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Equipment Discussions >> Observatories

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EdmontonAB
Pooh-Bah
*****

Reged: 04/30/08

Loc: Sooke, BC , Canada
Where to get accurate Longitude and Latitude?
      #5551467 - 12/03/12 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,

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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Where to get accurate Longitude and Latitude? new [Re: EdmontonAB]
      #5551499 - 12/03/12 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.edu.au/snap/gps/clynch_pdfs/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.


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rick-SeMI
sage


Reged: 01/08/11

Loc: Michigan - USA
Re: Where to get accurate Longitude and Latitude? new [Re: EdmontonAB]
      #5551539 - 12/03/12 05:45 AM

This isn't bad

http://www.worldatlas.com/aatlas/latitude_and_longitude_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.mytopo.com/homepage/index.cfm?CFID=7419108&CFTOKEN=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


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Aquarist
scholastic sledgehammer


Reged: 08/27/12

Loc: Illinois
Re: Where to get accurate Longitude and Latitude? new [Re: rick-SeMI]
      #5551658 - 12/03/12 08:40 AM

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

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Mike I. Jones
Post Laureate
*****

Reged: 07/02/06

Loc: Fort Worth TX
Re: Where to get accurate Longitude and Latitude? new [Re: Christopher Erickson]
      #5551711 - 12/03/12 09:20 AM

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


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Doug Culbertson
Post Laureate
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Reged: 01/06/05

Re: Where to get accurate Longitude and Latitude? new [Re: Mike I. Jones]
      #5551718 - 12/03/12 09:28 AM

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

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Raginar
Post Laureate
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Where to get accurate Longitude and Latitude? new [Re: Doug Culbertson]
      #5551764 - 12/03/12 10:10 AM

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

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csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Where to get accurate Longitude and Latitude? new [Re: Christopher Erickson]
      #5551874 - 12/03/12 11:24 AM

Quote:

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.


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simpleisbetter
Carpal Tunnel
*****

Reged: 04/18/11

Re: Where to get accurate Longitude and Latitude? new [Re: csa/montana]
      #5551885 - 12/03/12 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.


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raf1
scholastic sledgehammer
*****

Reged: 11/18/05

Loc: south Texas
Re: Where to get accurate Longitude and Latitude? new [Re: csa/montana]
      #5551942 - 12/03/12 12:27 PM

Quote:

Quote:

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


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EdmontonAB
Pooh-Bah
*****

Reged: 04/30/08

Loc: Sooke, BC , Canada
Re: Where to get accurate Longitude and Latitude? new [Re: raf1]
      #5552210 - 12/03/12 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.

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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Where to get accurate Longitude and Latitude? new [Re: EdmontonAB]
      #5552541 - 12/03/12 06:24 PM Attachment (19 downloads)

Quote:

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!


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Mary B
Vendor - Echo Astronomy and Electronics
*****

Reged: 05/21/10

Loc: Minnesota
Re: Where to get accurate Longitude and Latitude? new [Re: Christopher Erickson]
      #5552595 - 12/03/12 06:56 PM

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

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raf1
scholastic sledgehammer
*****

Reged: 11/18/05

Loc: south Texas
Re: Where to get accurate Longitude and Latitude? new [Re: EdmontonAB]
      #5552775 - 12/03/12 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

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Starhawk
Space Ranger
*****

Reged: 09/16/08

Loc: Tucson, Arizona
Re: Where to get accurate Longitude and Latitude? new [Re: raf1]
      #5553151 - 12/04/12 12:04 AM

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

-Rich


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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Where to get accurate Longitude and Latitude? new [Re: Starhawk]
      #5553170 - 12/04/12 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.


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Calypte
Pooh-Bah


Reged: 03/20/07

Loc: Anza, California
Re: Where to get accurate Longitude and Latitude? new [Re: Starhawk]
      #5553198 - 12/04/12 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.

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Al8236
Pooh-Bah
*****

Reged: 08/18/10

Loc: 48.9173N 122.1390W
Re: Where to get accurate Longitude and Latitude? new [Re: Calypte]
      #5553355 - 12/04/12 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.


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Raginar
Post Laureate
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Where to get accurate Longitude and Latitude? new [Re: Al8236]
      #5553383 - 12/04/12 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.


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Mary B
Vendor - Echo Astronomy and Electronics
*****

Reged: 05/21/10

Loc: Minnesota
Re: Where to get accurate Longitude and Latitude? new [Re: Raginar]
      #5556341 - 12/05/12 08:12 PM

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

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mich_al
Carpal Tunnel
*****

Reged: 05/10/09

Loc: Rural central lower Michigan ...
Re: Where to get accurate Longitude and Latitude? new [Re: Christopher Erickson]
      #5556402 - 12/05/12 08:53 PM

Quote:

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




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


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Raginar
Post Laureate
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Where to get accurate Longitude and Latitude? new [Re: mich_al]
      #5557029 - 12/06/12 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://earthmeasurement.com/GPS_accuracy.html

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

http://dnr.wi.gov/maps/gis/documents/gps_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!

Edited by Raginar (12/06/12 08:14 AM)


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Bob Griffiths
Getting Grouchy
*****

Reged: 10/10/05

Loc: Frederick Maryland
Re: Where to get accurate Longitude and Latitude? new [Re: Doug Culbertson]
      #5557229 - 12/06/12 10:29 AM

Quote:

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

Bob G.


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Doug Culbertson
Post Laureate
*****

Reged: 01/06/05

Re: Where to get accurate Longitude and Latitude? new [Re: Bob Griffiths]
      #5557449 - 12/06/12 12:29 PM

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

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EddWen
Pooh-Bah


Reged: 04/26/08

Re: Where to get accurate Longitude and Latitude? new [Re: Raginar]
      #5557548 - 12/06/12 01:25 PM

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

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

Quote:



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

Enjoy!




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Per Frejvall
sage


Reged: 09/28/12

Loc: Saltsjöbaden, Sweden
Re: Where to get accurate Longitude and Latitude? new [Re: EddWen]
      #5557648 - 12/06/12 02:30 PM

Folks,

Do not forget that GPS uses an spheroid model of the earth curvature (WGS84) that bears more resemblance to reality in some areas and less in others. Wehere I live (east coast of Sweden outside of Stockholm) the formal GPS altitude - the correct one - is more than 30 meters off the real world altitude.

I know Garmin, in some models, attempt to correct this with rough elevation models, but most GPS receivers will report "correct" WGS84 spheroid altitude as it is (which is most likely wrong in terms of the real world).

If elevation is of importance, I would download elevation data from the internet and see what it says. Google Earth data seems to be derived from an interpolated elevation grid. This most clearly demonstrated by hovering the cursor over a lake surface... At my place, the water surface is lowest in the middle of our lagoon and slightly higher (a few meters) closer to the shore...

I'm ranting here, but point being: the only good elevation data that you can get is either a local survey from your county land office or a dense elevation grid.

Another point worth noting about GPS accuracy is that the figure reported by Garmin's units is an estimate, nothing else. It does not reflect the actual accuracy.

Survey grade equipment is usually accurate down to two millimeters (phase detection) while normal GPS can achieve 0.3 meters. If you want the really cool stuff, you go for a Real Time Kinematic solution with roving units and local reference stations and do post processing. Then you're well below one millimeter

/per


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Raginar
Post Laureate
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Where to get accurate Longitude and Latitude? new [Re: Per Frejvall]
      #5558565 - 12/07/12 12:42 AM

Per,

You can usully change your reference model. For instance, HAE is what we commonly use when we want to be accurate in the military.

He's right about the accuracy of a Garmin; though if you read the article above from the WI DNR, you'll see that it's very accurate. The question is, of course, cost. What are you willing to pay for accuracy? If everyone on your online research team has an iphone, it's probably good enough.

GPS is amazing.


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Per Frejvall
sage


Reged: 09/28/12

Loc: Saltsjöbaden, Sweden
Re: Where to get accurate Longitude and Latitude? new [Re: Raginar]
      #5558588 - 12/07/12 01:13 AM

Yes Chris, you can change it to whatever is available. I am not familiar with HAE (could be because I'm not in the US).

Garmin's assessment of accuracy is surprisingly accurate but some of their receivers (most notably GPS-17 and anything that has the same chip/firmware combination) can take long hikes at times, sometimes up to 150m, before slowly going back to the correct position. I am coastal so I always "diff" my boat systems with IALA corrections via a separate receiver. That in combination with a Hemisphere GPS module that has a really good atmospheric model gets me to a cool and verified +/- 15cm at 95% of the time.

And on topic, my recommendation for most would be to use the iPhone or other smart phone, and if you need high precision altitude, never trust a GPS; contact your county land office and ask the for a gridded or surveyed altitude for your GPS coordinates.

As was correctly stated above, the position is usually less important than the time. Remember that a one second time error in your mount will set you off by 15 arcseconds on the sky!

Oh, I agree; GPS is amazing, especially if you take into account that it is a 70's design!

All the best from a snowy Sweden,

Per


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Raginar
Post Laureate
*****

Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Where to get accurate Longitude and Latitude? new [Re: Per Frejvall]
      #5558781 - 12/07/12 08:01 AM

Here is a like to what Height above Elipsoid means:
http://www.esri.com/news/arcuser/0703/geoid1of3.html

Essentially, it's the native plane of GPS from which it converts to WGS84 or whatever reference system you're using.


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Calypte
Pooh-Bah


Reged: 03/20/07

Loc: Anza, California
Re: Where to get accurate Longitude and Latitude? new [Re: Christopher Erickson]
      #5560164 - 12/07/12 11:34 PM

Quote:

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



You are correct. I did! I was very surprised one time to compare a position from my GPS receiver with the alleged same position in Google Earth. They differed by maybe 100 meters. It was my first confrontation with the concept of "datums." But, oddly, usually the positions are identical.


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Trombone
scholastic sledgehammer
*****

Reged: 07/11/05

Loc: Canadian west (and north!)
Re: Where to get accurate Longitude and Latitude? new [Re: Calypte]
      #5560235 - 12/08/12 12:32 AM

Raginar: Great link. Fascinating read.

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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Where to get accurate Longitude and Latitude? new [Re: Trombone]
      #5560848 - 12/08/12 12:56 PM Attachment (10 downloads)

This is a picture of the custom GPS-based timers I have used a number of times for recent Pluto occultation timings. It triggers the frame grabber on the high quantum-efficiency video camera.

Everyone uses the same timer with the same configuration and the operator manually-logs the GPS coordinates displayed by their timer for later data reduction.

Smartphones with GPS chips will simply not work for this application.

Edited by Chris Erickson (12/08/12 06:43 PM)


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Christopher EricksonModerator
Carpal Tunnel
*****

Reged: 05/08/06

Loc: Waikoloa Village, Hawaii
Re: Where to get accurate Longitude and Latitude? new [Re: Christopher Erickson]
      #5560890 - 12/08/12 01:25 PM Attachment (10 downloads)

Here is a picture of a different, less-expensive type of GPS-based occultation/transit timer. This one has analog video in/out goes in between a low-lux video camera (Mallincam, Stellacam, Orion Starshoot, Watec WAT-120N, etc.) and an analog video recorder. It adds a time stamp overlay to the bottom of each video frame. It can't work with the special, high quantum-efficiency video cameras because they don't have analog video outputs.

Once again, smartphones with GPS chips can't be used for this application.


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SkipW
sage


Reged: 02/03/11

Loc: Oklahoma, USA
Re: Where to get accurate Longitude and Latitude? new [Re: Per Frejvall]
      #5561696 - 12/08/12 11:37 PM

Quote:

Do not forget that GPS uses an spheroid model of the earth curvature (WGS84) that bears more resemblance to reality in some areas and less in others.



Just to clarify one point, WGS84 is an ellipsoidal model, not spherical.

From Wikipedia: "The WGS 84 datum surface is an oblate spheroid (ellipsoid) with major (transverse) radius a = 6378137 m at the equator and flattening f = 1/298.257223563. The polar semi-minor (conjugate) radius b then equals a times (1 - f), or 6356752.3142 m." We use this ellipsoid model daily at work. I haven't checked these numbers for a and b against what we use, from reliable sources, but that .3142 looks familiar.

WGS 84 ellipsoidal height (elevation) does differ in places from Mean Sea Level by up to several dozen meters, so for precision work, especially in elevation, it's important to know what datum you're referencing. If you need centimeter accuracy, from whatever datum, you're probably going to have to hire a surveyor.


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