Sight Distance at Existing Junction

This post is an update to a previous one on the same topic, this one is hopefully more complete.


We have an existing junction and we need to improve the sight distance.

You can use a number of methods to check whether you are getting the required sight distance along your sightline.


1. You can create a profile along the sightline and check the sightline against the existing ground surface and see where the obstruction occurs:

or 2. use the visibility tool 'Point to Point' to check.

These methods only provide an answer along a single line. We can see in profile the depth of the earthworks that needs to be excavated. It would be useful to be able to show the extent of the obstructed view area in plan and get an idea of the extent of earthworks that would be required to provide visibility. To do this we can use a combination of dummy corridors and surfaces to give us the desired result.

First create a profile along your sightline in plan sampling the existing ground surface. Next create a profile from your eye (height 1.05m) to your target (height 0.26m) - see screen grab below.

Next create an assembly using the LinkOffsetandSlope on the Generic tab of the tool palettes.

Create the assembly wide enough to cover the area of interest:

Create a corridor from your sightline alignment, sightline profile and the above assembly. Create a surface from the corridor using top links.

Next create a volume surface using the Existing ground as the base surface and the corridor surface as the comparison. Set the surface style to 2D Solid Level Banding or similar.

In the surface properties for the volume surface set the analsyis to Elevations, create one range and set the max value for the range to zero.

The result will highlight in plan the area where the drivers view is obstructed by the existing ground surface.

Found this useful? Need to learn more? Check out our Advanced Junction Design course HERE

Surface Triangulation max angle problem

One new feature added to surfaces for 2013 is the ability to specify a maximum angle between surface triangle lines. This is supposed to build surfaces more intelligently by removing triangles that exceed the maximum angle and result in less erroneous triangulation.


See the following link for more info:


http://beingcivil.typepad.com/my_weblog/2012/04/autocad-civil-3d-2013-new-features-check-tin-for-max-angle.html


This is intended to be applied to triangles that make up the outer boundary of your surface only. However, after creating a surface (style - Border Only) from some LiDAR data last week I noticed there were 'holes' in the surface. See below:

After some searching I checked the max angle and set this to 'No' and rebuilt the surface and the holes disappeared.

So it would appear that the setting is applied to internal triangles also. (which it shouldn't be according to the help menu)

Stage Storage

I have to thank the guys from Autodesk who showed this a few weeks back at the Autodesk Industry Academy in Amsterdam....

I used to think that this tool was related to the Hydraflow Storm Sewers application and therefore not relevant to this part of the world due to differing hydrologic design methodologies.

However this is a stand alone tool that is a really simple and effective way of calculating the volume of a pond. You can calculate from either a surface or polylines.

Run the command and you are presented with the following dialog box:

In here you can click on Define to add data to use in the calculation - you can choose either surfaces or polylines. I have had a number of crashes when using surfaces but am unsure of whether this is an issue with the command or my surface. The alternative is to extract contours from your surface first and then use these polylines in the stage storage command instead. You can also export a .txt report of the analysis or insert a table of the results into the drawing using the buttons at the bottom of the dialog.