Wednesday, 30 May 2012

Wind Farm Access Roads - Hardstand Area Design

The following post forms part of an article written for this month's edition of AUGI World magazine on using Civil 3D for designing wind farm infrastructure, pg 54.
Hardstand areas are constructed to provide sufficient space for the cranes to operate during erection of the wind turbines. The hardstand areas must be large enough for the cranes to operate in and also provide storage space for materials.

The hardstand areas are effectively a widened region on the corridor. Typically the hardstand areas are flat and widen at right angles to the corridor, see image below. This can cause problems when targeting the hardstand widen alignments using an assembly on the centreline alignment. Civil 3D targets perpendicularly from the baseline alignment and will not model the hardstands correctly at the widen region.
There are a number of methods for modelling this type of widening.
a)  You could add offsets to your assembly and use the offset alignment to provide the offset value. This method gives mixed results when the widening is perpendicular to the main alignment.
b)  You could also create a featureline defining the edge of the hardstand and then use the grading tools to model the earthworks – this has the advantage of correctly modelling the grading in tight corners where the corridor would otherwise overlap. The disadvantage is that you have a number of ‘parts’ to your model and increased margin for error.
c)  The third method involves adding the hardstand alignments as new baselines to the corridor and applying earthworks assemblies along these baselines. This results in one object (the corridor) controlling the earthworks thus reducing the amount of ‘parts’ in your model. This is the method that has given the best results and the one we are going to look at here.

Step1: Create Hardstand Alignments and Profiles:
Create alignments defining the left and right edge of the hardstand and then create profiles along these alignments. As mentioned above, the hardstand areas need to be flat - the profiles along the edge of the hardstands need to be at the same level as the centreline profile. To achieve this we will use a dummy corridor to provide levels along the hardstand alignments.

To create the dummy corridor first create an assembly that has 0% grade and wide enough to extend beyond the extents of the hardstand. The LinkOffsetandSlope generic subassembly works well, see below.
Next build a dummy corridor along the centreline using the assembly. See below.
Create a surface from the corridor and finally a surface profile along each of the hardstand alignments sampling the dummy corridor surface. This gives our levels along the edge of the hardstands.

Step 2: Create Hardstand Assemblies:
The hardstand assemblies will be applied along the left and right hardstand alignments. The left and right assemblies will consist of the left and right earthworks subassemblies used in the main access road assembly.

Create your new assembly. Select the earthworks subassemblies from the main access road assembly. In the case below I am selecting the ditch, conditional cut/fill and generic subassemblies used to model the earthworks for the left side of the road.
Copy these to your hardstand assembly and repeat for the right hand side. Your finished assemblies will look something like the following:

Step 3: Add Baselines and Set Corridor Properties:
Next add the hardstand alignments to the main corridor as new base lines. In the corridor properties add a region to each of the new baselines for the chainages of the hardstand.
Anyone who has used corridors to model earthworks in tight corners will know that the downside is that the corridors do not resolve the overlap on the insides of bends similar to the grading tools– see screen grab below.
To resolve this issue we can use a workaround. In the corridor frequency for the hardstand regions set the sampling frequency to a value greater than the total length of the alignment and set the additional sampling frequencies to ’No’.
This will result in no automatic corridor sampling frequencies being applied to the region. We will then add in sampling stations manually at points along the region ensuring there is no corridor overlap in the earthworks.
This will not result in a perfectly modelled corridor but the differences in terms of volumes calculations are tiny in the grand scheme of things. The benefits achieved by having one corridor where you can easily make edits and create surfaces for volume calculations far outweighs those of having a 100% perfect model.

Wind Farm Design - Creating Geological Surfaces from Probed Depth Values

This post forms part of an article written for this month's edition of AUGI World magazine on how to use Civil 3D for designing wind farm infrastructure, pg 54.

Creating Geological Surfaces from Probed Depth Values:
Probed depths or borehole logs provide us with information on the subsurface geological layers for the site. When importing and using this data in Civil 3D there are a couple of issues that need to be looked at.

Issue 1: The surfaces created from the depth values in Civil 3D are of limited use. What we really need are the elevation values at each of the probe locations.  We need to convert the depth values into elevations.

Issue 2: Due to differing surface data resolutions (typically more points in the existing ground surface) the bottom of peat surface may not appear to accurately represent the geological layer – it may not ‘follow’ the lie of the land. See screen grab below. (You could in some cases see your subsurface extend above the existing ground in section). We need to create a surface that uses the probed depths and also ‘follows’ the existing ground in the areas in between where we do not have any probes.
There is workaround that has previously been posted on a number of blogs and forums that solves both of these issues. Here it is described as applied to a windfarm project - with a little bit of explanation of what is going on in the background from a Civil 3D point of view.

  1. Create a TIN surface from your probed peat depths – call it Probed Peat Depth.
  2. Create a volume surface using the Existing Ground surface and the Probed Peat Depth surface – call it Peat Volume. The order in which you add the surfaces is important (base – Probed Peat Depths, Comparison – Existing Ground). You now have a volume surface that has depth values that are equal to the elevation for the bottom of peat.
  3. Create a new TIN surface and call it Surface from Peat Volume. Paste in the Peat Volume surface. Pasting a volume surface into a TIN surface creates a surface with elevations equal to the depth values of the volume surface– we now have a TIN surface representing the bottom of peat.
The surface created in step 3 uses the probed peat depth values and follows the existing ground in between probes.  Note – this is not a true representation of the sub-surface geology but it is a good base to start with.

Tuesday, 29 May 2012

Compare Drawings

The compare sheets tool in Autodesk Design Review is a great tool for checking for changes in geometry between different issues of a drawing. The tool only works on DWF files however. In my experience most people issue drawings in PDF format which meant the tool couldn't be used.

There is a workaround however. You can convert PDF's to DWF's using the DWF writer printer driver which you can download from the following link:

This will allow you to print to DWF from a number of document formats including PDF. Below is the print dialog box from Adobe Reader.

Thursday, 24 May 2012

Surface Analysis Precision

This bugged me a while back and I meant to post about it.

I created a volume surface to show extent of cut/fill along my access road - red for cut and green for fill. I used the 2D Solid Level Banding surface style from the AutoCAD Civil 3D 2013 UKIE drawing template. I set my no. of ranges in the surface analysis to 2 which picks up the min and max levels on the surface and divides the level difference into two ranges.
All going well so far until I click ok and look at my surface... which appears to have 'holes' in it.
So why was this happening if I set it to automatically divide the surface into two ranges? The answer is in the surface style settings. The range precision is set to 1 which meant the max elevation for range 2 in my surface analysis stopped at 1m when in fact it was greater than that.
Setting the precision value to 0.001 and rerun the analysis solves the problem. Max elevation for range 2 now corrected to 1.293m.
The holes in my surface are no more...
The surface elevation analysis appears to begin at the absolute lowest elevation (ignoring precision) and work up to the max value (precision applied) - whereas I had always assumed that it found the absolute min and max levels first and then divided the difference into the specified number of ranges.

Tuesday, 15 May 2012

Easy Access to Map 3D Commands in Civil 3D

One of the great things about Civil 3D is that it contains a whole suite of GIS tools in the form of Map 3D commands. These can be accessed by entering them at the command line if you can remember them. You can also access them on the ribbon by switching to the Planning & Analysis workspace.
If you need to use these commands as part of a Civil 3D workflow it can become a bit frustrating switching back and forth between workspaces. A more efficient way of working is to use the Map drop down menu (the menus that Autodesk keep hiding by default!). The map menu will provide you with quick access to the Map 3D commands in Civil 3D.

To display the Map menu follow these steps:

Type CUI at the command line and press Enter to open the Customize User Interface dialog box. 
On the Customize tab under the Customizations in All Files panel scroll down to and expand Partial Customization FilesRight click on Partial Customization files and select Load Partial Customization file.
Browse to the following file (Windows 7): C:\Users\USERNAME\AppData\Roaming\Autodesk\C3D 2013\enu\Support\MapClassic.cuix. Select Open. Click Apply and OK.

Finally to display the drop down menus in Civil 3D type MENUBAR at the command line and set the value to '1'. The Map menu should now be added to the list of menus at the top of your screen.

So for example I was using a lot of aerial photography in a recent project. Each image tile had a world file associated with it to enable it to be georeferenced to the correct location. To import the imagery and georeference the images using the info. in the world files you need to import using the Map image insert command rather than the normal AutoCAD image attach. This can be found easily on the Map drop down menu... nice and easy to access..
Using the Map drop down menu along with the map workspace (MAPWSPACE) gives you (easy) access to most of the Map 3D commands in Civil 3D.

Tuesday, 8 May 2012

Accessing Aerial Imagery in Civil 3D

The guys at Autodesk Labs have released a really cool and very useful new tool for Civil 3D and Map 3D. It allows you to connect to Bing Maps (Microsoft) from within your drawing and provides access to aerial imagery and road information quicker than I have ever managed to get it in there before! No messing around with world files or scaling and manipulating image tiles...

Below is a screen grab of my site before I connect to the mapping. There are a number of roads, existing dwellings and a railway running across the south of the site. All of this of course would be easier to make out if we had some aerial imagery. 
1.   To connect to the mapping you will first need to assign a coordinate system to your drawing. Type MAPCSASSIGN at the command line and search for your coord sys. Use a filter if you know part of it's name.
2.    The utility provides a new connection in the data connect tools. To open these tools type MAPWSPACE at the command line and then click on the Data Connect button in the dialog box that appears. This opens the Data Connect dialog box below. Highlight Add Basemap Service Connection and click Connect. this makes a connection via the internet with Bing Maps.
Select the data layers you want to add to your drawing and click Add to Map.
The information is added to the map within the limits of the coordinate system. It appears to use information from the coordinate system to run a query on the Bing Maps to determine the amount of information it pulls down to your drawing. This query will update if you change your coordinate system after you have connected. This is handy if you pick the wrong coordinate system initially, just re-run the MAPCSASSIGN command and choose the correct one -the mapping will update automatically.

You can use the layer controls to turn off some of the information. In my case I just want to see the aerial imagery. The large red circle I drew myself so I could locate where the project is.
The quality is pretty decent as you can see below... The only draw backs with this tool are that you cannot save the maps (Im not sure if this is that big of a deal though as you can print the information) and it is also only available on the Labs website until 30th June. Other than that this is a great new tool and a great direction for the software to be heading... The tool is called Project Basejump and its also free, download and test it out HERE
A good addition to this tool might be the ability to enter into street view from directly within your drawing. I have found street view very useful on previous jobs when you are back in the office after completing a survey. If some of the line work doesn't make sense or you cant remember what was happening on the ground at a particular point (and you haven't taken a photo!) - just use street view to refresh your memory. The only problem at present is that you have to jump back and forth between Bing maps or Google Earth and your drawing to do this... food for thought...