randy: It's probably not a GPS issue byt rather a compass issue. Just yesterday I put together an Advanced Compass Set-up wiki page (http://copter.ardupilot.com/wiki/ac_compasssetupupadvanced/) which includes the "compassmot" feature which measures your compass interference. Could you try running Compass mot? There's a video (http://www.youtube.com/watch?v=0vZoPZjqMI4) on that page as well that runs through the details.
我觉得你讲的更有可能,我在DIYDRONE搜了一下,至少有5个人跟我的遭遇一样。我自制的机架因为调试GPS已经完全坏掉了,等我再制一个机架,就根据你说的,在源码里面找找参数,把它们全部清零。