DGPS, EGNOS, 3D fix?

[what_the_duce]

Hi, I'm a newbie with GPS and having read a bit I have a few questions.

Do all modern receivers provide a 3D fix, i.e., long, lat, and altitude? I've tried TomTom and it doesnt report altitude in its GPS status window. Does it mean it ignores the altitude? Or is it my Qstarz 818 unit not calculating altitude?

The globalsat 359 specs report horizontal accuracy of 10m and 1-5m with WAAS correction. I imagine its the same with EGNOS correction but I read somewhere that 1 EGNOS satellite actually makes it worse. How do i know which is EGNOS satellite in tomtom or other software? is it 33 and 44? And which one is the bad one? Does DGPS and WAAS/EGNOS one of the same thing?

I've seen people discuss NMEA stream from their receiver? If I get globalsat 359, how do i read its NMEA stream and make changes to 359's settings?

quite a few questions there. please help.

[mikealder]

Welcome to the forum, TomTom isn't interested in altitude so it doesn't display it or use the information provided by the receiver.

Your GPS device will transmit the altitude data, but this data is not relative to sea level, it is a rough approximation of a round ball (the planet Earth is not a round sphere) - this can lead to strange values for altitude.

Other applications can and will display the height information - have a look at tchart for an application that will show altitude, it is available in demo format to try first, if you want to look at the NMEA data stream from your unit you can do this with a terminal server application on the PDA or PC, but you need to parse the data to make it inteligable to be honest - Mike

[what_the_duce]

Thanks for the reply. So there aren't any PC applications that will read the data off my bluetooth connection and display it in terms of the NMEA commands? I've heard people tweak their bluetooth receivers. How do they achieve that. I guess SiRF receivers can be tweaked using SiRFdemo, but what about other chipset receivers?

btw, if tomtom ignores altitude, how does it know if I'm going over or under a flyover? Even if absolute altitude value may be incorrect, i reckon one could make use of relative altitude value (relative to previous altitude readings).

[what_the_duce]

tchart looks really good. shame, it doesnt seem to support UIQ3 (afaik).

[mikealder]

What hardware are you trying to display the data on, it might be easier to point you in a general direction than second guessing, OK so its an NMEA compliant GPS receiver, what device(s) are you trying to use it with? - Mike

[what_the_duce]

i bought qstarz 818 receiver (MTK chipset) to work with SonyEricsson P990. But I'm returning it as it has problems with bluetooth dropouts.

I'm thinking about going for Globalsat 359. To be honest, right now, i'm just trying to learn about the whole GPS scenario... the technology (SBAS etc.), chipsets, protocols, how to tweak units, different maps (off-road moving maps etc.).

So, just looking to having a general discussion about the various things that I got confused about. For example, i just figured out that 2D fix and 3D fix is all about the number of satellites acquired (3 or 4 variable equations to solve). And i "was" thinking it had something to do with chipsets!!

If i do go for 359 unit, I'd want to be able to tweak it using a PC.

[RQ]

Hi,

Have a look at this site for various software applications that can be added to your TT. And, some do have altitude - relatively speaking.

http://www.webazar.org/tomtom/plugins.php?lang=uk

Regards

[what_the_duce]

continuing my noob questions... how do i get GPSinfo to work? I have got globalsat 359. While it works well with my smartphone, i cant get GPSinfo to connect to it using bluetooth serial port.

i'm running winxp with widcomm BT stack. BT serial com port is set to 15 in widcomm settings.

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