Sunday, December 23, 2012

A Little GPS Sidekick

Recently I've begun to use the Bad Elf Pro GPS.  It looks like a digital stop watch and is operated in a similar fashion.  But that is where the similarities end.  The Bad Elf Pro is a fully-functional GPS with WAAS support and provides GPS information to supported Bluetooth devices.  For iOS devices, the device uses Core Location services, which allows it to override any on-board GPS device.

I have been testing the Bad Elf Pro in the field... kind of.  Its first major field trip was to the island of Maui, Hawaii, USA.  I used it to track the entire trip so that I could geotag my Canon G11 photographs using Aperture.  It worked great.  The Bad Elf went from sea level to 10,023 feet on Haleakala.  It tracked, at one second intervals, our every negotiated curve during the drive to Hana and all the way around.  The only time it might have failed was when I thought I had it on and data-logging (tracking) but that ended up not being the case.  Fortunately I was at a single location the entire time.  I have no idea what happened but I quite possibly was at fault.  In any case, geotagging my 600 photos worked flawlessly.

So the Bad Elf Pro proved to me that it is ready for a more rigorous field experience.  I have a WiFi iPad that does not have an on-board GPS.  When paired via Bluetooth with the Bad Elf, it can become a full-fledged mapping tool.  I can also use it with my iPhone and turn off all of its radios (except Bluetooth).  This is important because CDMA iPhones turn off the GPS receiver when the cellular radio is turned off... and when you're in the deep woods with high topographic relief, iPhones will kill themselves in hours.  During my visit to Haleakala and around the volcano, my iPhone had a very good battery life when using only Bluetooth.  The Bad Elf might be a match made in heaven with an inexpensive iPod Touch...

A few apps that look promising for field mapping on an iOS device:

  •  Avenza's PDF Maps -- compatible with ArcMaps geospatial PDF output, USGS PDF Topos, and USFS PDF Topos (thanks to Julie Donnelly-Nolan at USGS for the tip!)
  • Trimble's MyTopo Maps -- a quick way to get [mostly] seamless topos for all of the US on-the-fly... and offline (may need Elite account).  I did find a huge seam on the island of Maui.
The Bad Elf Pro looks to be a great GPS sidekick.

Monday, February 6, 2012

4 Gigabyte GeoTIFFs

I had a fight with Arc 9.3 today.  It refused to load a 4 GB GeoTIFF that was provided to me.  It was a 1.0 m DEM.   It didn't even bother to try reading the raster into memory.  It simply failed with a generic error message.  Arc 10 on a different workstation could load it, however.   Drat.  I had to install Arc 10 today on my own workstation.  Good thing I can choose to create Arc 9.3 geodatabases with the appropriate tool.

Interestingly, Arc 9.3 is fine with massive GRID or Imagine rasters.  Sort of.  Actually, on my workstation, you really shouldn't bother.

In this case I needed a slope map.  I also needed 20 ft contours.  I didn't want to split the raster into pieces.  Clearly, for this project, the answer was to resample the data to a larger cell size.  This speeds up geoprocessing exponentially.  Just be sure to do it reasonably.

Tomorrow I will map out geomorphic features of a 2 or 5 m DEM using slope class among other things.  I love my job.

Sunday, February 5, 2012

Basics of Geologic Mapping using ArcInfo Workstation and ArcDesktop 10

ArcInfo Workstation has inherent topology.  As a Geologist, you can use it to ensure appropriate spatial integrity between rock units, faults, and contacts.  ArcDesktop does not, by default, empower users in this way.  That explains why educated GIS users can become very frustrated with those with no concept of GIS (how many slivers, overlaps, and self-intersections caused by "dangerous" GIS users have you had to fix?).  One must go through a series of steps to duplicate what Workstation provides at the get-go.

Fortunately, through the use of geodatabases and a few Arc tools, users of Desktop can ensure topologically correct geologic maps.  You must define topology for lines, generate "labels" using points, and then create areas (rock units) from these parts using the Feature to Polygon tool (Arc 10 no longer provides an option to generate polygons within the right-click feature dataset context menu).  If you're particularly savvy, you can export lines, points, and areas into a coverage for Workstation.  Unfortunately, Workstation will no longer be supported after Arc 10.  So... old-school geologists will need to move on.

If in the future you need to update only a part of the spatial data, you can clip, update lines, erase, load, generate polygons, and update (I may go into more detail later).

QGIS has yet to provide a neat way to enforce rules of topology.  GRASS, however, can do it without any problems.  It's basically built in as with ArcInfo Workstation.  But good luck convincing organizations to use GRASS -- even if those organizations had helped to develop it!

This post is really meant to grease the wheels and convince me to begin posting regularly again.  Will it work?

Monday, June 13, 2011

Makes me smile when...

Makes me smile when TAs mention that my maps were the best in class.  Remote sensing was a fun course.  I learned a lot and would love to use those skills along with GIS (perhaps coupled with Python) to extract valuable information.  Here I go into the job market; I've graduated!

More useful posts to come!

Friday, June 3, 2011


I'm graduating very soon. Next week, I have finals.  This is why I have not posted anything recently.  I have lots of neat tricks to write about once I have the time.  Technology loves geology.

Wednesday, May 11, 2011

Topographic Profile From Basemap Contours, not a DEM

There are times when USGS DEMs do not match topography on basemaps.  I have a basemap that does not appear to be derived from any presently available USGS products.  DEMs are often interpolated from 7.5' quads, by using air photo stereopairs, SRTM, and so on.  The topography on the basemap I have is much more detailed than any DEM or USGS 7.5' topo I have come across.  So it was probably drafted by someone else.  Thus I set out to extract a topographic profile line using the basemap and Arc.  This is a pretty simple process, and it relies on geostatistics to interpolate elevation in between captured points.  The following instructions assumes you are familiar with principals of GIS.
  1. Plot your cross section line
  2. Capture elevation points on each contour that crosses your cross section line
    1. It is best to turn on edge-snapping if you're using Arc Desktop 10
    2. Make sure you capture the start and end points of your cross section line; you may have to interpolate elevation yourself.  In fact, there may times along the cross section line where it would make sense to estimate elevation, such as at bottoms of streams or tops of ridges.
  3. Krig your elevation points or use an interpolation method that you're comfortable with 
  4. Use Spatial Analyst or 3D Analyst (or open source equivalents) to generate a profile line along the resultant raster
  5. The more elevation points you capture, the better.
  6. Export the profile data to tabular format and use as desired (see blog post on Illustrator and profile lines)
  7. Rejoice in avoiding drafting a profile line by hand!
I ended up with very reasonable results in a much shorter time than by hand.  Now my topographic profile matches the basemap and it is is much more accomodating of the geology I mapped!  The lesson here is to compare USGS DEMs to your basemap before trusting DEM derived products.  Attention to detail is always key.

Sunday, April 24, 2011

Coloring Cross Sections: Adobe Illustrator Paint Groups

A while ago I posted a procedure on how to create a topographic cross section in Adobe Illutrator without vertical exaggeration ("Geologic Cross Sections and Adobe Illustrator").  The procedure used tabular elevation and distance data and Adobe Illustrator.  In that post, I did not explain what to do next.  So here's some more guidance.  Screen captures or a video may come later.
  1. Export your completed geologic map WITH the cross section line(s) from Arc or your chosen GIS to Illustrator-friendly format at 300 DPI.  
  2. Embed or link the AI geologic map file into your cross section Illustrator file.
  3. Rotate and align your newly imported map and a cross section line to the bottom of the profile's distance (X) axis (or at the bottom of the lowest elevation on your profile).  This is where you find out if your profile is at map scale!
  4. Create a new layer, call it "Cross Section Edges"
  5. Select the layer and project lines of appropriate weight (contact vs. fault) from the intersection of the X axis and the map's contacts or faults up through the profile line. 
  6. Begin drawing your beds using strike and dip information, remembering to use apparent dips when necessary.
  7. Be sure that all your lines end at another path.  For example, a contact line might end at the boundary of your profile chart or at a fault.  Do not leave gaps open between any paths.
  8. When you're done drawing all your bedding and faults, select all of your cross section art and turn it into a Live Paint Group
  9. Now Live Paint all the faces and edges!  See Adobe's help for more information.
  10. If you need to use patterns (say, from the FGDC Geologic Map Symbol website) and a unit color, I suggest coloring first, then copy the entire paint group, paste into place, and paint using a pattern.  Hopefully your patterns have transparent backgrounds.
  11. I also suggest creating new layers for every component of your cross section such as legend, title, and other information.
  12. Use the Lock layer tool and smart guides to your benefit!