Graphics Programs Reference
In-Depth Information
InfraWorks is georeferenced . This means it “knows” where it is supposed to be
on the earth. To make this possible, the coordinate information that makes up
the data refers to real places on the earth. For example, if you were to import
some GIS data that contained building outlines in the area where you live, the
x , y , and z (often referred to as northing, easting, and elevation) coordinates rep-
resenting the corners of your house would refer to real locations that you could
check with a handheld GPS or even your smartphone.
Sounds simple, right? Well, it would be except that there are many different
coordinate systems that are used to interpret coordinate data. To properly utilize
georeferenced data, you must ensure that the software is applying the proper
coordinate system so that the data is displayed in the correct location. Think of
it this way: If you were trying to translate a document written in a foreign lan-
guage, you would first need to know what language it was written in. Without
that, you cannot begin the translation. The same is true with coordinates and
georeferenced data. If you don't know the coordinate system (language) that the
data was “written in,” you cannot accurately resolve the data and ultimately put
it in the right place.
What makes coordinate systems different from each other? Lots of things—
too many, in fact, to cover in any kind of detail in this topic. But to give you
some idea of what is involved, here are a few basic factors that cause coordinate
systems to be different:
Location Imagine creating a single global coordinate system. Pick a spot to
call the origin, say the South Pole, and measure outward and upward in meters
or feet. By the time you got to New York, the numbers would be too large to
work with. That's why in some cases you will see coordinate systems represent-
ing small geographic areas. For example, in the United States, each state has at
least one coordinate system, and many are broken up into zones because even a
single state is too large to work with.
Information about
data is known as
metadata . When
you're trying to find
out what coordinate
system your data was
written in, you should
look for this word.
Projection Some coordinate systems aren't coordinate systems at all. For
example, latitude-longitude, which is designed to express location on a spherical
object, isn't a coordinate system because it does not use x , y , and z on a square
grid. Other coordinate systems use some tricky math to project part of a sphere
on a plane (an imaginary flat surface). Different coordinate systems can use dif-
ferent mathematical projections.
units I saved the easiest for last. Units of measurement are part of a coor-
dinate system too. In fact, for nearly every coordinate system you can find in
meters, you will also find its counterpart in feet.
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