Trimming polygons
Confutus
Newcomer
I'm trying to make a smaller map from a larger one, using the Mike Schley style. Following the Tome of Ultimate Mapping, I have successfully edited a major landmass with its coastline. However, contours are giving me trouble. These are (very irregular) polygons, and I want to delete the portions outside my smaller map boundary. Since the Trim command doesn't work on polygons, what's the best combination of commands that will do this?
Comments
Hello Confutus :)
Try using the Break tool Break
to make a small break in the contour anywhere outside the map, and then use trim on the resulting line.
The break and trim commands were giving me trouble and inconsistent results. First I had problems determining the proper break point, but I finally saw the note from the Tome that I need to select the line to break on a point I want to keep, which is the opposite of what I was expecting. Similarly for the trim.
I had some of my contours already filled in with shading, and the program had trouble determing whether it was the outline polygon (straight) or the filled shaded polygon (smooth), that I was trying to break, when the two share the same node points. So now that I've figured that out, I want to (of course) reconnect the outline and shading paths into new polygons at the new border. How do I do that?
As long as the two entities are on a different sheet, or a different layer from each other you should be able to isolate one set from the other.
I would work on one set at a time - for example the outlines only, or the polygons only, and hide the other set by hiding its sheet or layer.
For the filled polygons use extract properties before you start breaking them, and use it each time you start a new one. This will set the active properties to the particular properties of that particular polygon, including colour, so they will automatically return to the right colour once you close each one to a polygon again at the end of the operation.
Also, if you want to halve the time it will take you can delete the outlines and then recreate them by copying the filled polygons onto their sheet after the trimming job. Then use the Change Properties tool to set them back to outlined polygons rather than filled ones.
Thanks. I think I got it. There was only one filled polygon that extended beyond the new border, so I had to 1) convert the b-spline to a 2d polygon using explode: Smooth to straight, 2) do the break and the trim, 3) Use Draw: Path to Create a path along the new map border, 4) Use Edit: Transform: Combine paths to create a new polygon, then 5) use Explode: Straight to smooth to convert it back.
So for the remaining contour lines (which I had fortunately not filled in yet) I can do the same thing except the first and last steps.
You're welcome :)
I'm glad you managed to sort it out.