One reason for routinely launching GPS satellites is simply "constellation replenishment," said Col. Andrew Menschner, deputy commander of the Space Force's Space Systems Command. Old satellites degrade and die, and new ones need to go up and replace them. At least 24 GPS satellites are needed for global coverage, and having additional satellites in the fleet can improve navigation precision. Today, there are 31 GPS satellites in operational service, flying more than 12,000 miles (20,000 kilometers) above the Earth.
Зеленский сделал заявление о ПутинеЗеленский заявил, что готов встретиться с Путиным на нейтральной территории
，这一点在WPS官方版本下载中也有详细论述
You look at a region of the image. If all the pixels are roughly the same color (below some threshold), you store the average color for the whole region as a single value. If the pixels vary too much, you split the region into four quadrants and try again.
The journey home took 17 hours.