hi developers!

some times ublox modules when cold start 

reports "3D fix" with  high error - with hdop = 4.0

this mean accuracy +/-1km around real point.

before each fly with ublox module i check home position and reset APM when it incorrect.

in arduplane code after 5 first fixes point stores as home. if in this time hdop  > 2.0 it may be incorrect

this problem fixed in arducopter firmware using parameter

// @Description: GPS Hdop value below which represent a good position. Used for pre-arm checks

GSCALAR(gps_hdop_good, "GPS_HDOP_GOOD", GPS_HDOP_GOOD_DEFAULT)  

in arduplane.pde row 1017

 if (g_gps->new_data && g_gps->status() >= GPS::GPS_OK_FIX_3D)

maybe need change it to 

 if (g_gps->new_data && g_gps->status() >= GPS::GPS_OK_FIX_3D && g_gps->hdop < g.gps_hdop_good)