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Photogrammetry

The original GBT photogrammetry was performed with the telescope at the rigging angle of 50.29 degrees. The whole dish could not be seen at once from the camera's position on the crane, so the dish was rotated in azimuth and overlapping photos were obtained. The purpose was to verify that all actuators were within +/-1/4 inch from of the best-fit paraboloidal surface, with the focal length constrained to f=60 meters exactly. 97% of the actuators were within that tolerance. The results are given in the attached file. Of the 2209 actuator targets, 23 were found to be in excess of 3/8 of an inch (0.375" = 9525 microns) away from the target value. (These 23 are listed at the bottom of this page.) The contractor was required to bring these into the +/-0.375" (9525 microns) specification by adjusting them mechanically, but they were never remeasured by photogrammetry. (We believe the adjustment was done by installing shims, but we will confirm this with Harry Morton. It could have been done by sliding them along the slotted grooves, unless the total groove travel was exhausted.) Most of the offending actuators are located on the lower right edge of the dish (as viewed from the receiver cabin). This figure shows the location of the 23 outliers from this viewpoint (by circled numbers). The offset values for these actuators listed in the current actuator zero file assume that the error was completely removed by the mechanical adjustment, but this may not be the case. To investigate this issue, we have examined the traditional holography from Oct 2003 through April 2004. We have estimated the remaining actuator error for each of these 23 actuators, and plotted the results here. Red is the photogrammetry value, green is the holography value, and the y-axis is in microns.

We find that for almost all of the actuators on the edge of the dish (marked with an 'E' in the 16Oct2003 plot), the remaining actuator error is not zero but is close to the maximum allowed error (1, 5, 6, 11, 12, 13, 14, 15, 18, 19, 21). For the actuators that are located a few panels inward from the edge of the dish (1, 2, 4, 7, 8, 9, 20), the error appears to have been reduced to a value closer to zero, perhaps because someone told them that these were more important (as the receiver illumination pattern is greater on those panels).

Outliers

# Node Spreadsheet code Photos Modifications
1 609043 50 1.jpg 2.jpg 3.jpg no shim
2 611042 86 1.jpg 2.jpg 3.jpg shim = 0.75"
3 620042 77 1.jpg 2.jpg 3.jpg no shim
4 636009 2004 1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg weld broken and lowered?
5 643530 753 1.jpg 2.jpg 3.jpg no shim, weld intact
6 645028 874 1.jpg 2.jpg 3.jpg 2 shims stacked to 0.75" (1/2+1/4)
7 646024 1138 1.jpg 2.jpg 3.jpg shim = 0.75"
8 650020 1359 1.jpg 2.jpg 3.jpg shim ~ 0.75"
9 650021 1301 1.jpg 2.jpg shim ~ 0.75"
10 650025 1084 1.jpg 2.jpg 3.jpg shim ~ 0.75"
11 652021 1300 1.jpg 2.jpg 3.jpg shim ~ 0.75"
12 652023 1189 1.jpg 2.jpg 3.jpg 4.jpg shim ~ 0.75"
13 654021 1299 1.jpg 2.jpg 3.jpg shim ~ 0.75"
14 656018 1475 1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6.jpg 7.jpg shim = 0.95"
15 656019 1415 1.jpg 2.jpg 3.jpg shim ~ 0.95"
16 656020 1356 1.jpg 2.jpg 3.jpg shim = 0.75"
17 658018 1474 1.jpg 2.jpg 3.jpg shim = 0.95"
18 658019 1414 1.jpg 2.jpg 3.jpg shim ~ 0.95"
19 658020 1355 1.jpg 2.jpg 6 shims stacked to 0.7"
20 660010 1963 1.jpg 2.jpg 3.jpg 4.jpg 5.jpg 6 shims stacked to 0.7"
21 660017 1535 1.jpg 2.jpg 3.jpg 4.jpg shim = 0.95"
22 660018 1473 1.jpg 2.jpg 3.jpg 4.jpg shim = 0.95"
23 662016 1597 1.jpg 2.jpg 3.jpg shim = 0.95"

Comparison shots of 660009 = 1.jpg 2.jpg 3.jpg

Shots of 658016 = 1.jpg 2.jpg 3.jpg 4.jpg (shim = 0.4")

Shim thicknesses estimated by tape measure and digital photos.

-- ToddHunter and FredSchwab - 19 Jun 2008

Attachment: sort Action: Size: Date: Who: Comment:
gbtphotogrammetry.txt action 172738 19 Jun 2008 - 22:02 ToddHunter photogrammetry table (file dated July 5, 2000)
locationOfOffenders.pdf action 31339 19 Jun 2008 - 22:07 ToddHunter location of the 23 outliers on the dish
offenders_16oct2003.pdf action 135847 19 Jun 2008 - 22:18 ToddHunter Estimated actuator error from 16Oct2003 holography
offenders_02apr2004.pdf action 136290 19 Jun 2008 - 22:18 ToddHunter Estimated actuator error from 02Apr2004 holography
telescopes-1395.jpg action 66364 19 Jun 2008 - 22:38 ToddHunter photo of actuator installed on telescope
09360_001.JPG action 355212 23 Jun 2008 - 22:54 ToddHunter  
09360_002.JPG action 334240 23 Jun 2008 - 22:55 ToddHunter  
09360_003.JPG action 347744 23 Jun 2008 - 22:56 ToddHunter  
09360_004.JPG action 412678 23 Jun 2008 - 22:56 ToddHunter  
09360_005.JPG action 425280 23 Jun 2008 - 22:56 ToddHunter  
09360_006.JPG action 366428 23 Jun 2008 - 22:56 ToddHunter  
09600_001.JPG action 361256 23 Jun 2008 - 23:00 ToddHunter  
09600_002.JPG action 360166 23 Jun 2008 - 23:00 ToddHunter  
09600_003.JPG action 343736 23 Jun 2008 - 23:00 ToddHunter  
10600_001.JPG action 364332 23 Jun 2008 - 23:02 ToddHunter  
10600_002.JPG action 334654 23 Jun 2008 - 23:02 ToddHunter  
10600_003.JPG action 367180 23 Jun 2008 - 23:03 ToddHunter  
10600_004.JPG action 390958 23 Jun 2008 - 23:03 ToddHunter  
10600_005.JPG action 355924 23 Jun 2008 - 23:03 ToddHunter  
16580_001.JPG action 451310 23 Jun 2008 - 23:06 ToddHunter  
16580_002.JPG action 361704 23 Jun 2008 - 23:06 ToddHunter  
16580_003.JPG action 355224 23 Jun 2008 - 23:06 ToddHunter  
16580_004.JPG action 360714 23 Jun 2008 - 23:06 ToddHunter  
17600_001.JPG action 297796 23 Jun 2008 - 23:10 ToddHunter  
17600_002.JPG action 315524 23 Jun 2008 - 23:10 ToddHunter  
17600_003.JPG action 329056 23 Jun 2008 - 23:11 ToddHunter  
17600_004.JPG action 297114 23 Jun 2008 - 23:11 ToddHunter  
18560_001.JPG action 308846 23 Jun 2008 - 23:13 ToddHunter  
18560_002.JPG action 331988 23 Jun 2008 - 23:14 ToddHunter  
18560_003.JPG action 361148 23 Jun 2008 - 23:14 ToddHunter  
18560_004.JPG action 369122 23 Jun 2008 - 23:14 ToddHunter  
18560_005.JPG action 344876 23 Jun 2008 - 23:14 ToddHunter  
18560_006.JPG action 299354 23 Jun 2008 - 23:14 ToddHunter  
18560_007.JPG action 310450 23 Jun 2008 - 23:14 ToddHunter  
18580_001.JPG action 372922 23 Jun 2008 - 23:17 ToddHunter  
18580_002.JPG action 422786 23 Jun 2008 - 23:17 ToddHunter  
18580_003.JPG action 422194 23 Jun 2008 - 23:17 ToddHunter  
18600_001.JPG action 321006 23 Jun 2008 - 23:19 ToddHunter  
18600_002.JPG action 344594 23 Jun 2008 - 23:19 ToddHunter  
18600_003.JPG action 333770 23 Jun 2008 - 23:20 ToddHunter  
18600_004.JPG action 351910 23 Jun 2008 - 23:20 ToddHunter  
16620_001.JPG action 355192 02 Jul 2008 - 22:11 ToddHunter  
16620_002.JPG action 380132 02 Jul 2008 - 22:11 ToddHunter  
16620_003.JPG action 434106 02 Jul 2008 - 22:12 ToddHunter  
19560_001.JPG action 319410 02 Jul 2008 - 22:16 ToddHunter  
19560_002.JPG action 316734 02 Jul 2008 - 22:16 ToddHunter  
19560_003.JPG action 297756 02 Jul 2008 - 22:16 ToddHunter  
19580_001.JPG action 1258984 02 Jul 2008 - 22:19 ToddHunter  
19580_002.JPG action 849384 02 Jul 2008 - 22:19 ToddHunter  
19580_003.JPG action 1199592 02 Jul 2008 - 22:19 ToddHunter  
20500_001.JPG action 1199948 02 Jul 2008 - 22:23 ToddHunter  
20500_002.JPG action 952868 02 Jul 2008 - 22:23 ToddHunter  
20500_003.JPG action 956216 02 Jul 2008 - 22:23 ToddHunter  
20560_001.JPG action 330064 02 Jul 2008 - 22:26 ToddHunter  
20560_002.JPG action 293380 02 Jul 2008 - 22:26 ToddHunter  
20560_003.JPG action 284442 02 Jul 2008 - 22:26 ToddHunter  
20580_001.JPG action 222088 02 Jul 2008 - 22:30 ToddHunter  
20580_002.JPG action 233554 02 Jul 2008 - 22:30 ToddHunter  
21500_001.JPG action 811776 02 Jul 2008 - 22:33 ToddHunter  
21500_002.JPG action 879232 02 Jul 2008 - 22:33 ToddHunter  
21520_001.JPG action 862980 02 Jul 2008 - 22:36 ToddHunter  
21520_002.JPG action 1191400 02 Jul 2008 - 22:36 ToddHunter  
21520_003.JPG action 1130984 02 Jul 2008 - 22:37 ToddHunter  
21540_001.JPG action 277300 02 Jul 2008 - 22:39 ToddHunter  
21540_002.JPG action 322258 02 Jul 2008 - 22:39 ToddHunter  
21540_003.JPG action 398696 02 Jul 2008 - 22:39 ToddHunter  
23520_001.JPG action 1245660 02 Jul 2008 - 22:42 ToddHunter  
23520_002.JPG action 1154988 02 Jul 2008 - 22:42 ToddHunter  
23520_003.JPG action 1119068 02 Jul 2008 - 22:42 ToddHunter  
23520_004.JPG action 1145256 02 Jul 2008 - 22:42 ToddHunter  
24460_001.JPG action 277278 02 Jul 2008 - 22:45 ToddHunter  
24460_002.JPG action 426790 02 Jul 2008 - 22:45 ToddHunter  
24460_003.JPG action 369794 02 Jul 2008 - 22:45 ToddHunter  
25500_001.JPG action 1257644 02 Jul 2008 - 22:48 ToddHunter  
25500_002.JPG action 1048992 02 Jul 2008 - 22:48 ToddHunter  
25500_003.JPG action 1070368 02 Jul 2008 - 22:48 ToddHunter  
28450_001.JPG action 275646 02 Jul 2008 - 22:54 ToddHunter  
28450_002.JPG action 406964 02 Jul 2008 - 22:55 ToddHunter  
28450_003.JPG action 438534 02 Jul 2008 - 22:55 ToddHunter  
30435_001.JPG action 380272 02 Jul 2008 - 22:59 ToddHunter  
30435_002.JPG action 381616 02 Jul 2008 - 23:00 ToddHunter  
30435_003.JPG action 369452 02 Jul 2008 - 23:00 ToddHunter  
42110_001.JPG action 386782 08 Jul 2008 - 22:58 ToddHunter  
42110_002.JPG action 445126 08 Jul 2008 - 22:58 ToddHunter  
42110_003.JPG action 389504 08 Jul 2008 - 22:58 ToddHunter  
42200_001.JPG action 376726 08 Jul 2008 - 23:00 ToddHunter  
42200_002.JPG action 360656 08 Jul 2008 - 23:00 ToddHunter  
42200_003.JPG action 332364 08 Jul 2008 - 23:00 ToddHunter  
43090_001.JPG action 383248 08 Jul 2008 - 23:01 ToddHunter  
43090_002.JPG action 561240 08 Jul 2008 - 23:02 ToddHunter  
43090_003.JPG action 340070 08 Jul 2008 - 23:02 ToddHunter  

Topic Photogrammetry . { Edit | Attach | Ref-By | Printable | Diffs | r1.11 | > | r1.10 | > | r1.9 | More }
Revision r1.11 - 27 Aug 2008 - 15:04 GMT - ToddHunter
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