Monday, November 24, 2008

Analyze Overall Curve Number with Map 3D

You can use topology overlays to create new topologies (intersections of, unions) based on properties shared between the two. Using this new topologies, you can do GIS analysis CN analysis for hydrologic groups and land use. Data from the topology overlay analysis can be used for an overall CN calc, etc.

There are a number of concepts to understand when using this procedure:

Map Cleanup Tools
SHP file import/export
Map Annotative Templates
Object Data

Topologies are prepared for each category -- watersheds, hydrologic groups, and land use.

The watersheds are delineated in Civil 3D.

The hydrologic groups topology is made by importing NRCS SHP files for soils. The hydrlogic groups is assigned by a variety of methods. The most simple way is to just enter the group in the object data via the properties toolbar for each polygon.

The land use topology is fashioned the same way as the other three. This topology will also have the uses assigned via the properties toolbar. A visibility dynamic block can help with importing features with a pull down menu. This data is exported with the "dataextraction" command and can be copied and pasted to the shape file of a dbf database.

The topologies are then overlayed. An object data table is created for each subsequent topology for assigned data from the relevant topogies. It helps to have seperate layer assignments for your topology linework, centroids, and annotations.

Two seperate overlays will need to be performed. More later...