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How to Reshape Contour Lines Using the Surface Model Editor in Basemap Plus
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By James Van Alstine
James is a geoscientist currently working in Houston Customer Support.
When a contour map is created through the gridding features of Basemap Plus, there are often odd kinks and bends in the computer-generated contour lines that would not have appeared had the contours been drawn by hand. Often, these odd shapes can be minimized or removed by simply changing the chosen gridding parameters, then re-running the gridding program. There will be times, however, when even after re-adjusting these parameters, the resulting contours will still not appear exactly as desired. The Surface Model Editor within the Gridding Menu of Basemap Plus allows you to edit, add and delete any posted contour set, grid or scatter set directly from the Basemap canvas.
When you select Gridding>Surface Model Editor, the Surface Model Editor window will open with a listing of all grids, contour sets, and/or scatter sets that you have posted on the Basemap. From this listing, select the item that you wish to edit and click OK. The Surface Model Editor will close and an editor appropriate to the selected item will open. For this article, we will focus on the Contour Editor option of the Surface Model Editor, which allows you to modify a selected contour set through a series of functions available from either the Contour Editor window or from the MB3 (mouse button 3) drop-down menu.
When the Contour Editor is opened, you will see that the displayed contour set is overlain by editing lines. These lines display all node points created along the contour lines during the gridding process. As you make changes to the contours, your changes will display only in these editing lines. The original contours will not be affected until your work is saved. This is accomplished in one of three ways: by selecting Done from the MB3 menu, or clicking on Save or Save As from the Contour Editor
Note: Save will save the changes to the current contour set, while Save As will save the contours to a new contour set.
Since no changes are committed to the database until you save, you have the freedom to edit your contours as much as you wish without the risk of losing your original work. Additionally, you have the ability to undo your changes while editing, using the Undo Last or Undo to Last Save buttons.
Note: Undo Last allows you to undo the last edit you made. Undo to Last Save or Undo All from the MB3 menu allows you to undo every change made since your last save.
Contour Editor functionality
Smooth existing contour lines
If your contour lines look good overall, but are a little jagged or angular, you can use the Smoothing Factor from the Contour Editor window to average out some of this jaggedness by a user-defined factor. To use this feature, enter a value into the Smoothing Factor text box (the default value is 3) and click the Select button from within the Contour Editor window. Essentially, the value for the Smoothing Factor is the amount by which the contour line will be smoothed. The higher the value, the smoother the resulting contour line will be. While in Select mode, click on a contour line with MB1, or hold down on the Control key and select multiple contours. The selected contours will then be highlighted in yellow. Once you have the desired contours highlighted, click MB3>Smooth to smooth the lines.
Delete contours or portions of contours
With the Contour Editor you have the ability to delete entire contour lines from a map or delete specified portions of contour lines. To delete entire contour lines, have the Select button turned on (red) and, while holding down on the Control Key, select the contour lines you wish to delete. Then, with the desired contours highlighted, click MB3>Delete to remove the lines from Basemap. If you want to remove only a specific portion of a contour, select Delete Area from either the Contour Editor or the MB3 menu. This feature allows you to define a polygon with MB1 around an area you wish to delete. Once the polygon is defined, click MB3>Break to close it. All contour points within the defined area will be highlighted. Then, as above, click on MB3>Delete to remove the selected contour lines from within the polygon.
Add new contour lines
If you wish to add new contour lines, or redraw deleted contours, select the Enter feature from the Contour Editor window or from MB3>Enter. Then simply start clicking with MB1 on the Basemap canvas to enter the desired contour nodes. While you are drawing the contour line, you should assign a proper Z value for the contour within the text box next to the Set Z Value button. To help determine a suitable Z value for the line, open a Supplemental Readout from User>Readouts and select the Grid Z and Horizon Z readout types. This will provide you with the Z value for any cursor location from the posted grid and/or horizon. This will not only give you the correct Z value for the Contour Editor, but can also act as an excellent guide for drawing the contour line accurately. When the contour is finished, click either MB3>Break to finish the line, or MB3>Close to join the two ends of the contour together as a polygon.
Edit existing contours
The Edit feature of the Contour Editor allows you to reshape, extend or connect any portion of your existing contours. With Edit selected from the Contour Editor, move your cursor over the contour line you wish to edit. The entire contour will become highlighted.
To extend the length of the selected contour, simply click with MB1 on the last node of the contour line and start clicking anywhere on the Basemap canvas to enter additional contour nodes. When completed, click MB3>Break to finish the line.
When extending a contour line, you also have the ability to connect it with other contours of the same Z value. To do this, extend your contour up to the line you wish to connect and place your cursor on the last node of that contour. If the Z values of the two lines match, the second contour will become highlighted. With the other contour highlighted, click on MB1 to connect them.
To reshape a contour line, you will need to first define the section of the contour you wish to edit. Click with MB1 on a node within the highlighted contour where you want to begin editing, then on a second node along the same contour where you wish to stop editing. The portion of the contour between these two points will be deleted, essentially breaking the contour line into two segments. The user will then be allowed to redraw the deleted contour segment using MB1. Once you have completed redrawing the contour, you reconnect the two segments by either clicking MB1 on the end node of the contour line or by selecting MB3>Join, which will rejoin the contour by filling in any remaining gap between the two segments with a straight line.
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