take the edge off Survey, GIS

I’ve just come from a conference where I was reminded of a Survey Feature that we often forget to show off in presentations - the functionality and options available in Civil 3D to create Points manually.

The scenario is that an intersection has been surveyed and the point where the 2 CL’s meet has not been picked up. The solution is to interpolate the Point from the Main road and join it to the Side Road (the dashed blue line above) so the triangulation forms properly.

This is just one of the options available in the Points > Create Points toolbar. Once you know the general gist of one of them…

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Why is this necessary?

Without the interpolated point, the triangulation goes straight across the side road ignoring the crest (see the image on the left).

When the Point is inserted, the string for the side road (CL02) can be extended so that the triangulation is formed correctly as in the image on the right.

There are times when the original triangulation will do the job fine but if the side road is coming in at a steep downward grade, the interpolated point will be critical.

How to create it?

Go to ‘Points>create points interpolate>interpolate’ or use the points create toolbar to get to the same function (I’m a fan of the points toolbar).

Use the ‘node’ OSNAP to select the points. Civil 3D displays the point elevation and prompts you to specify the desired level for the interpolation.

So,

• Click the Interpolate by Relative Location function
• Select (node snap) Point 1 for the ‘first control Point’, accept elevation 63.22
• Select (node Snap) Point 2 for the ’second control Point’, accelt elevation 63.95
• For Distance, graphically select the location for Point 3
• For Offset leave it at 0

Point 3 is created with the elevation 63.51 interpolated.

More..?

There may be a little bit of triangle adjustment to perform after this (flip faces or add breaklines) to correct the orientations. If you have stringer, just use ‘CL02′ as the description for the new point and it will become part of the side road string.

Don’t Forget: This is just one of the options available in the Points > Create Points toolbar. Once you know the general gist of one of them, it is not too difficult to work the rest out.

Also, this exercise is a relatively simple example - we were just putting a point at the end of an existing string - it gets more interesting when we want to insert the point into the middle of a survey string as the point number sequence may get confused.

More to follow,
cheers,
SeanT