/search/KBMOSearch.cpp
void KBMOSearch::setPsiImages(std::vector<RawImage>& imgs) { 
    psiImages.clear();
    for (auto i : imgs) { 
        psiImages.push_back(i);
    }
}

void KBMOSearch::setPhiImages(std::vector<RawImage>& imgs) {
    phiImages.clear();
    for (auto i : imgs) { 
        phiImages.push_back(i);
    }
}

void KBMOSearch::setPsiPhiGenerated(bool generated) {
    psiPhiGenerated = generated;
}

# src/kbmod/search/KBMOSearch.h
class KBMOSearch {
public:
...
    void setPsiImages(std::vector<RawImage>&);
    void setPhiImages(std::vector<RawImage>&);
    void setPsiPhiGenerated(bool generated);

The kbmod.search.search function still relies on an image stack though, so it would be helpful to have a search function that doesn't rely on the image stack if supporting this functionality of searching custom likelihood images directly.

[jeremykubica]

The code right now depends on being able to compute the Psi and Phi components instead of the aggregated likelihood. I think we want to focus on that approach for now instead of redesigning the core search. Feel free to re-open if you think this is urgent.