desimeter

Introduction

This package contains scripts and data for coordinates transformations in DESI. It's all in python, and runs on a laptop.

It comprises

• spots detection (based on a 2D FFT convolution of the input FVC image by Gaussian).
• spots centroid (simultaneous chi2 fit of the amplitude and position of a Gaussian integrated in the pixels).
• spots match to existing fiducials.
• fit of transformation from FVC pixels to focal plane X Y coordinates.
• metrology data, with all the routines to convert the engineering data in DocDB to the files used to fit the transformation, including a patch that corrects for missing or erroneous metrology, see py/desimeter/data/README.rst for more information on this.
• matching positioner spots based upon their expected locations.
• sky transformations (precession, aberration, refraction, polar mis-alignment)
• fit of GFA guide stars to adjust telescope pointing, field rotation while absorbing a scaling factor (potentially accounting for thermal dilatation)
• prediction of fiber sky RA,Dec coordinates

See desimeter/doc/coordinates.rst for a definition of the coordinate systems.

Automated build & testing

Script Examples

These examples use a fiber view camera (FVC) image taken during PSF stability tests, available at NERSC at:

/global/project/projectdirs/desi/cmx/psfstability/thetaphi-20191113/data/fvc/fvc.20191113120837.fits

They also work on FVC images written by ICS as part of platemaker acquisition sequences by using the images in the F0000, F0001, etc FITS extensions.

Here is an example fitting FVC spots and matching to fiducials:

desi_fvc_proc -i fvc.20191113120837.fits  -o spots.csv

Plot of the residuals with respect to the metrology:

plot_fvc_residuals -i out.csv

Plot of the metrology data

plot_metrology

Fit of guide stars (at KPNO), saving the transformation in a json file

desi_fit_guide_star_coordinates -i /n/home/datasystems/users/ameisner/reduced/realtime/20200119/00042312/gfa-00042312_catalog.fits --fits-header /exposures/desi/20200119/00042312/gfa-00042312.fits.fz -o fp-00042312.json

Then using it to predict the fiber RA,Dec from a FVC image

desi_fvc_proc -i /exposures/desi/20200119/00042311/fvc-00042311.fits.fz --field-model fp-00042312.json --expected /exposures/desi/20200119/00042311/coordinates-00042311.fits -o fvc-00042311.csv

Code examples

Detect spots and match fiducials:

import fitsio
from desimeter.detectspots import detectspots
from desimeter.findfiducials import findfiducials
image = fitsio.read('fvc.20191113120837.fits')

#- Detects spots: XPIX, YPIX, XERR, YERR, COUNTS
spots = detectspots(image)
print(spots.colnames)

#- matches to fiducials and adds LOCATION and PINHOLE_ID columns
spots = findfiducials(spots)
print(spots.colnames)
spots.write('spots.csv', overwrite=True)

Load spots and fit a FVC -> FP transform:

from astropy.table import Table
from desimeter.transform import fvc2fp
spots = Table.read('spots.csv')

#- Fit transform; adds X_FP, Y_FP, X_FP_METRO, Y_FP_METRO columns
tx = fvc2fp.fit(spots, update_spots=True)
print(spots.colnames)

Check consistency with fiducial metrology (PINHOLE_ID>0):

ii = spots['PINHOLE_ID'] > 0
dr2 = (spots['X_FP'] - spots['X_FP_METRO'])**2 + \
     (spots['Y_FP'] - spots['Y_FP'])**2
rms = np.sqrt(np.mean(dr2[ii]))
print('1D RMS = {:.1f} um'.format(1000*rms))

Save that transform for later use:

tx.write_jsonfile('fvc2fp.json')

Read it back in and do transforms between FVC and FP:

t2 = fvc2fp.read_jsonfile('fvc2fp.json')

import numpy as np
xpix, ypix = np.random.uniform(1000,5000, size=(2,50))
xfp, yfp = t2.fvc2fp(xpix, ypix)

xpix2, ypix2 = t2.fp2fvc(xfp, yfp)
dr = np.sqrt((xpix2-xpix)**2 + (ypix2-ypix)**2)
print(np.median(dr))

Dependencies

desimeter requires numpy, scipy, astropy, fitsio, and matplotlib.

Python 3.6 or greater is required.

It purposefully does not require desiutil, desimodel, or any other offline desidata packages to facilitate integration with the DESI online environment and to minimize getting started overhead for non-desidata users.

Similarly, it does not use the ICS ops database or any online code to facilitate offline development and studies, e.g. on a laptop.

Installation

Get a copy of the code:

git clone https://github.com/desihub/desimeter

If you want to use desimeter but don't intend to actively develop it:

cd desimeter
python setup.py install

For developers, we recommend adding desimeter/py to $PYTHONPATH and desimeter/bin to $PATH instead of installing desimeter.

To cause desimeter to use alternate metrology data (e.g., the spare petal1 rather than the petals at KPNO), set an environment variable like DESIMETER_DATA=<yourpath>/desimeter/py/desimeter/data/lbl-petal1

For developers in a Windows + Anaconda environment, add a new user variable PYTHONPATH in the Environment Variables GUI editor. Include the path (for your machine) ending in desimeter\py in the Value field. (Note: after an admittedly non-exhaustive search, no obvious equivalent was found for adding desimeterbin to Path. You'll have to type out python <full path to command> at the Anaconda Prompt terminal.)

Other Notes

desimeter is a work in progress and we expect that class names and module organization will change.