Jump to content


Photo

Where to get accurate Longitude and Latitude?

  • Please log in to reply
33 replies to this topic

#1 EdmontonAB

EdmontonAB

    Apollo

  • *****
  • Posts: 1275
  • Joined: 30 Apr 2008
  • Loc: Sooke, BC , Canada

Posted 03 December 2012 - 03:27 AM

Now that I have an observatory, I need to find my correct long and lat. I have looked at Google Earth and CalSky, but they give me different values. Can anyone tell me where I could get the most accurate figures? Thanks,

#2 Christopher Erickson

Christopher Erickson

    Vanguard

  • *****
  • Moderators
  • Posts: 2273
  • Joined: 08 May 2006
  • Loc: Waikoloa Village, Hawaii

Posted 03 December 2012 - 04:08 AM

Most (not all) GPS's will display your precise Lat/Lon coordinates to the nearest ten meters/yards or so.

Secondly, from Google Earth.

Be advised that just because they differ, it doesn't mean that one of them is wrong. There are a number of different coordinate representation systems that have been developed to solve various cartographical problems over the years and advanced GPS's actually allow you to pick between them.

http://www.gmat.unsw...fs/coorddef.pdf

Just a point to consider if you plan to publish your precise coordinates on the Internet. Do you really want to give the whole world the precise coordinates of all of your precious and expensive gear? I would suggest instead that you round or truncate those coordinates to the nearest ten kilometers/miles, more or less.

And for the most part (except if you have a modern Meade GOTO mount and you want to track satellites) GOTO scopes don't need nearly that kind of precision to function correctly. Usually a 500-kilometer/300-mile radius is more than sufficient for the initial alignment of the average GOTO scope.

I hope this helps.

#3 rick-SeMI

rick-SeMI

    Mariner 2

  • -----
  • Posts: 232
  • Joined: 08 Jan 2011
  • Loc: Michigan - USA

Posted 03 December 2012 - 05:45 AM

This isn't bad

http://www.worldatla...tude_finder.htm

Or you can use this. Enter city/state or zip and watch the lat and lon change as you move the cursor over the map

http://mapserver.myt...FTOKEN=61523820

Or maybe this one. Pick a spot on the left and watch the coordinates change at the top of the map.

http://earthexplorer.usgs.gov/

I have a hand-held GPS unit (Garmen) that is really acurate...

My wife got me a GPS for the car. It was OK locally but "tried" to take us way out of the way on our visit to my
step-son in Fayetteville, NC. He is stationed at Ft Bragg.
When I got home I but it back in its box and may cannibilize it for it's parts :(

#4 Aquarist

Aquarist

    Apollo

  • -----
  • Posts: 1041
  • Joined: 27 Aug 2012
  • Loc: Illinois

Posted 03 December 2012 - 08:40 AM

I got mine from Google earth and confirmed with a Garmin GPS. Not exactly synchronized, but close enough.

#5 Mike I. Jones

Mike I. Jones

    Gemini

  • *****
  • Posts: 3257
  • Joined: 02 Jul 2006
  • Loc: Fort Worth TX

Posted 03 December 2012 - 09:20 AM

Agree - Great point on not telling the world where your toys are to 3 meter accuracy!
Mike

#6 Doug Culbertson

Doug Culbertson

    Skylab

  • *****
  • Posts: 4257
  • Joined: 06 Jan 2005

Posted 03 December 2012 - 09:28 AM

I use an Android app called GPS Status on my HTC phone. GPS coordinates and a compass all in one app.

#7 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 03 December 2012 - 10:10 AM

Android/Iphone is probably the most accurate. Google Earth is good enough to 'bomb' on :D.

#8 csa/montana

csa/montana

    Den Mama

  • *****
  • Posts: 86525
  • Joined: 14 May 2005
  • Loc: montana

Posted 03 December 2012 - 11:24 AM

Just a point to consider if you plan to publish your precise coordinates on the Internet. Do you really want to give the whole world the precise coordinates of all of your precious and expensive gear? I would suggest instead that you round or truncate those coordinates to the nearest ten kilometers/miles, more or less.



Very good point, Chris.

#9 simpleisbetter

simpleisbetter

    Surveyor 1

  • *****
  • Posts: 1848
  • Joined: 18 Apr 2011

Posted 03 December 2012 - 11:35 AM

My current favorite method is the GPS in my cell phone, which usually pretty much agrees with Google Earth. Out of curiosity, I just compared my main site on both Google Earth and CalSky (satellite view) and they're both virtually the same; not exact, but coords within meters of each other.

Google Earth and my cell phone GPS both have the added benefit of showing my altitude, used by my observing software when building sites.

#10 raf1

raf1

    Viking 1

  • *****
  • Posts: 991
  • Joined: 18 Nov 2005
  • Loc: south Texas

Posted 03 December 2012 - 12:27 PM

Just a point to consider if you plan to publish your precise coordinates on the Internet. Do you really want to give the whole world the precise coordinates of all of your precious and expensive gear? I would suggest instead that you round or truncate those coordinates to the nearest ten kilometers/miles, more or less.



Very good point, Chris.


May also want to rethink listing your equipment in case anyone is out there "shopping" for astro goodies. Personally, I don't list my equipment just to keep the laughing and cat calls at a minimum but some of the equipment lists I have seen here are very impressive! CS, Ron

#11 EdmontonAB

EdmontonAB

    Apollo

  • *****
  • Posts: 1275
  • Joined: 30 Apr 2008
  • Loc: Sooke, BC , Canada

Posted 03 December 2012 - 03:02 PM

I am not planning on putting up my coordinates. I just want to get accurate ones for transits and occultations. Thanks for the sites.

#12 Christopher Erickson

Christopher Erickson

    Vanguard

  • *****
  • Moderators
  • Posts: 2273
  • Joined: 08 May 2006
  • Loc: Waikoloa Village, Hawaii

Posted 03 December 2012 - 06:24 PM

I am not planning on putting up my coordinates. I just want to get accurate ones for transits and occultations. Thanks for the sites.


Then I hope that the information I provided will help!

Transits and occultations are indeed cool. I have participated in a number of Pluto occultations with scientists from SwRI and the Lowell Observatory and they were fascinating, not to mention riddled with almost white-knuckled suspense!

Attached Files



#13 Mary B

Mary B

    Vendor - Echo Astronomy and Electronics

  • *****
  • Vendors
  • Posts: 3072
  • Joined: 21 May 2010
  • Loc: Minnesota

Posted 03 December 2012 - 06:56 PM

I use a program called Smart Compass on my cell phone.

#14 raf1

raf1

    Viking 1

  • *****
  • Posts: 991
  • Joined: 18 Nov 2005
  • Loc: south Texas

Posted 03 December 2012 - 08:34 PM

No worries Steve - that was sort of a throw down admonition for the general good. As Chris said, you're going to have great fun timing occultations. Good luck! CS, Ron

#15 Starhawk

Starhawk

    Space Ranger

  • *****
  • Posts: 5614
  • Joined: 16 Sep 2008
  • Loc: Tucson, Arizona

Posted 04 December 2012 - 12:04 AM

Commander compass lite oh my iPhone works very well for this- even off the grid.

-Rich

#16 Christopher Erickson

Christopher Erickson

    Vanguard

  • *****
  • Moderators
  • Posts: 2273
  • Joined: 08 May 2006
  • Loc: Waikoloa Village, Hawaii

Posted 04 December 2012 - 12:20 AM

I think a lot of people are missing the point of the original question, which was why there are subtle discrepancies between two different coordinate determination tools. The OP is NOT looking for another basic coordinate determination tool like a GPS or GPS-enabled smartphone.

And going back to the original question, and now knowing that it is related to precise calculations for occultation and transit data collection, I would say that the most important step would be making sure that everyone participating in the occultation or transit event is using the same coordinate determination tool with the same cartographic compensation settings. After all it is the deltas between stations that are most important, as opposed to absolute cartographical position.

I hope this helps.

#17 Calypte

Calypte

    Apollo

  • -----
  • Posts: 1169
  • Joined: 20 Mar 2007
  • Loc: Anza, California

Posted 04 December 2012 - 12:46 AM

As another poster has pointed out, you don't need to be very accurate for go-tos. Anything within, say, 50 miles is easily good enough for that purpose. But if you're like me, you want to know your coordinates to the millimeter, if you can achieve it. It's just my thing. I got my coordinates from several tries with a GPS receiver. Latitude and longitude within a few meters are easy to derive, but accurate elevation is another matter. It may require repeated tries, each time letting the receiver sit undisturbed for many minutes, to let it settle to an almost-steady value. You may have to average the results. Even then, you may be off by several meters. Many years ago I inquired with the International Occultation Timing Association about possibly timing a particular grazing occultation (the Moon occulting Spica), since I happened to live right on the path and could observe it from my backyard. This was before the dithering of satellite signals was discontinued, and you could only get GPS coordinates within a couple of hundred feet. IOTA didn't consider that good enough, and they also wanted elevation accurate enough to allow for the height of the observing equipment off the ground. I was told to get coordinates and elevation from topo maps. This procedure assumed that whatever I would do with a ruler on a map would be within the then-current accuracy of a GPS receiver (1994). My neighborhood of the time had been graded by machines a couple of years earlier, and no extant map had elevation accurate to the requested precision. Even if I were on an undeveloped site, it all assumed that the map(s), likely surveyed decades earlier, were accurate to within a few inches. I was skeptical. I observed the occultation visually, watching Spica wink in and out of the mountains on the Moon's limb, but I never again considered timings.

#18 Al8236

Al8236

    Apollo

  • *****
  • Posts: 1129
  • Joined: 18 Aug 2010
  • Loc: 48.9173N 122.1390W

Posted 04 December 2012 - 05:08 AM

As far as the coordinates that I list for my observatory, I use the location of the local Sheriff sub-station that is X mi.from me,
See I'm not even going to give a search radius to work from!
But Google earth has been more than adequate for alignment purposes.

#19 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 04 December 2012 - 06:13 AM

GPS is accurate to within about a house with commercial receivers. If you're looking for better than what your i-phone can provide you, you're going to need survey-grade equipment that give you a 'more accurate' elevation figure.

GPS is very accurate. We regularily steer munitions through windows using it.

#20 Mary B

Mary B

    Vendor - Echo Astronomy and Electronics

  • *****
  • Vendors
  • Posts: 3072
  • Joined: 21 May 2010
  • Loc: Minnesota

Posted 05 December 2012 - 08:12 PM

Smart Compass must average the elevation because it is rock solid and doesn't change on my Droid 3

#21 mich_al

mich_al

    Vanguard

  • *****
  • Posts: 2467
  • Joined: 10 May 2009
  • Loc: Rural central lower Michigan Yellow Skies

Posted 05 December 2012 - 08:53 PM

I think a lot of people are missing the point of the original question,


That's sure not unique to this thread. :foreheadslap: Sometime ya gotta wonder what question it is they're answering. :question:

#22 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 06 December 2012 - 08:11 AM

GPS is the most accurate way to find your location in lattiude and longitude. It also is the best way to ensure everyone is on the same geo-coordinate plane between disparate locations since you have a common reference time.

Here is another link from a website explaining what makes GPS accurate. I especially like that it explains you the importance of ephemeris and atmospheric effects into the equation:
http://earthmeasurem...S_accuracy.html

Great article from the WI DNR on GPS accuracy in relation to hunting:

http://dnr.wi.gov/ma...ps_accuracy.pdf

The last article povides a very detailed analysis of how their testing was conducted. Well worth reading.

Without survey grade equipment, you're not going to beat the accuracy of your average cell phone.

Enjoy!

#23 Bob Griffiths

Bob Griffiths

    Getting Grouchy

  • *****
  • Posts: 10674
  • Joined: 10 Oct 2005
  • Loc: Frederick Maryland

Posted 06 December 2012 - 10:29 AM

I use an Android app called GPS Status on my HTC phone. GPS coordinates and a compass all in one app.


Works like a charm ... plus shows your elevation and offset from mag North

AND ITS FREE....

Thanks Doug I download it the other day after reading your post
:bow:
Bob G.

#24 Doug Culbertson

Doug Culbertson

    Skylab

  • *****
  • Posts: 4257
  • Joined: 06 Jan 2005

Posted 06 December 2012 - 12:29 PM

Can't beat free! Glad to be of service, Bob.

#25 EddWen

EddWen

    Apollo

  • -----
  • Posts: 1097
  • Joined: 26 Apr 2008

Posted 06 December 2012 - 01:25 PM

I'm curious; what is the accuracy of an average cell phone?

My Garmins (with WAAS) frequently report 1 meter accuracy.


Without survey grade equipment, you're not going to beat the accuracy of your average cell phone.

Enjoy!








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics