Wednesday, October 31, 2007

Lines Merge

What's wrong with this picture? These two AutoCAD plots were made with all the same settings: Plotter, pen table, scale, etc. from the same drawing/same layers. However, the first image displays the lighting fixtures as bold and readable, whereas the second image shows the lights as obscured by the ceiling grid.
The only difference between the first and second plot is the order the entities were drawn in the database. In image two, the ceiling grid was placed last (or xreferenced last) and so is on top of the underlying light fixtures.

Can this be controlled? Can we force the light fixtures to show bold? The answer is a qualified yes.

For most plotters the default setting for Merge Control is Lines Overwrite. This means that the last entity placed in the database is plotted on top of other entities. At Benham, we typically change this setting on all of our plot devices to Lines Merge.This allows the bold, solid black light fixtures to "show through" the screened, gray ceiling grid.

Now for the qualification: not all plotter drivers have the Lines Merge ability; the DWG to PDF.pc3 for example does not. So now how does one make sure that the light fixtures plot bold and black when plotting to PDF? You're going to need to ensure that they're on top. Use the DRAWORDER command to send the ceiling grid to the back or bring the lights to the top.

Wednesday, October 17, 2007

The ByBlock Property

Here's a little tip that borders the edge of extreme AutoCAD nerd: the ByBlock property.

First, some background:

The default property for a new entity is the ByLayer property. This applies to the Color, Linetype, Lineweight, and PlotStyle properties. This means that the entity gets these properties from the layer on which it resides. If you move an entity to another layer, it inherits the new layer's properties.

You can override an entity's ByLayer property and give it an explicit value. For example you might select a line and make its color Green regardless of the color of the layer. Consider the following example. In the first image all entities are drawn on Layer A-WALL-FULL which has a Color of 2, Linetype of Continuous, and Lineweight of 0.35mm. The second image shows the same entities when moved to Layer A-WALL-JAMB which is Color 1, Ltype Continuous, and Lineweight 0.25mm. The last image shows what happens when the properties of the line are assigned explicitly.

Lost yet? Let's further complicate this by introducing nested entities, i.e., entities within blocks. If an entity in a block is created on layer 0, it inherits the properties of any layer the block is then inserted on. If the entities in a block are created on any layer other than 0, they retain the properties of that layer. If entities in a block are given explicit properties, they retain those properties regardless of the insertion layer.

And, finally, we come to the reason for this discussion, the ByBlock property! Let's draw some entities on layer 0 and make a block of them. We will leave all the entities of the block with the default ByLayer properties except for one entity. To this entity we assign a Color and Plot Style of ByBlock.

What's happening here? The first image shows the settings of the entities that make up the block. The second image shows this block inserted on layer G-ANNO-TEXT. Note how the entities within the block take on the properties of the layer. In the third image we select the block and change its Color to 8 and its Plot Style to 40 (which is 40% black according to our pen table). Notice that only the upper sweep changed. It was the only entity in the block definition that had a ByBlock property, so it alone took on the properties that we assigned explicitly to the block. The other entities had a ByLayer property and so retained the insertion layer properties. Also notice that the ByBlock property behaves just like ByLayer until you actually assign a property to the block.

All of the Benham title blocks were created to behave in this manner. So, no matter what layer standard or pen table are required by the project, we can still get the Benham logo to plot correctly by changing the properties of the block. There's never need to explode or redefine anything.

Tuesday, October 02, 2007

Layer Filter

Use Layer Property Filters to filter all the layers in your drawing to a manageable few.

Say you need to quickly set all the existing layers to a screened line plot style; a filter will allow you to display only those layers, and then you can make global changes. The Properties Filter button is found in the upper left corner of the Layer dialog.

Name the filter Existing, and enter the property criteria that will match only the existing layers, in this case we enter *-EXST under the Name property. (The star is a wildcard to match everything.)

Now use the Existing filter to limit the layer list to only those that end in -EXST. Select All and set the Color to 8 (gray) and/or the Plot Style to 40 (40% black) to get a screened line effect. You could also use this same filter to select the demolition layers for freeze/thaw or on/off.

You can use the same process to create a filter for -DEMO layers. You can even reverse this by creating a filter for new/proposed. Here's how: create a filter named not New and enter two lines for the name criteria, *-EXST and *-DEMO. The new filter will display only existing and demolition layers. Use the Invert filter in the lower left of the Layer dialog to show only layers that are not existing or demolition, making it in effect a not not New, or New, filter.

In these examples, the filter criteria has been the "Name" property, but you can also filter on other layer properties: color, linetype, lineweight, etc., or a combination.