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?