Monday, May 04, 2009

Back to Basics – Alignment Line Entities

When creating an alignment you have the option to create it using Layout Tools. I find this methodology is a tad bit different than LDT where you created alignments primarily from polylines. It takes a little while to get used to how to use the tools. This post will cover how to the line entities work.

The first concept that needs to be know is what in the world Fixed, Floating and Free mean. I personally had a hard time learning the concepts because my preconceived notions where backwards. The term Fixed indicates that entity is not dependent on another alignment entity, it exists wholly on its own. The term Floating indicates that one end, usually the beginning, is dependant on another alignment entity. Free indicates that the entity is tied other alignment entities on both ends. I think the terms should be switched since, but I won’t get into that to avoid confusion.

Fixed Lines


The first one’s pretty easy. Indicate the length of the line entity by two points. The video below shows the fixed line in action.

The next one is a Fixed Line (From curve end, length). This draws a line tangential from a curve a certain length. I don’t particularly like this one since the line will NOT stay tangential to the curve. Unless I’m copying an existing alignment I won’t use this one for design work.

The last fixed line is Best Fit. This would be used if you had survey data and where trying to find the best place to put a straight line through some survey shots. You can also use other entities to create the segment such as COGO points, entities, AutoCAD points or clicking on the screen. In this short video I use AutoCAD points. Once the data is collected you can process how the data is used in Panorama.

Floating Lines


The first floating line type is defined from an alignment curve entity through a point. The point you want to use has to be mathematically possible otherwise you will get an error symbol. The line will stay tangential to the curve if the curve or the line is modified.

The Floating Line (From curve end, length) creates a line that is tangential from a curve end and extends a specified length from the end of the curve. The line and curve will remain tangential.

Floating Line – Best Fit is similar to the Fixed Line – Best Fit, but will stay tangent to the entity selected. The video example below uses AutoCAD points.

Free Line

A free line spans between two alignment curve entities. The video below shows the free line alignment entity.

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