| Versions |
  |
|
| Author |
 Topic  |
|
|
Virgilio
Brazil
2 Posts |
 Posted - 04 janv. 2012 : 18:59:48
|
Hi guys,
I'm doing a research about GPS using a ND-100S USB Dongle GPS Receiver. The problem is that it just provides me a NMEA file with my position and what I'd like to access is the info he used to calculate my position. By using SirfDemo, I was able to download the almanac and the ephemiris from my GPS chipset but I haven't found any information about the meaning of which number it provides me.
Below it's the data I get from SirfDemo. I wish to process this info to calculate myself my position using a different algorithm.
Thanks.
/
// Ephemeris Collection Time(UTC): Mon Oct 24 00:28:36 2011
//
//
//
2, 28, 44676, 40640, 0, 0, 0, 0, 0, 0, 56067, 5850, 0, 3887, 31272, 2, 28, 44680, 769, 26165, 24350, 46713, 15361, 25605, 26621, 58138, 50849, 3262, 47638, 55808, 2, 28, 44684, 112, 27548, 19630, 112, 9795, 58430, 3998, 35060, 48001, 65446, 28931, 65452
4, 28, 44676, 40640, 0, 0, 0, 0, 0, 0, 62035, 5850, 0, 25635, 21792, 4, 28, 44680, 21250, 48947, 37792, 54669, 1, 43525, 5488, 27420, 31649, 3557, 60950, 55808, 4, 28, 44684, 65479, 27727, 22867, 65479, 9786, 25478, 3252, 8185, 5028, 65448, 27219, 2128
9, 28, 44676, 40640, 0, 0, 0, 0, 0, 0, 62528, 5850, 0, 5646, 59408, 9, 28, 44680, 16638, 58920, 39109, 38193, 6911, 15624, 51842, 51482, 26017, 3407, 4630, 55808, 9, 28, 44684, 229, 60329, 49099, 229, 10266, 58467, 4825, 16702, 13796, 65451, 44352, 64696
12, 28, 44676, 40657, 0, 0, 0, 0, 0, 0, 58956, 5850, 0, 5123, 64244, 12, 28, 44680, 19461, 49968, 3545, 51435, 20229, 10241, 54256, 26636, 20641, 3352, 25110, 55808, 12, 28, 44684, 65500, 6081, 905, 65500, 10191, 9835, 8876, 64838, 9635, 65446, 38988, 4212
15, 28, 44676, 40640, 0, 0, 0, 0, 0, 0, 59925, 5850, 0, 3058, 45028, 15, 28, 44680, 5621, 48441, 22586, 22739, 61687, 32001, 62521, 15882, 6561, 3486, 12822, 55808, 15, 28, 44684, 65525, 49361, 29774, 65525, 9885, 63312, 8878, 64771, 1627, 65441, 21525, 59924
17, 28, 44676, 40640, 0, 0, 0, 0, 0, 0, 59683, 5850, 255, 61462, 11728, 17, 28, 44680, 9206, 1587, 7765, 17595, 59127, 32259, 27519, 36110, 33185, 3256, 31254, 55808, 17, 28, 44684, 65475, 17138, 6291, 65475, 10028, 21922, 7839, 40473, 59421, 65445, 12323, 60640
28, 28, 44676, 40640, 0, 0, 0, 0, 0, 0, 59975, 5400, 0, 7178, 15384, 28, 28, 44680, 18182, 7984, 54596, 31809, 62980, 47624, 57310, 19980, 7841, 3479, 59413, 6144, 28, 28, 44684, 65328, 6342, 15927, 65328, 10183, 8680, 8833, 45958, 33830, 65446, 10823, 5120
----------------
|
|
|
Ads
|
|
|
gpspassion
93402 Posts |
|
|
micmail
Italy
26 Posts |
Posted - 05 janv. 2012 : 00:05:23
|
Hi,
Maybe there is no need to contact SiRF (good luck!).
The data you see is the decoded version of the ephemerides as SiRFdemo has dumped them on the file.
For example, take a look at the "SiRF Binary Protocol Reference Manual", revision 2.4, November 2008, at page 3-23 where MID15 is specified.
It is quite clear what those numbers mean:
quote:
The data area consists of a 3x15 array of unsigned integers, 16 bits long. The first word of each row in the array ([0][0], [1][0], and [2][0]) contain the SV ID. The remaining words in the row contain the data from the navigation message subframe, with row [0] containing sub-frame 1, row [1] containing sub-frame 2, and row [2] containing sub-frame 3. Data from the sub-frame is stored in a packed format, meaning that the 6 parity bits of each 30-bit navigation message word
have been removed, and the remaining 3 bytes are stored in 1.5 16-bit words. Since the first word of the sub-frame, the telemetry word (TLM), does not contain any data needed by the receiver, it is not saved. Thus, there are 9 remaining words, with 3 bytes in each sub-frame. This total of 27 bytes is stored in 14 16-bit words. The second word of the subframe, the handover word (HOW), has its high byte (MSB) stored as the low byte (LSB) of the first of the 16-bit words. Each following byte is stored in the next available byte of the array. Table 3-52 shows where each byte of the sub-frame is stored in the row of 16-bit words.
Note how there is the SV ID (2, 4, 9, 12, 15, 17, 28), then the MSB of the HOW (28 and does not change, naturally), then the LSB of the HOW which instead correctly increases by 4 (x1.5, as per GPS ICD, is 6 seconds, duration of a subframe) repeated three times each ephemeris.
Happy decoding!
Michele |
 |
|
|
Virgilio
Brazil
2 Posts |
Posted - 07 janv. 2012 : 18:19:09
|
Thank you, guys!
You helped me a lot Michele |
Edited by - Virgilio on 08 janv. 2012 02:53:18 |
|
|
| |
Topic |
|
|
|
| This page was generated in 0,33 seconds. |
 |
|
- 
- 
The meaning of each info in SIRFDemo .eph file
