sat, 05-mar-2011, 17:08

Nika, overflow

Nika, Goldstream Creek

The last couple days have seen a lot of overflow on Goldstream Creek, causing it to rise more than two feet. The water moved fast enough and it's been cold enough at night that it froze into a pretty good surface for ice skating. Many years ago we lived in a cabin at the edge of a pond near the railroad tracks and we bought ice skates so we skate on the pond. Turns out the number of days where the pond is frozen and not completely covered by snow is virtually zero, so we rarely got a chance to use them. But here, it seems that at least once or twice a year the overflow on the Creek or the DNR pond east of us will run over the snow and freeze into reasonably smooth ice.

I attempted to shoot a video while ice skating on the Creek today. It's not the greatest video, but it does give you some idea of what it looks like. After it freezes and before the overflow starts later in the winter, I spend a lot of time walking Nika and Piper down here. During breakup, the water rises to just below the bottom of the bridge, and then recedes to between four and five feet lower than where I'm skating by the middle of summer. The bridge I duck under is where I do my river stage measurements for the National Weather Service.

tue, 01-mar-2011, 18:47

Sunset, Miller Hill

Sunset, Miller Hill

People always ask if we’re the coldest spot in town. I can’t really answer that, but I can find out if we’re the coldest reporting weather station in the region.

Once again, we’ll use PostgreSQL window functions to investigate. The following query finds the station in zone 222 (the National Weather Service region that includes Fairbanks) reporting the coldest temperature every hour during the winter, counts up all the stations that “won,” and then ranks them. The outermost query gets the total number of hourly winners and uses this to calculate the percentage of hours that each station was the coldest reporting station.

Check it out:

SELECT station, count,
    round(count / sum(count) OVER (
    ) * 100, 1) AS percent
    SELECT station, count(*) AS count
    FROM (
        SELECT station, dt_local, temp_f,
            rank() OVER (
                PARTITION BY dt_local ORDER BY temp_f
        FROM (
            SELECT location || ' (' || station_id || ')' AS station,
                date_trunc('HOUR', dt_local) AS dt_local, temp_f
            FROM observations
                INNER JOIN stations USING (station_id)
            WHERE zone_id = 222
                AND dt_local between '2010-10-01' and '2011-03-31'
        ) AS foo
    ) AS bar WHERE bar.rank = 1 GROUP BY station ORDER BY count desc
) AS foobar;

And the results:

                station                 | count | percent
 Goldstream Creek (DW1454)              |  2156 |    51.0
 Chena Hot Springs (CNRA2)              |   484 |    11.5
 Eielson Air Force Base (PAEI)          |   463 |    11.0
 Parks Highway, MP 325.4 (NHPA2)        |   282 |     6.7
 Small Arms Range (SRGA2)               |   173 |     4.1
 Ballaine Road (AS115)                  |   153 |     3.6
 Fairbanks Airport (PAFA)               |   125 |     3.0
 Fort Wainwright (PAFB)                 |   107 |     2.5
 Ester Dome (FBSA2)                     |   103 |     2.4
 Eagle Ridge Road (C6333)               |    81 |     1.9
 Keystone Ridge (C5281)                 |    33 |     0.8
 Skyflight Ave (D6992)                  |    21 |     0.5
 14 Mile Chena Hot Springs Road (AP823) |    21 |     0.5
 College Observatory (FAOA2)            |    11 |     0.3
 Geophysical Institute (CRC)            |    10 |     0.2
 DGGS College Road (C6400)              |     1 |     0.0

Answer: Yep. We’re the coldest.

Update: Thinking about this a little bit more, the above analysis is biased against stations that don't report every hour. Another way to look at this is to calculate the hourly average temperature, subtract this from the data for each station during that hour, and then average those results for the whole winter. The query is made more complex because several stations report temperatures more than once an hour. If we simply averaged all these observations together with the stations that only reported once, these stations would bias the resulting hourly average. So we average each station's hourly data, then use that to calculate the zone average for the hour. Here's the query, and the results:

SELECT station, 
    round(avg(diff), 1) AS avg_diff 
    SELECT station,
        temp_f - avg(temp_f) 
            OVER (
                PARTITION BY dt_local 
            ) AS diff 
    FROM (
        SELECT location || ' (' || station_id || ')' AS station, 
            date_trunc('HOUR', dt_local) AS dt_local, 
            avg(temp_f) AS temp_f 
        FROM observations 
            INNER JOIN stations USING (station_id) 
        WHERE zone_id = 222 AND 
            dt_local between '2010-10-01' and '2011-03-31' 
        GROUP BY station, date_trunc('HOUR', dt_local)
    ) AS foo
) AS bar 
GROUP BY station 
ORDER BY avg_diff;
                station                 | avg_diff
 Goldstream Creek (DW1454)              |     -6.8
 Eielson Air Force Base (PAEI)          |     -3.8
 Fort Wainwright (PAFB)                 |     -3.1
 Fairbanks Airport (PAFA)               |     -2.9
 Small Arms Range (SRGA2)               |     -2.8
 Chena Hot Springs (CNRA2)              |     -2.3
 DGGS College Road (C6400)              |     -0.7
 Ballaine Road (AS115)                  |     -0.6
 College Observatory (FAOA2)            |      1.0
 North Bias Drive (RSQA2)               |      1.3
 14 Mile Chena Hot Springs Road (AP823) |      3.1
 Skyflight Ave (D6992)                  |      3.3
 Geophysical Institute (CRC)            |      3.5
 Eagle Ridge Road (C6333)               |      3.8
 Parks Highway, MP 325.4 (NHPA2)        |      4.5
 Keystone Ridge (C5281)                 |      5.1
 Ester Dome (FBSA2)                     |      5.1
 Birch Hill Recreation Area (BHS)       |      6.8
sun, 30-jan-2011, 09:52

Location map

Location map

A couple years ago we got iPhones, and one of my favorite apps is the RunKeeper app, which tracks your outdoor activities using the phone’s built-in GPS. When I first started using it I compared the results of the tracks from the phone to a Garmin eTrex, and they were so close that I’ve given up carrying the Garmin. The fact that the phone is always with me, makes keeping track of all my walks with Nika, and trips to work on my bicycle or skis pretty easy. Just like having a camera with you all the time means you capture a lot more images of daily life, having a GPS with you means you have the opportunity to keep much better track of where you go.

RunKeeper records locations on your phone and transfers the data to the RunKeeper web site when you get home (or during your trip if you’ve got a good enough cell signal). Once on the web site, you can look at the tracks on a Google map, and RunKeeper generates all kinds of statistics on your travels. You can also download the data as GPX files, which is what I’m working with here.

The GPX files are processed by a Python script that inserts each point into a spatially-enabled PostgreSQL database (PostGIS), and ties it to a track.

Summary views allow me to generate statistics like this, a summary of all my travels in 2010:


Another cool thing I can do is use R to generate a map showing where I’ve spent the most time. That’s what’s shown in the image on the right. If you’re familiar at all with the west side of the Goldstream Valley, you’ll be able to identify the roads, Creek, and trails I’ve been on in the last two years. The scale bar is the number of GPS coordinates fell within that grid, and you can get a sense of where I’ve travelled most. I’m just starting to learn what R can do with spatial data, so this is a pretty crude “analysis,” but here’s how I did it (in R):

drv <- dbDriver("PostgreSQL")
con <- dbConnect(drv, dbname="new_gps", host="nsyn")
points <- dbGetQuery(con,
    "SELECT type,
        ST_X(ST_Transform(the_geom, 32606)) AS x,
        ST_Y(ST_Transform(the_geom, 32606)) AS y
     FROM points
        INNER JOIN tracks USING (track_id)
        INNER JOIN types USING (type_id)
     WHERE ST_Y(the_geom) > 60 AND ST_X(the_geom) > -148;"
points_ppp <- ppp(points$x, points$y, c(min(points$x), max(points$x)), c(min(points$y), max(points$y)))
Lab.palette <- colorRampPalette(c("blue", "magenta", "red", "yellow", "white"), bias=2, space="Lab")
spatstat.options(npixel = c(500, 500))
map <- pixellate(points_ppp)
png("loc_map.png", width = 700, height = 600)
image(map, col = Lab.palette(256), main = "Gridded location counts")

Here’s a similar map showing just my walks with Nika and Piper:

Hiking trips

Walks with Nika and Piper

And here's something similar using ggplot2:

m <- ggplot(data = points, aes(x = x, y = y)) + stat_density2d(geom = "tile", aes(fill = ..density..), contour = FALSE)
m + scale_fill_gradient2(low = "white", mid = "blue", high = "red", midpoint = 5e-07)

I trimmed off the legend and axis labels:

ggplot2 density map

ggplot2, geom_density2d

tags: GPS  gpx  iPhone  R  statistics 
sat, 29-jan-2011, 21:53

Deuce, On Chesil Beach

Deuce, On Chesil Beach

I’ve read a lot of Ian McEwan over the years, and it’s impressive how different his stories are, and how precise and well written they are. On Chesil Beach is a horror of a story where a single moment is fully visualized and expertly drawn, and when it, ahem, comes, you know that things will never be the same for the characters. I guess this is McEwan’s expertise: visualizing characters suddenly drawn into situations so far from their expectation that you never quite know how they will react.

In this case, one wonders if the outcome of the story would be different if the time or place were different? I should hope that a more modern sensibility, more open dialog about intimacy, perhaps even premarital sexual investigation, would prevent the sort of misunderstanding that’s at the center of this book.

Anyway, I enjoyed it, but I wasn’t as blown away as many of the reviewers were. I do like, oddly enough, what People magazine wrote about the book:

No one can unpack a single frozen moment better than McEwan.

Very true.

tags: books  Deuce 
sat, 29-jan-2011, 17:47

Genesee Beer

Genesee Beer

Most Fridays we get take out from our local Thai restaurant, Lemongrass, and sometimes we stop at a convenience store on the way to see if there are any interesting or new beers (and sometimes wine) available. Yesterday I saw one of these, a 24-ounce can of Genesee Beer. A couple years ago I found a six-pack of Genesee Cream Ale at Goldhill Liquor, but I haven’t seen straight-up Genesee since I left Rochester a couple decades ago. Needless to say, I bought it, and am now very much enjoying the refreshing, light taste, with just a bit more than a hint of corn in the flavor.

My favorite homebrew, Piper’s Irish-American Red Ale also has this subtle corn flavor. Corn (and later, rice) have a distinct place in American brewing history because it was a way to reduce the excess protein found in the 6-row barley that grew well in North America. By contrast, the traditional European brewing grain, 2-row barley, only has enough enzymes (protein) to convert it’s own starches to sugars, so there wasn’t a problem with excess protein in the final beer. With 6-row grain, there are enough enzymes to convert additional brewing adjuncts like corn, reducing the protein content in the final beer (and also, incidentally, making the beer cheaper to produce).

Genesee Brewing has been in continuous operation (except for during Prohibition, of course) in Rochester, New York since 1878, and is still an independently owned brewery that’s part of the North American Breweries name (along with Labatts, Pyramid, MacTarnahan’s and a few other small breweries). If you’re going to drink an American light lager, it might as well be a good one like Genesee instead of the mega-industry, foreign-owned, over-commercialized swill like Budweiser, Coors, Miller, etc.

tags: beer  Genesee  Rochester 

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