Generating Points From CAD

Generating Points from CAD to Create Models in ⁿ4ce

CAD is a generic way of displaying graphical data. It may be in 3D but is of little use to us unless we can convert it into a model. There’s little intelligence in CAD apart from unrelated elements having a style, colours and are located on a nominated layer. Blocks are a collection of CAD elements.

Models used in ⁿ4ce are drawn from a code table using a feature code.  They visually look the same as CAD, but that is where the similarity ends. The feature code is cross-referenced to the code table, which dictates how features will be plotted. Only the point is stored, and every other detail is generated on the fly. This means move, delete or change the code for points and everything attached to that point will be updated.

Being “intelligent” allows ⁿ4ce to recognise details and behave appropriately. For example, plotting height text long a feature. The code table specifies the text style, offset and orientation. When using the text editor, moving text becomes easier, like flipping all text to one side of a line or making text readable.  A filter option allows overlapping height text with a lower priority to be removed.

So how do we take a CAD drawing and make it into an intelligent model?

Importing CAD into ⁿ4ce

There is a special branch on the Project Tree where you will import/create and store your CAD files.

Importing CAD Data

CAD files can be imported in various formats including AutoCAD^TM (DXF, DWG, DWT), AiC DOT files and OS Mastermap^TM GML files. You can of course create a new empty CAD folder.

Having identified the file you wish to import, you will be invited to enter parameters relating to this file.

CAD General Parameters

Whilst we are compatible with AutoCAD in most respects there are several things you need to be aware of.  Firstly, AutoCAD draws text in ground units whilst ⁿ4ce uses text styles with units of mm, at a reference scale. Text remains the same size in ⁿ4ce irrespective of the plotting scale. You will be required to provide the appropriate scale when importing and exporting to and from AutoCAD file formats.  Next, be aware that some drawings may be in mm (Architects) so you must identify this on import otherwise your models will be scaled up by 1000x.

Once imported you will see the available CAD layers in the display window.  Max and Min XY coordinates for each layer will be shown together with a flag to indicate if the layer contains 3D elements.  Whilst the display will be in 2D, data is stored in 3D.  If appropriate a Y will appear in the 3D column.

The status of CAD layers can be changed and viewed independently, to identify their contents.

Displaying CAD Layers

By selecting the appropriate CAD folder and a camera icon, you will enter the CAD editor, as shown below.

ⁿ4ce Cad Editor

Inserting Points in a Model from a CAD Backcloth

As previously discussed, you need points in a model to form a DTM from which contours, sections and volumes can be calculated.

The starting point here is to isolate the layers that contain detail you can use to generate these points.  This can be done in the project or CAD editor .  The Show icon in the editor, used in conjunction with the layering icons   is useful here.

Isolated CAD layers

 The next stage is to introduce this CAD folder as a normal backcloth to a model. Note that layers of backcloths can be controlled through this dialog.

Selecting a CAD Backcloth – Note Layers Button

CAD Backcloth to a Model

Before we investigate the option to generate points from CAD lets look the Points\Insert option.

Inserting Points using Indicated Text

Here we have a Height Calculation option called Indicated Text.  This allows you to select height text from a CAD backcloth.  But make sure you know what you are identifying. For example, here we have points in the CAD backcloth that are symbols. When indicating the location, by Sketched, it is important to set the lock mode to Symbol.

Whilst on the issue of using height text from CAD backcloth, there is also an option to identify CAD text in the move options.

Moving Height to a CAD Text Label

Automatically Extracting Points from a CAD Backcloth

Whilst the Insert and Move methods described earlier are ideal for small number of points, it can be very time consuming when large amounts of data are involved. The option to use here is Points - Generate and the set up is indicated above, using a CAD backcloth first.

Note:  Be selective on active CAD layers.  DON’T convert all Elements you see into points as there will be a lot of editing to do!

Generate Points from CAD Menu

Individual CAD elements can be selected, or all Element types.  There are also options for adding multiple points along Lines, Arcs and Contours. We’ll explore a few of the options available here, starting with Symbols.

Firstly, isolate the layer containing the detail you’re interested in. Here we have separated the CAD points from all other detail and they’ve been identified as 3D symbols (blocks). This is not always the case, and you may be left wondering how to attach a height to these points.

The Pick options of Element, Rectangle and List can also be used to select the CAD detail you wish to generate points from.  If you are using single Elements, simultaneously use the Lock options to ensure you’re picking the correct points. Most likely you will be using the Rectangle Pick option.

After sweeping a rectangle (pick) over the CAD detail you will be presented with a dialog box similar to the following.

Generating Points from CAD Symbols

The first column identifies how the height of the new points will be calculated, with Assigned being used if the CAD detail is in 3D. The option Closest Text can be used for 2D detail, and searches for CAD text in the vicinity of the new point.  If the CAD text contains alpha characters these will be ignored, and the remaining number used.  Eg IL 23.45mAOD. When two numbers appear in the CAD text, only the first will be used.

The Parameters panel allows setting of a Code and String Numbers are allocated.  The Options panel provide further choices, including checking for duplicates and taking the code from the layer name.  Other non-applicable options are greyed out here.

Let’s have a look at generating features from CAD lines.  The options here include from lines, along lines and contours. The latter may be useful if you have 2D lines but a contour text value close by.

Generating Points from CAD Lines

There are several settings here, including how heights are assigned, but we will look at Options.

• Layer is a Code - This function is where the CAD folder is structured so layer names are the feature code of detail stored on that layer.
• Prefix Created Points – will add a G to the point number of points created.
• Check Duplicates – This function removes any points that are duplicated.
• Filter Along Lines – This option will both smooth out features and remove redundant points along lines, using an algorithm called Douglas Peucker. It works by calculating the offset of the middle of three points and comparing this to the Filter Offset.
• Trace Lines – can be used to link individual line segments to make continuous features.
• Trace Tolerance – allows the ‘touching’ tolerance to be set for segmented lines.
• First Point Only – identified the first point on a line feature. Remember lines are directional.
• Midpoints Only – Finds the midpoint of segments. Levels are linearly interpolated between endpoints.

Points can be added to the List for further processing.  Additional options are available for circles and arcs.