Tutorial Notes – 04: Import streets (Part 2)



Maybe I’m just obtuse, but I had to read the “Grow minor streets” instructions on the tutorial several times to fully appreciate what they were telling me — so I will clarify it here.

We started by importing a street network from a DXF file. What we’re going to do is zoom in to a block of the street network (imported from a DXF file) where there are no roadways within. An example roadway is circled in red in Figure A below. Note that this is the only block in this diagram where an internal roadway exists. The instructions tell us to manually create two single small streets as shown by the red and blue dotted lines, using the Polygonal Street Creation tool, the center button on the inset at the upper right of Figure A. When you are through drawing the line, double-click to stop drawing.

Figure A: Drawing Streets with the Polygonal Street Creation tool (click to enlarge)

Now, look at the toolbar where the Polygonal Street Creation tool is still selected. When you use the “q” key, this will automatically turn off any tool you are working with and put you in select mode. You will see the button de-select when you do this.

Now we will select the segments we drew with CTL + left mouse button and drawing a square left and upwards. Be careful to select only what you drew and not any of the other streets or nodes; remember, there are different select operations based on which way you swipe the mouse. Go to Graph > Grow Streets, make your selections and click “Apply”.

The tutorial says the direction in which we draw our streets will specify “the general orientation of the streets in the block”, and you can see how this works in Figure B. Fair enough. But don’t expect streets to be consistently generated in the same areas. They may very well grow far outside the blocks on which you focused. When you select a street, note that other geometry outside your desired area may be selected as well, indicated by a blue dotted line that may be hard to see. All I can say is experiment.

Figure B: The direction in which we draw our streets will specify “the general orientation of the streets in the block”. (click to enlarge)

In the Street Widths section, the Tutorial notes “When importing OSM data with the Map OSM tags option enabled, CityEngine creates layer attributes that define street widths from OSM street types.”

What does this mean?

Click on the map layer and look at the Layer Attributes panel in the Inspector. The first line of the code says // Example OSM Tag Mapping. If you don’t leave the Map OSM Tags option checked, this code will not be generated. What difference does it make? If you want to change parameters globally for an entire category (class) of streets, modify the code and the streets will be redrawn. Zoom in on one of the secondary streets and change the code parameter from 7 to 12. The street will redraw as soon as you change the code.

Figure C: Changing the width parameters in OSM code mapping for secondary highways

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