Different map datum?

[Summit600]

Hi,

I have a Magellan 500LE and it works very good whenever i manually mark a position out in the field and press GOTO in order to go back to it. But when i try and create POI's from my computer, its not accurate. I was looking in Google earth near my house and found a trail that turned off the road so i entered the coordinates into my GPS from the notepad editor. And when i actually went out for a walk to find this trail it was off by 17 meters... im not sure what is going on here?

sorry if that doesn't make sense thats the best way i could describe it.

Thanks

[+trainlove]

I'm not sure about the Magellan 500LE, but my Magellan Gold's street maps (MapSend Topo) are based on the US Tiger Census database, which is almost 10 years old. Lots of spots do not seem to be correct, don't stand in the middle of an intersection but you will see that it's up to 100 or more feet off.

 

I don't think this has anything to do with the Datum, but I would be curious to know what the Datum that the US Census used in 1999 when creating the free street database. That information does not seem to be anywhere.

[+trainlove]

Will the forum moderator please remove all but one of these replies.

And in the future please prevent it from happening again and again as seen in almost any post.

[Hertzog]

Hi,

I have a Magellan 500LE and it works very good whenever i manually mark a position out in the field and press GOTO in order to go back to it. But when i try and create POI's from my computer, its not accurate. I was looking in Google earth near my house and found a trail that turned off the road so i entered the coordinates into my GPS from the notepad editor. And when i actually went out for a walk to find this trail it was off by 17 meters... im not sure what is going on here?

sorry if that doesn't make sense thats the best way i could describe it.

Thanks

Google Earth is generally more accurate than that, but I've seen instances where it was clearly off by that much. You should check your datum (make sure it is set to WGS 94), but most likely it's just the Google Earth registration at that particular area.

[AlunS]

Google Earth is generally more accurate than that, but I've seen instances where it was clearly off by that much. You should check your datum (make sure it is set to WGS 94), but most likely it's just the Google Earth registration at that particular area.

The registration between reality and the satellite / aerial imagery is very bad in places, so 17m is doing pretty well, I'd say.

[+Cardinal Red]

Will the forum moderator please remove all but one of these replies.

And in the future please prevent it from happening again and again as seen in almost any post.

 

I have just a few more forum posts than you, and have never had a double post. NEVER. Yes, the system is slow to respond sometimes. But, I am sure YOU are part of the equation here. You are obviously continuing to click when you don't get instant confirmation of your post. I suppose TPTB could institute some form of posting flood control, but you could chill and show a little more restraint also. Now I await your response indicating this was the result of only one click, and you are obviously not responsible. Just don't expect me to believe it.

[+trainlove]

No, it's likely that I pressed the submit button at least 32 times over the course of about 4 minutes. I had gotten fed up and walked away before that last press and it was still just hanging. Until immediately upon pressing it that very last time, conpiracy here?

 

If TPTB are aware of such a state of affairs they should implement a fire control system. Or even put a disclaimer at the bottom of a post screen stating, IF YOUR BROWSER DOES NOT IMMEDIATELY RESPOND TO YOUR SUBMISSION. PLEASE WAIT AND DO NOT PRESS THAT BUTTON AGAIN>

 

Edited to add:

Back to the point of this posting. With MapTech Terrain Navigator topographic maps on my computer at their highest zoom level on 1:24K topos, I think 1 pixel is 12 meters.

Not sure how that compares to Google Earth or maps.google.com.

 

Also be aware that unless you have a Military grade GPS you will have something like 1 sigma of 10 meters, but that depends on your DOP or EPE.

Edited January 2, 2008 by trainlove

[+tabulator32]

No, it's likely that I pressed the submit button at least 32 times over the course of about 4 minutes. I had gotten fed up and walked away before that last press and it was still just hanging. Until immediately upon pressing it that very last time, conpiracy here?

 

If TPTB are aware of such a state of affairs they should implement a fire control system. Or even put a disclaimer at the bottom of a post screen stating, IF YOUR BROWSER DOES NOT IMMEDIATELY RESPOND TO YOUR SUBMISSION. PLEASE WAIT AND DO NOT PRESS THAT BUTTON AGAIN>

 

Edited to add:

Back to the point of this posting. With MapTech Terrain Navigator topographic maps on my computer at their highest zoom level on 1:24K topos, I think 1 pixel is 12 meters.

Not sure how that compares to Google Earth or maps.google.com.

 

Also be aware that unless you have a Military grade GPS you will have something like 1 sigma of 10 meters, but that depends on your DOP or EPE.

 

Sometimes it helps if you lay the GPSr on the ground for a couple minutes and let it "catch up" on its computation (in order to get a more accurate mark) prior to pressing "Mark".

 

And, for the server hiccups, I find those occasional 45-second delays a perfect time to grab another cup of tea or something. If you're going to grab something to drink, make sure its decaf, mmmmmkay?

 

[+trainlove]

Because the moderator deleted the requested messages one can't see that in this instance it wasn't a 45 second server burp, it was 6 minutes from 08:13 AM to just about 08:19 AM.

Too bad the Post #'s get adjusted automatically also.

But it is a good thing that only one instance of my multiple posting shows up in My Last 10 Posts in My Assistant, or in a Search of posts by me.