Autodesk 24108-051400-9000 - AutoCAD Revit Architecture Suite 2008 User Manual page 172

Parcel data in LandXML
COGO (Coordinate Geometry) Points
You can import LandXML COGO (Coordinate Geometry) points and convert them to AutoCAD points.
Civil engineers create COGO points to locate crucial surveying locations. A COGO point can be a project benchmark
point - a common datum that the entire civil team works off and from which all critical dimensions are located.
NOTE A LandXML file usually contains a large number of COGO points. In most cases, you need only a small set to work
within the drawing. You do not need to import all COGO points, only those that have a special meaning for the drawing.
COGO points are the foundation for any civil engineering or surveying project. In Land Desktop, you can use description
keys to place points in the drawing with symbols on specific layers. When importing a LandXML file you can map
selected points to the appropriate layer.
When a COGO point is imported it is defined by its coordinates in the form of northing easting" or northing easting
elevation."
For example, a COGO point could be represented as:
1.000000</CgPOINT>
COGO points on a map
NOTE Autodesk Land Desktop uses two coordinate systems for locating points: X,Y and northing/easting. When you start a
new project, these values all default to 0 so that the Y coordinate is the same as the northing, and the X coordinate is the
same as the easting. Unless you change that in Land Desktop before exporting a drawing to LandXML, the exported northing
value will be identical to Y and the exported easting value will be identical to X.
Surfaces
In most surveying and civil engineering operations, you gather information about elevations to generate surface contours
that represent a model of the ground surface. The surfaces in LandXML are made up of many faces which are either
TINs (Triangular Irregulated Networks) or quadrilaterals. Points or contours are usually a primary part of the original
surface information and are supplemented with break lines and boundaries. You can create a surface in LandXML, and
then import it. It is converted to a Free Form mass element.
In the following cases, importing surfaces can create errors or fail altogether:
Surfaces with vertical faces
Surfaces with tiny gaps between the individual faces
Surfaces with very narrow faces
If the import fails, an error message is displayed on the command line, such as Failed to create mass element from
terrain."
132 | Chapter 5 Interoperability with Other Applications
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<CgPOINT NAME="1" DESC="MYPOINT">248.04605951 359.53997314