引用:
最初由 野豹子 发表
别说是中科院,只要是对新藏线认真了解的人,或者是真正走过新藏线的人,谁都知道是5320米.我是好心提醒你们,以免被老外笑掉大牙!现代科技这么发达,GPS卫星定位已是大众工具,误差只在10米以内.中科院的严谨复杂工作只是要解决5米以内的误差.6700只是当时的ZF故意编造出来的,或许是当时科技落后,或许是出于军事上的需要.现在别说是专业工作者,就是一般的旅行者都知道是5320米.所谓是无知者无畏啊!!!
当然到底有多高跟我们是没关系,有关系的是一个人的认真态度.如果别人怀疑你的为人,怎么会相信你写的东西,你拍的照片.
最重要的一点: 抱着你的无知和轻率,随意的闯入这片高原圣地,既是对生命的不负责任,也是对这片雪域净土的侮辱.
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因为红颜回了帖，我也再回你一帖，让大家看看什么才是无知！
你已经从“可怜的孩子”和“无知”上升到了我对“这片雪域净土的侮辱”，这帽子吓人哪！本来不准备回你的帖了，可是你既然提到GPS的误差在十米之内，我觉得有必要给你上一课，让你知道一下GPS的可靠性。
GPS只是对经纬度才稍准确些，说准确是因为有军用和民用之分。因为民用的GPS在频道和数据传输的时间差上的预先设定，误差有可能远不止十米，更何况你所在的区域是军事敏感地带，你真指望你车里带的GPS是顶头的几颗高精度军用卫星传给你的啊？一个GPS所需要的数据来自好几颗卫星，你要指望在边境线上得出准确的结果，不过是痴人做梦罢了！用民用的GPS测海拔高度，还满世界显摆要改教课书，还教训别人不严谨，真是让人开眼了！我看你也不像是做什么科研工作的，这就传一篇文章在下面，看看别人是怎么评论GPS和海拔高度的。看不懂英文也没关系，我把第一句和最后一句的大意翻译一下。有关GPS和海拔精确度的文章很多，要上网掐架，打得别人哑口无言，也得事先稍稍做点准备再来。否则真要让行家笑话，这算是我对你的忠告了！
引这篇文章是因为这家伙写得逗，也算是对另外想用GPS在边境线上得出不同数据而满世界嚷嚷的人作点参考。
“很多人在买了新的GPS后总是怀疑自己的GPS精确性。有的在看到他们的GPS上的海拔高度相差有好几百英尺的偏差后甚至会认为自己的GPS坏了。这是正常的！”
………
“不管怎么说，靠GPS来测海拔高度是很不可靠的，假如你想用你的GPS上所表示的高度来降落你的小飞机，那么请你事先一定买好足够的保险！”
New GPS buyers are frequently concerned about the accuracy (or lack of it) of the altitude readout on their newly purchased GPS. Many suspect their equipment may even be defective when they see the altitude readout at a fixed point vary by many hundreds of feet. This is NORMAL.
With most low cost GPS receivers, the horizontal error (without SA now that it is off) is specified to be within about +/- 15 meters (50 feet) 95% of the time. Most users find this is a conservative specification and that their modern GPS receivers routinely perform better than this worst case specification. But.. Users should expect that SOMETIMES they may see the error approach the specification limits. AND.. 5% of the time, the error may be "any value" from zero to whatever". Note: Unless you have a CLEAR AND UNOBSTRUCTED view of the sky (on your dash or looking out of an airplane window with no externally mounted antenna, or similar obstructed view does not count!) you can count on your error excursions to be much greater than the above numbers. Your GPS <depends> on this clear and unobstructed view or it cannot make accurate range measurements to the satellites.
Generally, Altitude error is specified to be 1.5 x Horizontal error specification. This means that the user of standard consumer GPS receivers should consider +/-23meters (75ft) with a DOP of 1 for 95% confidence. Altitude error is always considerably worse than the horizontal (position error). Much of this is a matter of geometry. If we (simplistically) consider just four satellites, the "optimum" configuration for best overall accuracy is having the four SVs at 40 to 55 degrees above the horizon and one (for instance) in each general direction N, E, W, and S. (Note: You will get a very BAD DOP if the SVs are at the exact same elevation. Luckily, this is a rare occurrence.) See: DOP demonstration site by Norris Weimer> How SV geometry affects GPS accuracy(Java Required).. The similar "best" arrangement for vertical position is with one SV overhead and the others at the horizon and 120 degrees in azimuth apart. Obviously, this arrangement is very poor from a signal standpoint. As a result, of this geometry the calculated solution for altitude is not as accurate as it is for horizontal position. Almost any calibrated altimeter will be more stable at reading altitude than a GPS.
GPS altitude measures the users' distance from the center of the SVs orbits. These measurements are referenced to geodetic altitude or ellipsoidal altitude in some GPS equipment. Garmin and most equipment manufacturers utilize a mathematical model in the GPS software which roughly approximates the geodetic model of the earth and reference altitude to this model. As with any model, there will be errors as the earth is not a simple mathematical shape to represent. What this means is that if you are walking on the seashore, and see your altitude as -15 meters, you should not be concerned. First, the geodetic model of the earth can have much more than this amount of error at any specific point and Second, you have the GPS error itself to add in. As a result of this combined error, I am not surprised to be at the seashore and see -40 meter errors in some spots.
DGPS operation (where available) will dramatically improve the performance of even low cost GPS receivers. Horizontal accuracy of +/- 5 meters and altitude accuracy of +/- 10 meters (relative to the WGS-84 geode) with suitable DGPS receivers and low cost GPS receivers such as the Garmin GPS-12XL can be expected.
In any case, it is extremely unwise to overly depend on the altitude readout of a GPS. Those who use GPS altitude to aid in landing their small plane should have their insurance policies paid up at all times.
Joe Mehaffey
