Comments on: Datum Transformations – Converting Coordinates from NAD27 to NAD83

By: Bob Bywater

Bob Bywater — Sat, 07 Oct 2023 13:27:53 +0000

The Meades Ranch coordinates were FIXED at 39° 13′ 26.686″ north latitude and 98° 32′ 30.506″ west longitude. The site became a key marker for the US surveys. I cannot find however. any document which provides the details and methods used in determining those choices for the coordinates, especially any about fixing the longitude.

Speculation: I presume the longitude value was derived through timing intervals between astronomical transits viewed in London and at one (or more) US Observatory. The Dov at the Airy Transit Circle location has as its consequence, that now one should regard the WGS84 meridian as the effective meridian for the Airy telescope for transiting timing purposes. That is, the interval in timing between US and those from London should be considered as coming from a slightly greater longitudinal separation (than just from the Airy meridian itself). Of course, the intervals between the timings of transits in London and US also depended on their operators “personal equations” (Bessel).
Are there any documents extant, concerning the deliberations behind the adoption and the reasons how (earlier) and the final (fixed) Meades Ranch longitude was obtained?

By: Dave Cameron

Dave Cameron — Mon, 03 Feb 2020 05:24:55 +0000

Map Tools was a great little app and I used it quite a bit, especially for datum transforms. So convenient!!! Sad to see it disappear. I suspect the group that originated the app got bought out or has disbanded.

By: Lee

Lee — Tue, 28 May 2019 13:59:36 +0000

I once had an app on my iPhone called Map Tools which was a datum transformation tool. It was a purchased app but recently failed to update. I had previously found that it sometimes had to be deleted, reloaded to work. I work offshore and don’t always have a good internet connection with which to update my apps so I do that from good WiFi before departure. Having failed to recently update I delete them attempted to download again. But now I can’t find it when I search within my apps. Has anyone else used this app and experienced the same thing? I wonder if the developer of this app has folded andit’s no longer available. Can anyone recommend a good app for multiple datum transformations?

By: Richard Dean

Richard Dean — Wed, 10 Jan 2018 14:00:11 +0000

But where can I find the origin alignment, axis rotation, and scale information that will allow me to relate Clarke 1866, GRS80, and WGS84?