[SIM2D-126] Work around unphysical detectorMap features

Mon, 4 Jan 2021 20:23:23 +0000

The detectorMaps coming from the simulator have non-physical features at either end, possibly due to spline artifacts. Here is a plot of the residual after removing a constant dispersion (wavelength change per pixel) as a function of detector row for one of the central fibers of the m arm, showing the problem:

Jim Gunn says, "There is nothing physical which could cause this." We suspect the problem is in the splining of the optical model in the simulator. A workaround is to drop the second, third, third-to-last and second-to-last knots for the wavelength solution from the detectorMap, e.g.:

import numpy as np
from pfs.drp.stella import SplinedDetectorMap
detMap = SplinedDetectorMap.readFits("/home/pfs/pfs/drp_pfs_data/detectorMap/detectorMap-sim-m1.fits")
def selectArray(array):
    result = np.empty(len(array) - 4, dtype=np.float32)
    result[0] = array[0]
    result[-1] = array[-1]
    result[1:-1] = array[3:-3]
    return result

SplinedDetectorMap(detMap.bbox, detMap.fiberId, [detMap.getXCenterSpline(ff).getX() for ff in detMap.fiberId], [detMap.getXCenterSpline(ff).getY() for ff in detMap.fiberId], [selectArray(detMap.getWavelengthSpline(ff).getX()) for ff in detMap.fiberId], [selectArray(detMap.getWavelengthSpline(ff).getY()) for ff in detMap.fiberId], detMap.getSpatialOffsets(), detMap.getSpectralOffsets(), detMap.visitInfo, detMap.getMetadata()).writeFits("detectorMap-simhack-m1.fits")

This ticket will implement this workaround in the simulator.

PFS-JIRA

[SIM2D-126] Work around unphysical detectorMap features