PlateSystem adapted for KIDS
EV
8 June 2006 --- KK March 2008
Case B has a minimum overlap between adjacent fields. In itself this is
not a problem, as the OmegaCAM calibration plan forsees for each field
an independent photometric and astrometric
calibration. However, some overlap is desired as an extra cross
check on calibrations. Case B provides a few 100 pixels overlap with
1-3 dithers; and that is tight but just enough.
Here, we explore the possibility to adopt this scenario for a whole sky
PlateSystem. ( see Tiling
the Sky for OmegaCAM)
defs:
A field of fieldsize_ra* fieldsize_dec has a fieldcenter.
A 5 point dither points with respect to this fieldcenter has 2
times ++ and 2
times -- in steps ditherstep_dec
and ditherstep_ra.
In fact for a 5 point dither the transitions at the edges of the fields
will have number of frames
...... 5 5 6 7 7 7 7 6 5 5 ......... per ditherstep.
The central two 7 dither strips are composed of 3+ 4 and 4 +3
dithers of the two fieldcenters.
Thus these two strips have a minimum of 3 dithers per
fieldcenter, which is what we define the overlap.
This grid has the property:
seperation_fieldcenters
= fieldsize - 2 * ditherstep.
This means that without ditherstepping single fields overlap 2
dithersteps.
When designing a grid for a whole hemisphere this condition is
kept as a strict minimum.
In practice, several effects cause a larger overlap than this minimum:
- in RA and DEC: putting an integer number of fields in
a RA strip, and on the meridian
- in RA: the cos (delta_dec) term over the 1 degree fieldsize_dec, which is larger than 200 px
at dec <-45 at the top of
an image compared to the bottom..
- in RA and DEC:
when ADC is in, the scale at the focal plane changes from 0.2134 to
0.2149 arcsec/pixel, enlarging the fieldsize_ra from 1.01270 to
1.01982 degrees, and the fieldsize_dec from 1.0202 to
1.02738 degrees, which implies an extra overlap of 112 px in both
directions.
- In Dec: differential atmospheric refraction enlarges fieldsize_dec
Case B also has the property that the average separation between fields
in degrees is larger in Dec than in RA direction because of
the large horizontal gaps between the CCDs ( 100 px in Ra= ditherstep_RA, 374 px in Dec=
ditherstep_Dec).
For the two-lens corrector:
fieldsize_ra = 1.01270 degree
fieldsize_dec= 1.0202 degree
With these setttings PlateSystem instantiates a Grid::
The following table lists some properties for each of the dec strips:
requested overlap ra= 1.37 % requested overlap dec= 4.63 %
fieldsize dec = 1.0202 degrees, fieldsizera= 1.0127 degrees
achieved distance fieldcenters in dec: 0.967741935484 degrees
achieved overlap in dec: 5.42066666667 %
Version for parents of KIDS
sequence Dec number overlap-ra
[degrees] [min%] min[px] +top[px]
1 0.4839 361 1.6 248 2
2 1.4516 361 1.6 250 7
3 2.4194 361 1.6 257 12
4 3.3871 361 1.7 269 17
5 4.3548 361 1.8 285 22
6 5.3226 360 1.6 261 26
7 6.2903 360 1.8 286 31
8 7.2581 359 1.7 271 36
9 8.2258 358 1.6 260 41
10 9.1935 357 1.6 254 46
11 10.1613 356 1.6 253 50
12 11.1290 355 1.6 257 55
13 12.0968 354 1.7 265 60
14 13.0645 353 1.7 277 64
15 14.0323 351 1.6 249 69
16 15.0000 350 1.7 271 74
17 15.9677 348 1.6 251 78
18 16.9355 347 1.8 283 83
19 17.9032 345 1.7 272 88
20 18.8710 343 1.7 266 92
21 19.8387 341 1.7 265 97
22 20.8065 339 1.7 268 101
23 21.7742 337 1.7 276 106
24 22.7419 335 1.8 289 110
25 23.7097 332 1.6 258 115
26 24.6774 330 1.7 280 119
27 25.6452 327 1.6 257 123
28 26.6129 325 1.8 289 128
29 27.5806 322 1.7 276 132
30 28.5484 319 1.7 267 136
31 29.5161 316 1.6 263 140
32 30.4839 313 1.6 263 145
33 31.4516 310 1.7 268 149
34 32.4194 307 1.7 277 153
35 33.3871 304 1.8 292 157
36 34.3548 300 1.6 258 161
37 35.3226 297 1.8 282 165
38 36.2903 293 1.6 256 169
39 37.2581 290 1.8 290 172
40 38.2258 286 1.7 273 176
41 39.1935 282 1.6 260 180
42 40.1613 278 1.6 251 184
43 41.1290 275 1.9 306 187
44 42.0968 271 1.9 308 191
45 43.0645 266 1.6 253 195
46 44.0323 262 1.6 263 198
47 45.0000 258 1.7 278 201
48 45.9677 254 1.9 298 205
49 46.9355 249 1.6 259 208
50 47.9032 245 1.8 289 211
51 48.8710 240 1.6 258 215
52 49.8387 236 1.9 299 218
53 50.8065 231 1.7 275 221
54 51.7742 226 1.6 256 224
55 52.7419 222 2.0 314 227
56 53.7097 217 1.9 305 230
57 54.6774 212 1.9 299 232
58 55.6452 207 1.9 298 235
59 56.6129 202 1.9 302 238
60 57.5806 197 1.9 311 240
61 58.5484 192 2.0 325 243
62 59.5161 187 2.2 345 246
63 60.4839 181 1.8 280 248
64 61.4516 176 1.9 310 250
65 62.4194 171 2.2 345 253
66 63.3871 165 1.8 290 255
67 64.3548 160 2.1 337 257
68 65.3226 154 1.8 287 259
69 66.2903 149 2.2 347 261
70 67.2581 143 1.9 304 263
71 68.2258 138 2.4 380 265
72 69.1935 132 2.1 343 266
73 70.1613 126 1.9 309 268
74 71.1290 121 2.6 411 270
75 72.0968 115 2.4 387 271
76 73.0645 109 2.3 364 273
77 74.0323 103 2.2 344 274
78 75.0000 97 2.0 327 275
79 75.9677 91 1.9 312 276
80 76.9355 86 3.1 492 278
81 77.9032 80 3.1 497 279
82 78.8710 74 3.2 509 280
83 79.8387 68 3.3 528 280
84 80.8065 62 3.5 556 281
85 81.7742 56 3.7 595 282
86 82.7419 50 4.1 650 283
87 83.7097 44 4.5 725 283
88 84.6774 38 5.2 830 284
89 85.6452 32 6.1 983 284
90 86.6129 25 3.5 556 284
91 87.5806 19 4.6 733 285
92 88.5484 13 6.8 1093 285
93 89.5161 7 13.5 2162 285
PlateSystem: total number of fields= 21618