Wednesday, January 14, 2015

Support CalTopo: GPS Maps

There are still some environments where a smartphone won't do, and you need the battery life and weather resistance of a dedicated GPS.  SAR is one of those environments, but it's also one that demands accurate, high-quality maps.  Once you've gotten used to tracking your location on a satellite image, or dodging cliffs on a steep descent using slope angle shading, it's hard to go back to a confusing mess of blocky contour lines rendered in 160x240 resolution.

Enter custom GPS maps from CalTopo, available with large-area coverage on 32GB MicroSD cards.  Preload the same high-quality maps that power caltopo.com onto your GPS and never worry about having to download imagery or deal with inadequate maps again.  Before I get too deep into the cheerleading, bad news first.

Garmin doesn't want to just sell you a GPS, they want to sell you a pure-gravy BirdsEye subscription as well.  The only way that works is if they're the only game in town when it comes to GPS imagery, which they accomplish by "locking" their units to only work with official Garmin maps.  In order to use CalTopo's custom GPS maps, you need to unlock your GPS as described here.  I'd be willing to pay a licensing fee to Garmin in order to get my maps officially sanctioned, since that would allow me to sell trouble-free cards through major retailers, but I've asked and they're not interested.

So on to the good news.  You live in California, Oregon or Washington and are in the market for some maps that will work with a newer Garmin GPS that you have unlocked.  As an added bonus, you'd like those maps to match your printed CalTopo maps 1:1.  You're in luck!  The following are real screenshots taken from my 62s.

 

Yosemite Valley, Rodeo Beach and Mt Shasta.

The three layers available are:

  • Scanned USGS Topo Maps, to an equivalent zoom of 15.
  • 2 meter per pixel aerial imagery, to an equivalent zoom of 16.  NAIP Aerial layer used for California, US Topo Imagery layer used elsewhere.
  • Slope angle shading with Forest Service maps replacing USGS topos where available. 
Some additional screenshots, of Mt Rainier and the San Juan Islands:




Check out the CalTopo Store today!

Monday, January 12, 2015

Elevation and Vegetation at a Glance

Long distance hiking leaves plenty of time for reflection, and an accelerated JMT trip I did this fall was no exception.  Despite being armed with maps and elevation profiles, I realized that I still wasn't aware whether a given day would be spent in shady forests or on barren, south-facing slopes.  I'd also been pondering a better way to size up search areas for SAR, and decided to solve both those problems with a new stats dialog.  It took a couple months to put the idea into production, but it's finally here.

Like with elevation profiles, there are two ways to bring up a stats dialog.  One is to right click on a line or polygon, and choose Stats.  The second is to right-click on the map background, choose Measure, and then either Line Stats or Area Stats.


Either option will probably involve a short delay as CalTopo pulls up the relevant elevation and vegetation data, followed by a dialog.  Unlike with elevation profiles, polygons will bring up data for the polygon's interior rather than just its perimeter.


The first two charts are elevation and slope histograms, along with min, max and average values; color-coding on the slope histogram matches CalTopo's slope shading layers.  The third chart is a circular histogram tracking aspect across 45 degree slices.  The pie slices are area-proportional rather than radius-proportional, i.e. if N aspects are 50% as frequent as W aspects, then the N pie slice will cover half the area of the W pie slice, with a radius that's 70% as large.


The tree cover histogram shows tree canopy coverage - 100% means that trees completely block all views of the sky.  Land cover shows land coverage as listed in the National Land Cover Dataset (NLCD).

In addition to other benefits, this provides another quick sanity check on planned routes for backcountry skiing.