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Posts posted by brian.r.hamilton

  1. BTW, I do have all of the US topo maps on an 8 GB card, but using 2 img files (with only one loaded at a time - east & west US). Each img file is still subject to the 4 GB file size limit. There is no way around that as far as I know.


    Also, the topo maps I use are at http://gpsfiledepot.com/maps/byuser/49. The trail data is at http://gpsfiledepot.com/maps/view/53. There are lots of other maps, trails, GIS data, etc. at GPSFileDepot.com.

  2. I haven't taken the time to catch up on this thread but was notified of a recent reply. Seemed like a perfect opportunity to mention GPSFileDepot.com. You can download all kinds of great topo maps there for free & they are much better quality than Garmin IME - at least better than TOPO 2008 that I have. There is also a great transparent layer called MyTrails with tons of trails from all over the country. If you send the author GPX files of your local trails, he will add them & include them in the next version!


    Also, I'm currently using an 8 GB micro SD card with the entire US & the trails layer on it with zero problems on my good old reliable & very accurate HCx.

  3. The chipset update has really changed the behavior on my GPSr. The satellite enumeration problem has been fixed. I'm getting considerably different data when stationary. The "movement" with the previous version was "blocky" but now it is just wandering... much more like my old Vista C behaved. I'm not sure if this is an improvement or not yet. I need to gather more data. The data points I collected so far seem to wander further away from my actual position than the previous version, but not by much. The data looks more "realistic" now. It was obvious something was wrong with WAAS enabled before.


    PS. I had to run WebUpdater 3 times & power my GPSr on/off quite a bit before the 2.40 update was properly applied. Fortunately it made it despite the GPSr crashing. The chipset firmware update went smoothly.

  4. If you are in a heavily wooded area with lots of trails, with lots of trail intersections, more points can be the difference between getting somewhere on time vs. being really late. If that hasn't happened to you, you either haven't done as much exploring as you claim or you're a liar.


    It's sort of like having one of those silly MP3 players that has 2 G of memory but can only store 5 minutes per song yet you would like to listen to an hour long audiobook. The device is perfectly capable but the software prevents you from making full use of the hardware. Another example is how some digital cameras limit video clips to a few minutes instead of allowing recording up to the limit of memory on the device. I'm no pro at making analogies, but it doesn't take an "expert" to understand the shortcomings of Garmin's choices here. I don't see why an expert such as yourself would even need a GPS!


    The point is that some of these devices have lots of memory & many of us would like to see it used more effectively. Nobody really cares if that has any value to you. You've already expressed your opinion there. Garmin made their design choices when memory was more precious than it is now. Modern devices have enough memory to allow for MUCH more flexibility that many of us would appreciate.

  5. I've seen satellite 13 displayed on the right & twice too but I didn't check to see if it was really satellite 51. It did indicate it was broadcasting corrections (displayed "D"). I didn't check to see if there were multiple satellite icons numbered 13 or 49. I'll try to remember to watch for some of these details, but I agree that it's looking mostly like a display bug right now.


    However, today I noticed that with WAAS off on my HCx, my average position was quite a bit more inaccurate than my Vista C with WAAS off. I gathered track points every second for one hour, at the same time with each unit from the same stationary location outdoors. The Vista C error increased with WAAS off, but the average position was almost exactly the same as the average position with WAAS enabled. On my HCx, the average position with WAAS enabled is the same as my Vista C, but with a much tighter grouping of track points. With WAAS off, the HCx average position moved more than 20 feet for some reason. By the way, the data I took today also showed the HCx with WAAS off generating a grouping of track points as tight or better than the Vista C with WAAS on. Too bad the average location was a little off. I would need to do more reading & testing to be sure, but this could indicate a rounding error in some math in the firmware.

  6. I just looked at some data I collected yesterday & WAAS enabled seemed much better! I'm running some more tests today to confirm. If what I find today confirms what I saw yesterday, my Vista HCx is outperforming the Vista C by quite a bit with WAAS enabled!


    Maybe the recent satellite changes were actually causing problems with WAAS & the satellite numbering issue is simply a display error.

  7. It looks as though my HCx is displaying 49 for 48 (PRN 135).


    Perhaps it never even tries to lock 51 because "48" is so strong (full bar on display). Maybe my Vista C goes after both 48 & 51 bedcause they are usually less than 2/3 strength.


    I called Garmin last week & the technician said he would report the issue & get back to me Monday (2 days ago). Haven't heard anything yet.

  8. The GPSr displayed accuracy is just one estimate based on the algorithm used in your GPSr. Comparing one unit's measure to another is probably pointless unless you know exactly how it is calculated. Even then, the displayed accuracy still may not be very useful to you.


    A more useful (in my opinion) measure of the accuracy can be obtained by simply plotting tracks over calibrated maps. Don't forget to configure your GPSr to gather track points however you feel is most useful to you. If your GPSr is not moving, the points should be very tightly packed together with no spurious points away from your location. Aerial photo maps with known benchmarks are also handy for checking real world accuracy.


    I think the best accuracy any of my GPSrs has displayed was +/-7 or 8 feet. I have no idea if Garmin displays the 95% accuracy or something else. Both my Vista C & Vista HCx will display the same accuracy, but the HCx collects track points that are quite a bit more accurate when not moving. When moving they are very similar except that the HCx does better in difficult terrain (as advertised). Both have been worse with WAAS enabled lately.

  9. Both my Garmin GPSrs let me know when I need to calibrate the compass. There is a "need to calibrate" message that pops up. This will usually happen if you are a fair distance from where you last calibrated your GPSr. I'm not sure what the exact number is or exactly how Garmin determines calibration is necessary, but it happens a few times each year for me when I travel about 50 miles or so from my usual location.

  10. Is the DEM data saved in a grid format, essentially one independent "layer" in the Garmin IMG file or does each zoom "layer" have it's own DEM data?


    Also, where can I find good documentation on the IMG file structure? I've browsed a document on SourceForge named imgformat-1.0.pdf, but it makes no mention of DEM or elevation data & seems rather incomplete.

  11. I thought waypoints use the current GPS elevation? Are you talking about setting a waypoint (via the GPSr) somewhere other than your current position? If so, I didn't even realize that was possible!


    I don't find DEM data on the GPSr itself useful at all - essentially zero value to me & I suspect many others unless there is just something really cool to do with it that I've never thought of.


    PS. I actually just created a waypoint on the GPSr somewhere other than my current location & it does not include any elevation data on the Vista HCx at least. Now that I think about it, this could be a useful feature for many reasons though... maybe even more useful than having all the US in my GPSr.

  12. I didn't realize (or believe) Garmin MapSource actually sent DEM data to the GPSr! I knew it displayed elevation at the cursor position, but I never use that for anything so I never really gave it any thought. Not being familiar with the *.img file structure, the first thing that came to mind was that they would interpolate a point between the contour intervals. Wasting space for full DEM data seems sort of dumb or at the very least something that should be optional.


    Now that I've read just a little about the *.img files & map creation process, I see there sure is a need for better tools to best make use of all this map data. It's too bad Garmin doesn't provide these options. Is cgsMapper optimized yet because the amount of processing time these things take seems absurd. I write software for embedded systems (DSPs), not PCs, so maybe I just have a different perspective or am simply underestimating the work involved.


    PS. Does the elimination of the DEM data at the GPSr speed the screen draw time at all?

  13. Is my Vista C considered that old already? :o


    My HCx continued to display the "D"s for at least 10 minutes despite not having any WAAS satellite signals. It didn't give up until I disabled WAAS. I guess all this clearly indicates a bug. I wish I would have looked at it more closely before installing the new 2.3 firmware.


    Does anyone else see the same behavior with their HCx? If so, what version firmware are you using?


    PS. The HCx appears to use a chipset by MediaTek.

  14. When I first power-up my Garmin eTrex Vista HCx, it displays satellite 49 (PRN 136 I assume) when WAAS is enabled. After a minute or so, it shows a full strength signal with solid coloring for 49 & "D"s for all the other non-WAAS satellites, but never a "D" for 49 itself. It never picks up any other WAAS satellites & won't use the last channel of the receiver.


    If I bring the GPSr indoors, 49 is lost & 13 takes it's place. 13 remains hollow but the "D"s are still displayed on all other available satellites for longer than 2 minutes (as long as I was in the house - probably at least 10 minutes). If I carry it back outside, 13 won't go away but shows full strength although it remains hollow & the 12th channel remains unused.


    Next, if I disable WAAS, the "D"s disappear but the GPSr still refuses to use the additional 2 channels. Enabling WAAS causes 49 to pop back up just as in the beginning.


    Whenever WAAS is enabled, I see spurious track points compared to the nice tight grouping I get with WAAS disabled.


    I was able to select "New Location" once, despite it being grayed out, but it still did the same thing. Now "New Location is grayed out & I cannot select it. I have not tried a hard reset yet.


    For comparison, my Vista C always gets satellites 48 & 51 at about 60% strength (48 hollow, 51 solid) for WAAS corrections & 51 (along with all other non-WAAS satellites) display "D".


    I can't find much information on PRN 136 other than 1 reference to Inmarsat. This sure is starting to look like some sort of firmware bug for the HCx. I have the latest version with the "WAAS fix". I'll try a hard reset next.


    Any idea what is going on here?


    PS. I'm on the U.S. west coast.

  15. I've noticed that my eTrex Vista HCx has better actual accuracy with WAAS disabled.


    When stationary, WAAS disabled yields a tighter grouping of track points with zero spurious points. With WAAS enabled, I get quite a few spurious points away from my actual position. Whether I'm stationary or moving, the displayed accuracy is essentially the same (~+/- 10 feet), but the real accuracy (judged by satellite images) is better with WAAS disabled.


    Anybody else notice the same thing?


    PS. I have the latest firmware (version 2.30) & have been careful to check the WAAS setting while gathering data.


    PPS. I'm on the west coast of North America.

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