Judy May wrote: > This may be affecting me. Being a backwoods orienteering buff in > the U.S., I use a map datum of NAD27 CONUS. My GPS receiver is set to > work in that datum, also. > > I have noticed a greater positional error that should occur when > using my Meade LX200 telescope. (Sometimes by a factor of ten minutes > of arc) > > Kevin commented on converting one datum to another. Can someone > tell me the necessary formulas to go from NAD27 CONUS to the two WGS > datums? Try the National Imagery and Mapping Agency website at: http://www.nima.mil/ Of particular interest is their document: NIMA TR8350.2 DEPARTMENT OF DEFENSE WORLD GEODETIC SYSTEM 1984 Its Definition and Relationships with Local Geodetic Systems However, its all a bit tricky. You might find the DOS program MADTRAN somewhere which does the conversions for various datums (data? :-) to/from WGS-84. I got it from the NIMA site a while back (I think it was still the Defense Mapping Agency then) but it doesn't seem to be publicly available anymore. The MADTRAN source code (it was published in some sort of Basic) is a reasonable reference on how to do basic transformations between datums. But, if your really need to use a particular datum, why not just switch your GPS to WGS-84 or whatever you want while you survey the location of your telescope? > > And lastly, what datum would we expect automated "go-to" telescopes > would have been engineered with? I am not so sure Meade would > understand what I was asking if I called them. I don't think the telescope would care about the datum. The lat/long would only be used to give a first approximation to the orientation in space of the telescope's axes. The effects of alignment errors on the mounting would dominate any difference in datum. Except when observing near objects (the Moon or closer?) the actual position of the telescope is pretty much irrelevant. I assume the goto function of the telescope doesn't deal with the parallax for close objects anyway. Even the best alignment to local vertical will not help much as any datum is just an ellipsoid designed to give a reasonable approximation to the Earth's shape over a cetain area (the whole world in the case of WGS-84). The local vertical will probably be different anyway. The survey methods used to determine the actual local vertical are pretty much the same as aligning a telescope to reference stars, I think. Ed. ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Fri Aug 17 2001 - 11:05:17 PDT