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Old 13th July 2011, 14:18   #1471
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Default Re: Using a GPS Receiver in the Car

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Originally Posted by NetfreakBombay View Post
That would not happen with decent GPS hardware. GPS is accurate to 5 - 10 meters in PNDs like Garmin / Tomtom. These systems have WAAS support and since November 2010, WAAS is active in India in 300 KM radius around AAI ground stations. this covers most metros like Delhi/Bangalore/Mumbai.

Civilian restrictions start once you try getting accuracy better than 1 meter.
Sir IMHO,
The above discussions was with respect to MMI and Satguides which are Chinese manufectued, Indian labelled.

WAAS in India that is GAGAN is still not fully implemented in India. Isro has conducted PSAT (Preliminary System Acceptance Testing) in Dec 2010. The first GAGAN navigation payload is slated on GSAT-8 which was launched on May 21, 2011. The second GAGAN payload is scheduled to be launched on GSAT-10 2012. The third GAGAN payload is planned in late 2012/early 2014. GAGAN is scheduled to be fully operational by 2013-2014.

Even if one uses Germin with WAAS it will require specific Gagan receiver chip to read the assigned frequencies.

The Civilian codes called C/A codes have an accuracy of 8-15 meters.
Some very high end civilian receivers called dual-frequency receivers which receives part of military code P-code (not the full signal) gives very higher accuracy. However techniques like Differential GPS (D-GPS) can give accuracy of less then 3m.

However the best of receiver will not assure the advertised accuracy 100% of time. Because accurecy of signal depends on various other conditions, parameters and components such as:
*Ionosphere and troposphere delays
* Signal multipath
* Receiver clock errors
* Orbital errors
* Number of satellites visible
* Satellite geometry/shading
* Intentional degradation of the satellite signal
Detailed here: How Accurate is your GPS ?

At times and it has happened to me that My MMI navigator has shown my positioned to be on adjacent/close by road.
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Old 13th July 2011, 15:34   #1472
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Default Re: Using a GPS Receiver in the Car

^^^^
For example following is my GPS trek from last month trip to Spiti.
Using a GPS Receiver in the Car-gps-trk.jpg
White line is my GPS log.
Yellow line is road trace from the image file.
Actual road lies between the above two lines.
The distance between the actual road and GPS trace(White Line) is about 19 meters (measured in Google map-Small line between two red dots).
The distance between the Map shown road (yellow line) and the GPS trace is about 29 meters.

This above map clearly demonstrates both kind of error (Map error & Signal error) I had posted in my previous posts.
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Old 13th July 2011, 19:07   #1473
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Default Re: Using a GPS Receiver in the Car

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Originally Posted by dinesha View Post
The above discussions was with respect to MMI and Satguides which are Chinese manufectued, Indian labelled.
Both provide maps in Garmin format, and with Garmin unit I regularly get 5 meters accuracy. I am using Satguide maps on Garmin unit.

When I use the same maps on my phone (Nokia 5230) I do get error such as:

1. Phone detecting Car on flyover while I am on service road
2. Car getting detected on a parallel road


Overall, what I am trying to say is; quality of hardware device matters in addition to quality of maps.

Regarding WAAS, as I mentioned it is not fully operational. But it works in Metros. reason is AAI needs this to work for ILS to be operational and is main sponsor of WAAS in India. You can turn on monitor mode in GPS and check signals in Kozhikode, Hyderabad, Nagpur (apart from Metros).

Frequencies in India are L1 and L5. Units purchased in US would just work out of box.
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Old 13th July 2011, 20:50   #1474
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Default Re: Using a GPS Receiver in the Car

Hi,
I thought we lost the first GAGAN payload in the GSLV crash.

The accuracy shown on GPSrs is a probability estimate. Some NMEA sentences output the DoP values. If you have a SiRF3 based system which stores native (.sbn) you can get a lot of information for postprocessing. But you get what you pay for. Check out Trimble.

Best way to get an accurate track is to average multiple GPS tracks. Even then, if you have HiRes orthorectified images, these are preferable to GPS tracks.

In cities, one has multipath reflections, severely affecting accuracies. Navigation software usually implement a 'lock on road' feature. Which in case of bad signals can make you jump streets.

Roads are best characterised by a speed index. Without this, the algorithms really can't distinguish amongst the various roads.

Hope this sufficiently confuses.
Regards
Sutripta
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Old 14th July 2011, 19:43   #1475
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Default Re: Using a GPS Receiver in the Car

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Originally Posted by Sutripta View Post
Hi,
I thought we lost the first GAGAN payload in the GSLV crash.

The accuracy shown on GPSrs is a probability estimate. Some NMEA sentences output the DoP values. If you have a SiRF3 based system which stores native (.sbn) you can get a lot of information for postprocessing. But you get what you pay for. Check out Trimble.
We lost the first payload slated on GSAT-4 in April 2010.
I think even Germin uses SiRFstar III chips in some of their handheld products.
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Old 14th July 2011, 20:43   #1476
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Default Re: Using a GPS Receiver in the Car

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Originally Posted by dinesha View Post
We lost the first payload slated on GSAT-4 in April 2010.
I think even Germin uses SiRFstar III chips in some of their handheld products.
Garmin used to use SiRF3 in the 60cx and 76cx range. But did not use the drivers given by SiRF. No .sbn or .sbp files in those.

Amongst smartphones, I think HTC, and now Samsung Galaxy2 use SiRF. But dont know their native storage format.

The advantage of the .sbn files was that it was documented by SiRF.

Regards
Sutripta
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Old 14th July 2011, 20:53   #1477
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Default Re: Using a GPS Receiver in the Car

Quote:
Originally Posted by NetfreakBombay View Post

Regarding WAAS, as I mentioned it is not fully operational. But it works in Metros. reason is AAI needs this to work for ILS to be operational and is main sponsor of WAAS in India. You can turn on monitor mode in GPS and check signals in Kozhikode, Hyderabad, Nagpur (apart from Metros).

Frequencies in India are L1 and L5. Units purchased in US would just work out of box.
WAAS is not related to ILS. ILS is purely a ground based system and got nothing to do with GPS. GAGAN is the Indian equivalent of WAAS (US). GAGAN is mainly 'sponsored' by AAI which, once operational, would be utilized for GPS based landing of suitably equipped aircrafts in airports. GAGAN (L1 frequency) is compatible with WAAS and existing GPS/WAAS receivers can receive and process GAGAN signals if initialized properly. GAGAN test transmissions were going on in 2009. A new satellite was recently launched which has a second GAGAN payload.

For the normal user, GAGAN would help to improve the position accuracy. Although under normal visibility conditions plain GPS would give positional accuracy within a few meters.

There is another navigation system being developed by ISRO: - IRNSS (L5 frequency). This is a GPS replacement, and its a long way to go. This requires a new receiver.

Going by the pace of current technological advancements, a multi system/multi frequency GPS receiver is not far, where it can receive any system and give superior position accuracy within a few cms.
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Old 12th September 2011, 14:03   #1478
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Default

hi new to this forum,

Almost all handheld gps/ automotive gps comes with a glass mount cradle and a cigarette light power adapter.

Garmin GPSMAP 60 CSx, Zumo etc

Quote:
Originally Posted by NetfreakBombay View Post
Both provide maps in Garmin format, and with Garmin unit I regularly get 5 meters accuracy. I am using Satguide maps on Garmin unit.
=========
Frequencies in India are L1 and L5. Units purchased in US would just work out of box.

Hi,

Can I clarify the following?

IS GAGAN operational as of now? Coz, if I enable WAAS, I do get d just above my satellite page, which stands for differntial signals. But I must confess I use to get the D even before GSAT8 was launched.

I live in Kozhikode. The cities u mentioned are where ground based reference stations are established. Any info on the current status of GAGAN will be appreciated. The last update from ISRO around June was the navigational payload of GAGAN is being tested from Kundanahalli near to Bangalore.
Cheers

Last edited by Technocrat : 12th September 2011 at 21:05.
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Old 15th November 2012, 14:51   #1479
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Default Re: Using a GPS Receiver in the Car

Hi guys,

Have a Nokia E6 and looking for downloading the google maps(or any good maps) for my trip to MM Hills. I'm a total noobie in this matter. Please guide me on how to download,install and make my E6 to view maps offline.

Thanks,
Ramki
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