Sirf III芯片gps的漂移问题

Sirf III芯片的蓝牙gps是现在的主流，最新的高明60csx也采用了这个芯片，这个芯片的信号接受能力非常好，我在户外一直使用蓝牙gps+智能手机+smartcongps，配合GM+OZI软件，效果也比较好。

在上月底，在三尖的路上，手机上使用支持矢量地图的smartmap，在大比例的地图上发现漂移的非常厉害，我们本次路线和以前的记录的轨迹几乎没有重合过，都有30-60米的差距，后来在：http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=25575
得到关于STATIC NAVIGATION的相关说明如下

While most settings are best left untouched unless you want to experiment (always risky !), "Static Navigation" is one that should be looked at closely especially with the arrival of the new SiRFstarIII based receivers, as these ultra-powerful receivers take GPS reception to a new level and can work with very weak signals but when that happens, accuracy can be impacted. Observations over a 24 hour period show that with good signals, 95% of the positions reported by the GPS will be within a 15 meter radius, while with weak signals, 95% of the positions will be within a radius of 50 meters.

Current road navigation software is designed for GPS receivers that only operate with good signals so accuracy will be in the 15 meter area. Such software will "snap" the position to the closest road so in a dense urban area, with degraded accuracy it's going to be easy to make the wrong decision and produce "uncosmetic" results and possibly force a trip recalculation.

Instead of redesigning navigation software to take this account (one could imagine some type of dynamic filtering based on DOP) and risk increasing the processing load on the PDA and hurt user experience, the easy fix is to implement this fix directly by having GPS manufacturers activate "Static Navigation" by default and therefore freeze the position using some complex algorithms mainly speed dependent. The problem with this is that this will considerably hurt low speed pedestrian use, with the speed staying on "0" and 50 meter jumps (update threshhold). If you want to use your GPS receiver outside your car, you'll need to disable SN,

就是说sn这个算法是适合汽车导航，如果是户外这类低速运动，是需要关闭这个功能的，不过一般的蓝牙gps没有相应的硬开关，可以使用SiRFdemo关闭，但重新开机后又会打开（据说holux的是默认关闭的，但我在厂商网站和说明书上都没看到说明），在ppc上有很多相应的软件可以关闭的，例如 MMSirfSetup。

而同行朋友的的60csx大概有90%的重合，应该手持机在天线和电路上的设计等功能帮助达到这个效果的，从这个意义上而言，蓝牙gps的还是差距很大的，希望关闭sn能对漂移有所改善。我们将在下次活动中记录关闭和非关闭，以及手持机的航迹，来比较确认最后的效果。

周游人 wrote:
Sirf III芯片的蓝牙gps是现在的主流，最新的高明60csx也采用了这个芯片，这个芯片的信号接受能力非常好，我在户外一直使用蓝牙gps+智能手机+smartcongps，配合GM+OZI软件，效果也比较好。

在上月底，在三尖的路上，手机上使用支持矢量地图的smartmap，在大比例的地图上发现漂移的非常厉害，我们本次路线和以前的记录的轨迹几乎没有重合过，都有30-60米的差距，后来在：http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=25575
得到关于STATIC NAVIGATION的相关说明如下

While most settings are best left untouched unless you want to experiment (always risky !), "Static Navigation" is one that should be looked at closely especially with the arrival of the new SiRFstarIII based receivers, as these ultra-powerful receivers take GPS reception to a new level and can work with very weak signals but when that happens, accuracy can be impacted. Observations over a 24 hour period show that with good signals, 95% of the positions reported by the GPS will be within a 15 meter radius, while with weak signals, 95% of the positions will be within a radius of 50 meters.

Current road navigation software is designed for GPS receivers that only operate with good signals so accuracy will be in the 15 meter area. Such software will "snap" the position to the closest road so in a dense urban area, with degraded accuracy it's going to be easy to make the wrong decision and produce "uncosmetic" results and possibly force a trip recalculation.

Instead of redesigning navigation software to take this account (one could imagine some type of dynamic filtering based on DOP) and risk increasing the processing load on the PDA and hurt user experience, the easy fix is to implement this fix directly by having GPS manufacturers activate "Static Navigation" by default and therefore freeze the position using some complex algorithms mainly speed dependent. The problem with this is that this will considerably hurt low speed pedestrian use, with the speed staying on "0" and 50 meter jumps (update threshhold). If you want to use your GPS receiver outside your car, you'll need to disable SN,

就是说sn这个算法是适合汽车导航，如果是户外这类低速运动，是需要关闭这个功能的，不过一般的蓝牙gps没有相应的硬开关，可以使用SiRFdemo关闭，但重新开机后又会打开（据说holux的是默认关闭的，但我在厂商网站和说明书上都没看到说明），在ppc上有很多相应的软件可以关闭的，例如 MMSirfSetup。

而同行朋友的的60csx大概有90%的重合，应该手持机在天线和电路上的设计等功能帮助达到这个效果的，从这个意义上而言，蓝牙gps的还是差距很大的，希望关闭sn能对漂移有所改善。我们将在下次活动中记录关闭和非关闭，以及手持机的航迹，来比较确认最后的效果。

奇怪，我用SIRF III的蓝牙GPS，重复的很好的啊。
有次去爬山，先下载了别人记录的轨迹，然后我就抓着GPS循迹，几乎是踩着他们的脚印前进的。