Also, for anyone who cares about this stuff, it looks like the National Geospatial-Intelligence Agency has made the sight reduction tables for Marine (HO 229) and Air (HO 249) Navigation available on their Maritime Safety website once again. They had them down to the public for a while, perhaps to keep evildoers from being able to figure out where they are.
Now, if anyone knows where to find historical charts, I'd be deeply appreciative.
Thanks,
Walter
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I found some errors in the on line version of H.O. 249 and called it to their attention. I believe they have corrected the errors not. Below is my correspondence with Office of Global Navigation/Technology
National Geospatial-Intelligence Agency
Gary LaPook
--------------------------------------------------
November 13, 2008
Tim Doherty
Office of Global Navigation/Technology
National Geospatial-Intelligence Agency
(301)227-1075
-----Original Message-----
From: Gary J. LaPook [mailto:garylapook@pacbell.net]
Sent: Thursday, November 13, 2008 7:11 AM
To: Doherty, Tim
Subject: Additional errors found in H.O 249
Dear Mr. Doherty,
Last year I called your attention to some errors I had found in the
on-line version of H.O. 249 for Hc's near zero and I checked recently
and these appear now to have been corrected. However, when I was
reviewing the updated version I found some additional errors.
In volume 2 page 158 is completely wrong and appears to be a duplicate
of page 152 and page 133 is also completely wrong and appears to be a
duplicate of page 139! I suspect that there are many other similar
errors hiding in this volume that my cursory review didn't reveal.
Gary LaPook
------------------------------------------------------------
March 24, 2009
Gary
Once again, I would like to thank you for discovering these errors and bringing them to our attention.
I am pleased to report that the on-line PDF files have recently been replaced with corrected versions. Since the generation software was no longer available to us, the errant pages had to be re-created manually, which was quite painstaking - almost as painful as actually finding the resources to do it!
Anyway, the world is now a safer place because of your diligence. Well done, sir!
Best regards,
Tim Doherty
Office of Global Navigation/Technology
National Geospatial-Intelligence Agency
(301)227-1075
-----Original Message-----
From: Gary J. LaPook [mailto:garylapook@pacbell.net]
Sent: Monday, November 17, 2008 7:45 AM
To: Doherty, Tim
Subject: Errors in H.O. 249
It would appear that editions before 1999 are O.K. but those after that date are suspect as is the online version. A quick check to make on your edition is to compare pages 152 and 158 and also 133 and 139, if these are duplicates you have the bad editions. Also look at page 148, LAT 24, DEC 27 same name, LHA 256 for an example of the lack of the negative sign type of error.
I have compared my 1970 edition volume 2 with the online version and the only pages that I have found that are incorrect are 133 and 158 and I will check volume 3 tonight. My methodology was to compare the Hc given on the first line of each page for DEC either 7 or 22, as appropriate, in the 1970 edition with the online version which should find any pages that are duplicates or containing many errors. Using the method I found several pages where there were the one minute types of discrepancies that I described before that I do not think shows an actual error in the online (newer editions) tables. These were on pages 47, 77, 134,179, and 235.
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I have now finished the comparison of my 1970 volume 3 with the online volume 3, using the same methodology described before, to determine if there were any pages duplicated in this volume and am happy to report that I found no duplicated pages. Nor did I find any other errors. I found 10 cases of the one minute difference discrepancy that I described before. I checked each of the discrepancies I found in both volumes 2 and 3 (there were 5 in volume 2) and found the same round off error as before. The actual Hc was never more than 3 seconds away from the 30 second dividing line for rounding off. For example, on page 134 LAT 22, DEC 7 contrary name, LHA 69 the Hc in the 1970 edition is 16º 31' while in the online edition it is 16º 30'. The computed Hc is 16º 30' 27.5"
just 2.5 seconds below the 30' round off dividing line and is correctly rounded down to 16º 30' in the online edition. For some reason the computer algorithm used in calculating the Hcs in the 1970 edition incorrectly rounded up to 16º 31'. This was the same pattern with all 15 cases that I checked, the online edition had the correct values and the 1970 edition differed by one minute due to this systemic rounding off error.
I am attaching pages 133, 139 152, and 158 from the online edition, two copies of each, one copy downloaded in November 2007 and the second copy downloaded today. By comparing them you will see that 133 is a duplicate of 139 and 158 is a duplicate of 152 and this error has not yet been corrected. Also by comparing both copies of page 133 you will see an example of the missing minus sign type error e.g. LAT 22, DEC 0, LHA 91 in the 2007 copy that has been eliminated in the 2008 copy.
I have also scanned and attached pages 133 and 158 from my 1970 edition that you can print and place in your copy of volume 2 to use instead of the ones you have that are duplicates of 139 and 152.
Gary LaPook
Author
Topic: "Astronomical Methods in Aerial Navigation" NACA #198 (Read 18597 times)
