Saturday, February 26, 2011

Geological Society of America References Style for BibTex

I hunted around long enough for a GSA BibTeX style, and I found one.  Direct link to .bst.  It appears to work well enough for my class papers.  Thanks to the Journal of Cave and Karst Studies!

I'll be keeping my copy safe.

Wednesday, February 23, 2011

Geologic Cross Sections and Adobe Illustrator

Last academic quarter, I spent time trying to understand how to easily remove vertical exaggeration (VE) from tabulated elevation and distance data in Adobe Illustrator.

Adobe Illustrator has a chart tool.  It isn't very robust or powerful.  In fact, it can be a pain to work with.

However, there is a way to manipulate its initial size such that (hopefully) VE = 0.

Perhaps you have found a better way? Here's my final solution.
  1. Import the data into a temporary scatter plot and take note of its automatic maximum vertical and horizontal tick values.  These values seem to be consistent no matter how you size the chart area.  Delete it.
  2. Take those maximum values and convert to the scale that you need to use (e.g., 1:24000) 
  3. The final two numbers should be in units of your artboard
  4. Create a new scatter plot chart but taking care to snap its size to your determined horizontal and vertical map distances using snap guides
  5. You should have VE at or near zero; verify this!
  6. Configure your chart: remove point markers, set line weights (tricky...), etc.
  7. Select your chart and ungroup it.  Yes, you do want to destroy the ability to change graph data because you'll really want to modify your new profile graph!
  8. See "Coloring Cross Sections: Adobe Illustrator Paint Groups" for what to do next.
This method hinges on the assumption that the drag box is exactly where your data will show up, with the axes coinciding or just barely exterior to it.  It may not be the best assumption but it seems to be the case.  Be sure that all the ticks are equidistant and there are no distortions on the axes.

In an ideal world, we would scale elevations and horizontal distances to artboard distances.  Then, import and plot the points so they automatically coincide with the units of the artboard WITHOUT using the chart tool.  This would remove the guesswork... is it possible?


Sunday, February 13, 2011

Measuring Lengths of Many Lines in Illustrator CS5

When balancing a cross section, you may need to know the lengths of beds between your pin lines.

Adobe Illustrator does not make this process obvious, and the built-in measure tool can measure only one line segment at a time.

To find the lengths of a group of lines (grouped or selected), turn on the Document Info dialog using the Window menu.

Select the options drop-down menu (the icon looks like justified text) on the upper right-hand corner of the Document Info dialog.  Select Objects.

Now you'll have the nitty-gritty details about your selected path(s)!

This could also be useful for measuring distances on non-georeferenced raster maps (with an absolute scale) by using a series of line paths. 

Thursday, February 10, 2011

Balanced Cross Sections Made Easy with Illustrator CS5's Smart Guides

Should you ever find yourself needing to professionally draft a balanced cross section, you may want to try Adobe Illustrator.  Under the Smart Guide preferences, you can customize the angles that lines snap to (so long as you have snapped the beginning node to another node, I think).

Sometimes Smart Guides has a difficult time snapping to angles if you start drawing a line without attaching it to an anchor. One thing that you can do is define the angle using the line dialog.  The other may be to draw a boundary line at the margin of the cross section.  Or, they just won't snap... and I have no idea why.  The Mac version of Illustrator seems rather inconsistent with its functions, at times.

But once you get past that initial point of setting up a line, Smart Guides is usually content snapping between lines that represent dip domains (angles that bisect between dip domains).  Remember, by default, smart guide activity is symbolized with a green line.

Once you've balanced a cross section, use the measure tool to make sure bed thicknesses and angles come out as expected.  It's pretty slick stuff.
30 and 60 degree angles automatically snapped between bisectors of dip domains.


So much for the protractor.

Monday, February 7, 2011

OSXStereonet 1.0.0 Released

N. Cardozo and R. Allmendinger has released a brand new version of Stereonet called OSXStereonet.  With a new name, this release is version 1.0.0.  It makes use of modern OS X interface and display frameworks.  You can now export to EPS and PDF.  In fact, you can drag and drop your stereonet plots onto the desktop.  Nice.

The software makes use of the Inspector interface, doing away with the Preferences menu.  In the Inspector you can set how the stereonet displays, tweak symbology,  and adjust Kamb contour parameters.

In addition, data now plots as you enter them within a brand new data editor interface.  Results for calculations are detailed in another panel.  You can load multiple datasets and turn them on and off at any time.

The data file format has changed slightly though older data format from the previous generation of Stereonet should import.  However, I had issues with importing trend and plunge with the plunge and quadrant format (trends didn't show up) I used for Stereonet 6.3.3.

This looks like a slick release!

Saturday, February 5, 2011

The Strain Ellipse and Adobe Illustrator

When you have stretches and orientations for a population of features, you might have a strain ellipse.  Why plot it by hand when you can let Adobe Illustrator do it for you?

Illustrator CS5's Line tool allows you to specify an angle and a length (stretch, in this case).  The line tool uses a slightly different system of orientation than in geology.  360/0 is east, 90 is north, 180 is west, and 270 is south.  So you must keep that in mind when plotting geologic orientations.

First, setup two guides that have an intersection at a convenient location on the artboard; lock your guides.  Use the line tool and snap-click on that intersection.  Define your angle (keeping in mind differences in orientation), and length (stretch).  Do this over and over at the same intersection point until you have exhausted your supply of data.

At this point you may need to copy sets of stretch lines, group them, duplicate, and horizontally or vertically reflect them to get a complete ellipse.  Ensure that their origins snap to your intersection of guides.

Now, use the Ellipse tool and setup a unit circle with radius  S=1 and snap the center of that circle to the intersected guide.  Duplicate the circle and use the shear tool to fit your data; use the scale tool if area cannot be preserved.  If all goes well, you'll end up with Lines of No Finite Extension at the intersection of the unit circle and your ellipse.  Snap drag lines to each intersection to define your fields of lengthening and shortening.

You can then use the incredibly handy Shape builder tool and text tools to clean up your ellipse for others to view.

Remember, to preserve the angular relationships of your resultant strain ellipse when scaling, use the same scaling factor for the horizontal and vertical.  It is really useful to scale so that you can draw (by hand) reasonable tangent lines to your ellipse to find ψ at any geologic orientation.  You could measure this in Illustrator, but I think that it would not be very efficient.