Sunday Sep 20, 2009 at 13:57
TPE updated to 1.0 RC1
I’ve updated TPE today to version 1.0 RC1 – it’s close to done (for version 1 at least).
A couple of features of note:
Elevation
I’ve been using the SRTM (Shuttle Radar Topography Mission) data set via the Geonames web service. This is a fairly mature data model and the quality is high. However, it has a couple of limitations for our purposes.
Firstly, the latitudes of the model extend only to 60° north and 56° south – not far enough for some of the locations that photographers get to nowadays.
Secondly, many mountainous peaks and slopes would return “No Data” due to measurement difficulties when the angle of incidence of the radar was too high. Again, many landscape photographers are interested in precisely these locations.
In this version we’re adding two other elevation data models to the mix: ASTER GDEM and GTOPO30.
ASTER GDEM was released only earlier this summer, but Geonames already has a web service supporting it. The coverage is much wider (83° north and 60° south) and mountainous areas are better covered.
However, there are apparently still some holes and data anomolies in the model (see the reference in the Wikipedia article linked above).
GTOPO30 is another model with even wider coverage but with lower resolution and the data is older than the other two sources.
So, in the new version of TPE, I query SRTM first and then ASTER and finally GTOPO30 if either preceding service returns “no data” (or the location is out of range).
Twilight azimuths
I had a request from Tim Parkin to display the azimuth lines for the sun both before sunrise and after sunset. This is useful if you’re looking to track the twilight glow on the horizon.
So, the program now shows this (in the Details View) up until the end (or from the start) of Astronomical Twilight.
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Stephen · Sunday, September 20, 2009, 13:57 · Permalink
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19:41 22 Sep 2009
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03:23 21 Sep 2009