gps

We are contemplating putting in a permanent base on top of the roof of our building. The top of trees on two sides of our unit are at about a 20 degree from where we plan on setting the base. The remainder of the sky is wide open. Would the trees on the two sides of the base introduce too much...

After comparing measured coordinates for multiple stations in the area to the NGS published coordinates of these stations, I am consistently getting 0.06 to .12 feet between the two values which seems great. However, I was wondering what is being held to establish these measured coordinates. Is...