As described in the main page of this document, we manually construct a file containing the positions of several detectors in the IHMP system of the fplane.txt file (in units of arcseconds) and in the acm camra system (in units of acm pixles).

% cat Data.ALL
# IHMP-acm positions after Sep2018 FPA take-down
# name     X,Y_ihmp         X,Y_acm      X,Y_acm _prev
# data
555       0.7  -73.1     455.0  398.7    455.0  398.7
600     -39.9   9.97     148.7  250.3    148.7  250.3
056     -50.0 -150.0     738.6  211.6    738.6  211.6
066      50.0 -150.0     739.7  577.3    739.7  577.3

In Oct2018 we began splitting shuffle's handling of the rotation angle representing the acm and ihmp on the sky. We needed a direct way to check the acm position of the IHMP without knowing thses angles and I came up with the following simple approach. I include the note I sent to MS and GH about this.

Matt and Gary:
 I realized that my determination of X,Y_ihmp of last night is based on the 
old ihmp x,y data (including Joe Ninan's 600,610 estimates). It occurred to 
me that we can do a simple graphical derivation: 

 1) Compute the radius from the IHMP center to BIB, LRS2-R, LRS2-B 
    using the coordinate Gary sent a couple days ago. 
 2) Convert these radii in arcsec to units of acm pixels using ps=0.2709 "/pix 
 3) Use Steven J's acm X,Y to make a ds9 regions file and overplot on an acm image. 
 4) Find where the circles intersect. This gives the IHMP center in acm pixles. 

 acm plate scale = 0.2709 "/pix 
 RAD = radius in acm pixels to the IHMP center 
 
                       From Gary H:
      SJ acm X,Y       X,Y_ihmp (arcsec)    X,Y_ihmp (acm pix)       RAD
     ------------      -----------------  ---------------------- 
056  735.4  212.6       -50.0  -150.0       -184.6   -553.7         583.7
066  737.9  581.7       -50.0  +150.0       -184.6   +553.7         583.7
555  453.0  401.5         0.0   72.456         0.0    267.6         267.6

Using the above acm cooridinates and radii I make the ds9 regions files
I make acm_fiducials.reg:
% cat acm_fiducials.reg
# Region file format: DS9 version 4.1
# Filename: 20180402T092129.0_acm_sci_proc.fits
image
circle(735.4,212.6,583.7) # color=blue width=3 font="helvetica 20 normal roman" text={LRS2-B}
circle(737.9,581.7,583.7) # color=red width=3 font="helvetica 20 normal roman" text={LRS2-R}
circle(453.0,401.5,267.6) # color=cyan width=3 font="helvetica 20 normal roman" text={BIB}

I find for the X,Y_IHMP:        X,Y_ihmp = 183.6 399.8 

See the attached figs. Recall the two values we had before:

MS values: 
acam_x_origin = 183.0
acam_y_origin = 400.7

My values: 
acam_x_origin = 184.0 -+ 0.9 acm pixels
acam_y_origin = 384.5 -+ 0.8 acm pixels 

So, Matt's values agrees very well with this check.  

-Steve 

The BIB, LRS2-B and LRS2-R positions plotted with circles having radii equal to their offsets in units of acm pixels. A random acm image is used to overplot these positions using ds9. By zooming in on this view we can find the intersection of these three circles and hence measure directly an estimate of the location of the IHMP center on the acm for Oct2018 (a couple weeks after the Oct2018 FPA takedown). Below I show the ds9 regions file used to make this figure: % cat acm_fiducials.reg # Region file format: DS9 version 4.1 # Filename: 20180402T092129.0_acm_sci_proc.fits image circle(735.4,212.6,583.7) # color=blue width=3 font="helvetica 20 normal roman" text={LRS2-B} circle(737.9,581.7,583.7) # color=red width=3 font="helvetica 20 normal roman" text={LRS2-R} circle(453.0,401.5,267.6) # color=cyan width=3 font="helvetica 20 normal roman" text={BIB}

A zoomed-in view of the figure above. The black circle represents a graphical dtermination of the acm position of the IHMP center. I derive: IHMP Center Estimate: X,Y_ihmp = 183.6 399.8 (acm pixels)

In the first figure (acm+ihmp_fig1.png): 
I use acm_lrs2_view to get LRS2-B,R region files
 * Now we see that the acm Y axis runs in the direction of IHMP (and tracker) X.
 * Positive X_ihmp is towards the LRS2-R direction (or larger acm Y). 
 * Positive Y_ihmp is towards lower Xacm values (to the left). (Recall that 
   the LRS2 ifu lonong axes lie along tracker X at Yihmp=-150.) 

You can see even in the above figure, that to have the BIB circle agree with the 
LRS2-R and LRS2-B circles we'd have to shift it to the LEFT in the acm image. This 
means we would be moving the BIB cnter towards +Yihmp. The amonut of the shift
I measure (see acm+ihmp_fig2.png) is all in acm X:  
   BIB dX = 453.0 - 450.3 = 2.7 acm pixels  = 0.73" in the +Yihmp direction 

Note: In the figure the shifted BIB circle is plotted as the thinner line with 
      a center to the left (more +Yihmp) of the original BIB position. 

Hence, since our old BIB (X,Y)_ihmp = 0.0,-72.5, then our implied revised BIB 
center in the IHMP system would  
      BIB (X,Y)_ihmp =  0.0 , -69.8 (arcseconds) 

The BIB, LRS2-B and LRS2-R positions plotted with circles having radii equal to their offsets in units of acm pixels. I have added a legend that indicated the IHMP directions.

The original BIB circle (thick cyan line) has been shifted in the -Xacm frame to better agree with the LRS2-B and LRS2-R circles. The new position (thin cyan line) has been used to derive a revised BIB ihmp position of (X,Y)ihmp = 0.0 , -69.8.