Got it. Flat.
And this is what scares me.
I have several Pixhawk based quads, from tiny 250 FPV with Bulgarian Pixhawk clone and old MT3329 GPS module up to the largest one based on S1000 frame with NEO-M8N, all with different GPS units, including old Mediatek MT3329, MT3339, LEO-6H, NEO-7 and the newest NEO-M8N on large round PCB from CSG store, and none of them never lost GPS lock in semi-open not even completely open space.
Never.
Average lock time is about 20 seconds when I fly the bird from one day to another, or up to 45 seconds, when the bird is off for longer time. As soon as the GPS module backup battery powering RTC clock loses power, typically after two weeks, it takes under minute to get perfect 3D GPS lock.
From my experiences I can judge whether bird GPS reception is OK or not, and always use simple cell phone check with S5/S6 to immediately confirm actual GPS situation at the moment on the site. Cell phone have much inferior GPS antenna to the quad GPS unit, so if the cell phone get lock and sats, bird shall as well.
Not to mention great sites like
http://www.uavforecast.com/ and
http://www.taroz.net/GNSS-Radar.html will tell you exact sats constellation above you.
Fresh from the 3DR board:
Greg Nuspel :
The GPS issue is caused by people who don't understand the nature of GPS signals.
How sweet.