Surfer 13 New Feature Series: New Geoprocessing Commands

Today's blog post focuses on new geoprocessing commands available in Surfer 13! Six new commands have been added to aid in creating, editing, and analyzing boundaries:

• Create Intersection Points
• Break Polyline at Intersections
• Difference of Polygons
• Intersect Polygons
• Union Polygons
• Buffer

Each of these commands can be found by clicking the Geoproccessing menu, and some of the commands are located in the Edit Boundaries submenu within this menu. Let's take a look at what each command does!

Create Intersection Points

Select multiple objects and click the Geoprocessing | Create Intersection Points command to create a point at each place the selected objects intersect with one another. The objects are not modified, and points are added at each object intersection. This command can be used with any combination of polylines, spline polylines, polygons, rectangles, rounded rectangles, and ellipses. The image below shows drawn objects before and after clicking the Geoprocessing | Create Intersection Points command.

Drawn objects before and after clicking the Geoprocessing | Create Intersection Points command.

Break Polyline at Intersections

The Geoprocessing | Edit Boundaries | Break Polyline at Intersections command breaks selected polylines and spline polylines at every intersection with another object, including other polylines and spline polylines, polygons, rectangles, rounded rectangles, and ellipses. Only the polylines and spline polylines to be broken need to be selected; it is not necessary to select the other objects with which the lines intersect. When the lines are broken, new polyline objects are created and added to the Object Manager; the original line no longer exists. The properties of the original line are applied to the newly created lines. When a spline polyline is broken, the resulting lines are converted to polylines. The image below shows the plot and Object Manager before and after clicking the Geoprocessing | Edit Boundaries | Break Polyline at Intersections command. After using the command, I modified the line colors to better distinguish them.

Before and after clicking the Geoprocessing | Edit Boundaries | Break Polyline at Intersections command.

Difference of Polygons

The Geoprocessing | Edit Boundaries | Difference of Polygons command creates new polygons that omit the overlapping areas in the original polygons. If the selected objects do not overlap, the objects are duplicated. The Geoprocessing | Edit Boundaries | Difference of Polygons command can be used with polygons, rectangles, rounded rectangles, and ellipses. Activating the command opens the Difference of Polygons dialog, which gives you the opportunity to specify whether the original objects are kept or removed. Check the Keep original objects option in the dialog to keep the original objects in addition to creating new objects that do not contain overlapping areas. If this option is not checked, the original objects are removed when the new objects are created. I've used the same example objects below, but I've reduced the opacity to better see the overlap. I chose not to keep the original objects.

Before and after clicking the Geoprocessing | Edit Boundaries | Difference of Polygons command and specifying not to keep the original objects.

Intersect Polygons

The Geoprocessing | Edit Boundaries | Intersect Polygons command can be thought of as the inverse of the Geoprocessing | Edit Boundaries | Difference of Polygons command. While the Geoprocessing | Edit Boundaries | Difference of Polygons command creates new polygons that omit the overlapping areas, the Geoprocessing | Edit Boundaries | Intersect Polygons command creates a new polygon from the overlapping area. The overlapping area must include portions of each selected object in order for a new object to be created. If the selected objects overlap in multiple places, a complex polygon is created. Click the Geoprocessing | Edit Boundaries | Split Islands/Lakes command to break the complex polygon into multiple polygons. This command can also be used with combinations of polygons, rectangles, rounded rectangles, and ellipses. Activating the command opens the Intersect Polygons dialog, where you can specify whether or not to keep the original selected objects. In the image below, I chose to keep the original objects, and I colored the new polygons with blue fill.

Before and after clicking the Geoprocessing | Edit Boundaries | Intersect Polygons command and specifying to keep the original objects.

Union Polygons

Selecting multiple objects and clicking the Geoprocessing | Edit Boundaries | Union Polygons command creates a new polygon by combining the selected objects. This command can be used with any combination of polygons, rectangles, rounded rectangles, and/or ellipses. You can specify whether or not to keep the original objects in the Union Polygons dialog after the command has been clicked.

Selected objects that do not touch or intersect will result in a complex polygon, similar to the Geoproccessing | Edit Boundaries | Combine Islands/Lakes command. Sometimes selections made up of many contiguous objects, for example states or provinces in a country, have objects that do not completely touch or intersect. If objects do not touch or intersect along the entire border, the Union Polygons command results in a complex polygon with small lakes. To remove the lakes, use the Geoproccessing | Edit Boundaries | Split Islands/Lakes command, and then delete the interior polygons. Alternatively, use the Geoprocessing | Reshape command to delete the vertices for the lakes.

This command differs from the Geoproccessing | Edit Boundaries | Combine Islands/Lakes command. With the Geoprocessing | Edit Boundaries | Union Polygons command, a new polygon is created from the selected objects. With Combine Islands/Lakes, the selection is combined into a single complex polygon. The original objects become islands and lakes, and a new polygon is not created. You can read more about the differences in the commands in the Surfer help. To access the help, click the Help | Contents command. In the help, click the Contents tab and then navigate to Surfer 13 | Editing | Geoprocessing Commands | Union Polygons.

The image below shows the counties in the state of Tennessee before and after clicking the Geoprocessing | Edit Boundaries | Union Polygons command to group them into the grand divisions of East Tennessee, Middle Tennessee, and West Tennessee. I chose to keep the original objects, and I also removed some extraneous lakes that remained after clicking the command by using the Geoprocessing | Reshape command. I filled each new polygon with a new color and increased the line width for the new polygons.

Plot before and after clicking the Geoprocessing | Edit Boundaries | Union Polygon command.

Buffer

The Geoprocessing | Buffer command will create a new polygon around or within selected objects at a specified distance. Any combination of points, polylines, spline polylines, polygons, rectangles, rounded rectangles, and ellipses can be used with this command. A polygon is created around all the selected objects. When the command is activated, the Buffer dialog gives you the opportunity to specify whether buffer polygons that overlap should be combined into one polygon (like when using the Union Polygons command) or if the polygons should remain individuals.

Additionally, the Buffer dialog lets you specify the number of buffers to create and the distance for the buffer(s). If more than one buffer is specified, the first buffer will be the specified distance from the object, and the next buffer will be the specified distance from the previous buffer. Polygons, rectangles, rounded rectangles, and ellipses can also use negative buffer distances. Negative buffer distances will create a new polygon within the selected object, rather than around it. For objects in a base layer, the units of the layer are used. If objects exist outside of a mapframe, the buffer distance is in page units (inches or centimeters).

I've added several buffers to the plot below. I added a buffer with a negative distance to the rectangle, a buffer with a positive distance to the polyline, and two buffers to the ellipse and rounded rectangle, with overlapping polygons specified to be combined.

Plot before and after clicking the Geoprocessing | Buffer command.

Whether you're trying to find the length of road between two cross streets, grouping together areas in a sales territory, or planning a boundary around a lake, I hope you find the new geoprocessing commands useful!

Do you have any questions about this post? Do you have an idea for a blog post or have a topic you'd like to see featured? Let me know! Leave a comment, or send an email to jennifer@goldensoftware.com.