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# What's the difference between FLOAT and FIXED?

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Posts: 9232
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(@nate-the-surveyor)
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Fixed Integers, or Estimated integers? What is the practical explanation, and what is the technical explanation?

I felt that a good discussion of this would be helpful to anybody, who involves themselves in RTK GPS. And, Post processed, Static.

Nate

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(@dave-karoly)
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Posts: 9232
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(@nate-the-surveyor)
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(@foggyidea)
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I'm with Dave on this. I was going to say a couple of feet.

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(@stephen-calder)
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There are radio waves sent out from each satellite. Each wave has a 19cm wavelength. The phase center of your receiver antenna is close to one of the many possible intersections of the tops (or bottoms) of all of the satellite's wavelengths.

A fixes solution means that the software has determined that statistical checks on the data are within a certain tolerance that indicate that it is very likely that it has correctly chosen the intersection of wavelengths that your receiver antenna was nearest to.

Float means that the statistical tests did not return that certainty. It is still making a determination, but the tests did not meet a certain tolerance, and it could be wrong.

I used to think that only fixed was good, and float was for pikers, hayseeds, and shavetails. Now I realize that the receiver antenna is almost certainly NOT at the intersection, but merely near it, and given enough time, a float solution should actually be superior to a fixed solution.

But, this only for certain applications. For most GPS surveying, such as collecting topo and planimetric with a roving rod, you want fixed.

Stephen

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