Release 0.1.0

This is the initial release of the Predict library for crystal using the sgp4
model.

Author: RX14

.gitignore

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+/doc/
+/libs/
+/lib/
+/.crystal/
+/.shards/
+
+# Libraries don't need dependency lock
+# Dependencies will be locked in application that uses them
+/shard.lock
+
+### C++ ###
+# Prerequisites
+*.d
+
+# Compiled Object files
+*.slo
+*.lo
+*.o
+*.obj
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Compiled Dynamic libraries
+*.so
+*.dylib
+*.dll
+
+# Fortran module files
+*.mod
+*.smod
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+*.lib
+
+# Executables
+*.exe
+*.out
+*.app
+
+/src/predict/ext/test
+/bench

.travis.yml

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+language: crystal

LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2016 RX14
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+# predict.cr
+
+Predict is a satellite prediction library for crystal using the sgp4 model.
+The model used is the updated combined sgp/sdp4 model from the celestrak website.
+
+Predict can track the latitude, longitude and altitude of satellites, and also calculate look angles (azimuth, elevation, range) from an observer on the earth's surface.
+
+## Installation
+
+Add this to your application's `shard.yml`:
+
+```yaml
+dependencies:
+  predict:
+    github: RX14/predict.cr
+    version: 0.1.0
+```
+
+## Usage
+
+```crystal
+require "predict"
+
+# All values truncated to 4 decimal places for readability
+
+# Parse TLE
+tle = Predict::TLE.parse_three_line <<-TLE
+  ISS (ZARYA)
+  1 25544U 98067A   16339.72355294  .00003337  00000-0  58323-4 0  9990
+  2 25544  51.6456 287.6667 0006011 291.2532 140.8410 15.53794284 31519
+  TLE
+  
+# Inspect TLE data
+tle.name # => "ISS (ZARYA)"
+tle.catalog_number # => 25544
+tle.mean_motion # => 15.5379
+
+# Create satellite from TLE, this initialises the orbital model
+satellite = Predict::Satellite.new(tle)
+
+# Create a prediction from the TLE
+time = Time.new(2016, 12, 5, 12, 0, 0)
+satellite_position, satellite_velocity = satellite.predict(time)
+
+satellite_position # => Predict::TEME(@x=3815.7998, @y=1932.0874, @z=5261.6006)
+
+# Predict ground track
+satellite_position.to_lat_long_alt(time) # => Predict::LatLongAlt(@latitude=0.8913, @longitude=2.3062, @altitude=415.4529)
+
+# Predict look angles from an observer (200m altitude)
+observer = Predict::LatLongAlt.from_degrees(52.9, -2.24, 200.0)
+observer.look_at(satellite_position, time) # => Predict::LookAngle(@azimuth=0.50118495648349193, @elevation=-0.55812612380797122, @range=7501.0178628601843)
+```
+
+## Development
+
+SGP4 is bound as a static library in src/predict/ext. Use `make` with the optional make variables `release=true` or `debug=true` to build the static library. Make sure you run the specs and formatter before sending PRs.
+
+Useful reading material on sgp4 and coordinate systems is http://celestrak.com/columns/.
+
+## Contributing
+
+1. Fork it ( https://github.com/RX14/predict.cr/fork )
+2. Create your feature branch (`git checkout -b feature/foo`)
+3. Commit your changes (`git commit`)
+4. Push to the branch (`git push origin feature/foo`)
+5. Create a new Pull Request
+
+## Contributors
+
+- [RX14](https://github.com/RX14) - creator, maintainer, confused guy

bench.cr

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+require "./src/predict"
+require "benchmark"
+
+private def tle_name_zero
+  <<-TLE
+  0 AO-51 [+]
+  1 28375U 04025K   09105.66391970  .00000003  00000-0  13761-4 0  3643
+  2 28375 098.0551 118.9086 0084159 315.8041 043.6444 14.40638450251959
+  TLE
+end
+
+Benchmark.ips do |b|
+  b.report("tle") { Predict::TLE.parse_three_line(tle_name_zero) }
+end

shard.yml

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+name: predict
+version: 0.1.0
+
+authors:
+  - RX14 <[email protected]>
+
+scripts:
+  postinstall: make release=true -C src/predict/ext
+
+license: MIT

spec/predict/coordinates_spec.cr

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+require "../spec_helper"
+
+private def gmst(time)
+  Predict.greenwich_sidereal_time(time)
+end
+
+describe Predict do
+  describe ".greenwich_sidereal_time" do
+    it "calculates the correct GMST" do
+      gmst(Time.new(1995, 10, 1, 9, 0, 0)).should eq(2.5242182677688412)
+      # From IAU sofa tests
+      gmst(2400000.5 + 53736.0).should be_close(1.754174981860675096, 1e-12)
+    end
+  end
+
+  describe "TEME" do
+    describe "#to_lat_long_alt" do
+      it "converts TEME to lat/long/alt" do
+        teme = Predict::TEME.new(-4400.594, 1932.870, 4760.712)
+        expected = teme.to_lat_long_alt(Time.new(1995, 11, 18, 12, 46, 0))
+
+        expected.latitude.should be_close(44.91 * Predict::DEG2RAD, 0.5e-2)
+        expected.longitude.should be_close(-92.31 * Predict::DEG2RAD, 0.5e-2)
+        expected.altitude.should be_close(397.507, 0.5e-3)
+      end
+
+      it "round trips" do
+        time = Time.new(1995, 11, 18, 12, 46, 0)
+        expected = Predict::TEME.new(-4400.594, 1932.870, 4760.712)
+        actual = expected.to_lat_long_alt(time).to_teme(time)
+
+        actual.x.should be_close(expected.x, 1e-10)
+        actual.y.should be_close(expected.y, 1e-10)
+        actual.z.should be_close(expected.z, 1e-10)
+      end
+
+      it "round trips (random)" do
+        time = random_time
+        expected = random_teme
+        actual = expected.to_lat_long_alt(time).to_teme(time)
+
+        actual.x.should be_close(expected.x, 1e-10)
+        actual.y.should be_close(expected.y, 1e-10)
+        actual.z.should be_close(expected.z, 1e-10)
+      end
+    end
+  end
+
+  describe "LatLongAlt" do
+    describe "#to_teme" do
+      it "converts latitude/longitude/altitude to TEME" do
+        pos = Predict::LatLongAlt.from_degrees(40.0, -75.0, 0.0)
+        teme = pos.to_teme(Time.new(1995, 10, 1, 9, 0, 0))
+
+        teme.x.should be_close(1703.295, 0.5e-3)
+        teme.y.should be_close(4586.650, 0.5e-3)
+        teme.z.should be_close(4077.984, 0.5e-3)
+      end
+
+      it "round trips" do
+        time = Time.new(1995, 10, 1, 9, 0, 0)
+        expected = Predict::LatLongAlt.from_degrees(40.0, -75.0, 0.0)
+        actual = expected.to_teme(time).to_lat_long_alt(time)
+
+        actual.latitude.should be_close(expected.latitude, 1e-10)
+        actual.longitude.should be_close(expected.longitude, 1e-10)
+        actual.altitude.should be_close(expected.altitude, 1e-10)
+      end
+
+      it "round trips (random)" do
+        time = random_time
+        expected = random_lla
+        actual = expected.to_teme(time).to_lat_long_alt(time)
+
+        actual.latitude.should be_close(expected.latitude, 1e-10)
+        actual.longitude.should be_close(expected.longitude, 1e-10)
+        actual.altitude.should be_close(expected.altitude, 1e-10)
+      end
+    end
+
+    describe "#look_at" do
+      # it "finds look angles to a satellite" do
+      #   time = Time.new(1995, 11, 18, 12, 46, 0)
+      #   satellite = Predict::TEME.new(-4400.594, 1932.870, 4760.712)
+      #   observer = Predict::LatLongAlt.new(45.0, -93.0, 0.0)
+
+      #   look_angle = observer.look_at(satellite, time)
+
+      #   look_angle.azimuth.should be_close(100.36 * Predict::DEG2RAD, 0.5e-2)
+      #   look_angle.elevation.should be_close(81.52 * Predict::DEG2RAD, 0.5e-2)
+      #   look_angle.range.should be_close(81.52 * Predict::DEG2RAD, 0.5e-2)
+      # end
+    end
+  end
+end