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  1. #261
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    Hi,

    This topic has been forgotten?

    What a pity!

    []'s

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  3. #262
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    This topic is not forgotten, we still search for solution

  4. #263
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    @rfb
    Remember my previous analogy. Loly is the arch-typical 'Swan on the Pond'. Sometimes not much apparent on the surface, but plenty of action below.

    k1638031
    The answer to this problem requires a lot of skill and patience, Loly has both in abundance. I have only one (guess which ....?).
    'Thanking Posts' are banned. To thank someone, and/or to see hidden links and content, use the [Only registered and activated users can see links. ] button below left of the helpful post then refresh your browser [F5 key]. 'Thanking Posts' are banned.
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    [Only registered and activated users can see links. ] should make their first post as a new Intro Thread in [Only registered and activated users can see links. ].

  5. #264
    Navigation software expert Kanopus's Avatar
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    Is it really a problem? I mean, could you define the problem without a reference to satellite screen? And get any evidence?

    As for accuracy on satellite screen, using photoshop is an example of a working solution
    Thanks, Kanopus

  6. #265
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    Quote Originally Posted by Kanopus View Post
    Is it really a problem? I mean, could you define the problem without a reference to satellite screen? And get any evidence?

    As for accuracy on satellite screen, using photoshop is an example of a working solution
    I have had similar doubts, but googled and understood clearly that, yes, we have a problem. The values shown are not mere rates obtained directly from satellites that are shown on the screen, they are the result of complex calculations made ​​in gps. If we have the same hardware with distinct aparent accuracy on different firmwares and these values ​​represent coordinates position and other derivatives, all differents and fruits of calculations, then we have a problem.

    I believe that nobody of good sense here has the illusion that these values ​​are absolute, true, far from it (but we have faith, lol). Our GPS navigation receive only raw data untreated of L1 frequency, and algorithms, database and processing capabilities of the device are unable to perfectly correct distortions of ionosphere, troposphere, orbit errors, timing, signal reflection between others. These distortions, experts say, can lead to errors of up to 10 meters, but we are not discussing the real accuracy that we could only achieve with our garmin if it could capture raw data from the satellites for later to be post-processed on servers with powerful software.
    How much of distortion has the precision on the screen in relation to real coordinated, is another discussion, by the way, the path that we are following in forum of my country. But the issue here is another: we are in the battle for to try to get that the modified 3790 presents the same "accuracy" of the 3790 original, even if the 3 meter of the screen represent 50 meters in reality. If both gps work equally means they are doing their calculations properly as they were designed, and that has nothing to do with aesthetics, appearance or "photoshop", my friend ..

    Finally, yes, you can set without reference screen satellite: just, for example, record waypoints or tracklogs of 2 or more gps, side by side, and check the discrepancies and relative accuracy among them. If the 3790 exit outside the standard certainly will prove to, once again, that the problem of relative precision is real (off road mode, look on road off ..)
    Last edited by angelozip; 4th March 2013 at 07:28.
    Nuvi 2689; 3490; Etrex 30; Oregon 200 (from Approach S5)

  7. #266
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    Quote Originally Posted by lolypop000 View Post
    This topic is not forgotten, we still search for solution
    Me too, but I am part of the manual workers,
    Well, I keep checking the apparent accuracy of my 3790, became routine and fun, lol .. The difference is that now I always have other gps to compare, could be an 3790 original, but is a Etrex 30 or Oregon 450, also good references. For example, right now I just do static measurements for about 15 minutes and accuracy values ​​between 3790 and Oregon 450 were equal, yes! (less the height, disparate). Comparisons with the Etrex 30 made ​​at other times were more rigorous and in moving. In these situations the Etrex 30 almost always fared better, especially in motion, but the 3790 values were not as bad as the comparison I made weeks ago with another 3790 original (see video in previous post). Everything indicates that the effect of the real Cold Start + delete GPS folder was effective, although it has not yet matched, apparently, the accuracy of the 3790 original (lack do these tests with it). To better clarify recorded several tracks of both and at the same time, I believe that good indication discrepanciais between both. Opportunely, as soon as properly analyzed, will present the results.

    Everyone knows, I believe, that the values present in gps are results of calculations of complex algorithms to determine the position with some degree of accuracy, from the raw data received of the satellites. Corrections satellites data vain from ionospheric distortions, orbits, reflexes, timing .. and also distortion of the oscillator, according to the different working temperatures of the device (internal and environmental). In other words, if we have the same hardware (3790) and the precision values ​​presented are quite different between two different firmwares, it is more logical to assume that the basis of calculation (tables, constants) or the algorithm of firmware of them are different. At the start of the topic has been discussed this issue from an important text of Engineering of Garmin (indicated by Catymag) which dealt specifically of a dynamic table with correction factors for the oscillator (which enables synchronization with the frequency of the satellites) in according to different internal temperatures of the gps. This table with the correction factor or factors, would be pre-installed at the factory. Question: would also be installed with the firmware of 3490 when flashing the 3790? Or it would be different calculation algorithms in both firmwares? Answer not very easy, but the most important is to know where and how to identify such region table, factor (constant) or algorithm and who knows thus be able to make some any "transplant".

    Really looks like a great challenge, but I believe that I have a clue that may indicate at least the region: the mt.nvm file that is in the folder .System/GPS. The first hint is the proper termination of the file .nvm, it seems Non Vol Memory, but that's just supposition. Significant is that it is perceived that this file is created before of tunning of satellites, because its creation time is always 1 or 2 minutes shorter than the Arc.bin and Bee.bin files, that seem to be created at the time wherein the satellites are tuned. In other words, the mt.nvm is created from reading some region of the Non Vol Memory, and everything indicates that the region is not 41. So how to find out of which region he comes? Examining content's file so that the GPS is turned on, and seeking similar patterns in firmware gps, a way of knowing that the memory region they come. The data in this file, stored in non vol memory, plus current data of ARC.bin and BEE.bin files, should be the basis for the calculation of precision made ​​by the algorithm of positioning (accuracy), probably.
    Last edited by angelozip; 4th March 2013 at 07:19.
    Nuvi 2689; 3490; Etrex 30; Oregon 200 (from Approach S5)

  8. #267
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    During weekend I have tried some even more hard approach to the matter. I’m not fluent in software changes, so that was my way to try to do something.
    I simply erased all the files, formatted the nuvi and load all the content back.
    Might be it was my mistake that I have started from 3790 SW and after format and copying the files from 3490, because after copying the files the updater refused to update with 3490 7.10SW, but asked for some 3790 SW. I’ll be glad someone more experienced to share his background why that happened.
    Anyway – no improvement in accuracy.
    Tomorrow I’ll test it on long distance road in different city conditions and will report.

  9. #268
    Navigation software expert Kanopus's Avatar
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    Quote Originally Posted by angelozip View Post
    Finally, yes, you can set without reference screen satellite: just, for example, record waypoints or tracklogs of 2 or more gps, side by side, and check the discrepancies and relative accuracy among them.
    Yes, this is exactly my idea. And logic says, that until someone provide this data, we should assume that problem doesn't exist or at least is not well defined.

    Actually we have talked about problem as a result of conversion form 37xx to 34xx. In my opinion this is not real. Nuvi 37xx has weak GPS receiver. Problems with slow fix and tracking errors could be observed regardless of conversion. This was already described in reviews over two years ago, before 34xx was released:
    Code:
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    Thanks, Kanopus

  10. #269
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    Thanks Kanopus for the links.
    Vs:Mobile XT/ 3790 Vs5.0 HWID1101-Firm2.60/ 3597 Vs5.4 HWID1603-Firm4.60
    Mapa: CNSA 2017.20,AutoGuia 4.20,TRC 16.10, OSM SA 16.11, 3DMap,G2S,ASR,JCV,SID,BaseMap,DEM,Traffic.
    POIs: GPS INFO + Travel Guide + Vozes + Veiculos

  11. #270
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    Quote Originally Posted by isg View Post
    Tomorrow I’ll test it on long distance road in different city conditions and will report.
    The effect was .
    The same old bad accuracy. It seems to me that the accuracy does not depend on environmental conditions only. Even not moving there are some significant drop downs in satellite bars resulting in bad accuracy. For yesterday trip average accuracy was more than 25-30 m. which means bad bad bad positioning.
    More or less I should agree with Kanopus that there should be and hardware reason for the bad accuracy. It is true that even with original 3790 SW in the very beggining of the model there are accuracy problems. But at that time 3790 was best of the best, so at that time it seems to me normal….
    Because of yesterday experiments I have decided to buy 3597 immediately when available and to close the case.
    Till that moment, I’m opened for any tests suggestions with the unit, as I’m not “in love” in it any more.
    Last edited by isg; 6th March 2013 at 09:51.

 

 
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