More progress... but more things I need to calculate that I don't yet know how.

README.md

@@ -2,4 +2,38 @@
 
 Functions to compute relative humidity, absolute humidity, wet bulb 
 temperature, and other values related to humidity of air, given 
-partial data
+partial data.
+
+## General architecture
+
+### The packet
+
+The 'packet', in the terminology of this library, is a map which has bindings
+for some of the following keywords:
+
+1. `:actual-humidity`
+2. `:actual-vapour-pressure
+1. `:dew-point`
+2. `:pressure-pascals` 
+3. `:pressure-millibars` 
+4. `:saturation-pressure`
+5. `:relative-humidity`
+6. `:temperature`
+7. `:temperature-celsius` 
+8. `:temperature-kelvin` 
+
+These keywords represent variables in the pressure equations, and they are all
+to a degree inter-related; so if you have (or can assume) some of them, you can
+compute others.
+
+Rather than having a mess of functions all of which call one another, which 
+seemed likely to result in horrible messes and potential infinite recursion,
+there is one central function, `humidity.core/resolution`, which takes a 
+partial package and repeatedly tries to compute the values for more variables
+until it can compute no more, and then returns the enhanced packet.
+
+At present there are no checks to ensure that the packet makes sense.
+
+Associated with each variable there is a namespace which takes a packet, and,
+if that packet contains enough information to compute that variable, returns
+a numeric value, else `nil`.

src/humidity/absolute.clj

@@ -33,6 +33,6 @@
 
 (defn abs-humidity [& {:keys [relative-humidity saturation-pressure temperature-kelvin]}]
   (when (and relative-humidity saturation-pressure temperature-kelvin)
-    (/ (* relative-humidity saturation-pressure) (* Rw temperature-kelvin 100)))
+    ;; I don't know why I'm having to multiply by a thousand here...
+    (* (/ (* relative-humidity saturation-pressure) Rw temperature-kelvin) 1000))
   )
-

src/humidity/constants.clj

@@ -9,9 +9,15 @@
   "Base of natural logarithms"
   2.71828)
 
+(def ^:const Pa
+  "Standard atmospheric pressure, in Pascals. I don't know why this isn't
+  100,000, but it isn't.
+  See https://en.wikipedia.org/wiki/Standard_atmosphere_(unit)"
+  101325)
+
 (def ^:const Pc
-  "Critical pressure for water, in MPa (Megapascal)"
+  "Critical pressure for water, in Pascals"
-  22.064)
+  22064)
 
 (def ^:const Rw
   "Specific gas constant for water vapour (J/(kg⋅K))"

src/humidity/core.clj

@@ -1,6 +1,6 @@
 (ns humidity.core
   (:require [humidity.absolute :refer [abs-humidity]]
-            [humidity.constants :refer [celsius-offset]]
+            [humidity.constants :refer [celsius-offset Pa]]
             [humidity.saturation-vp :as saturation-vp]
             [humidity.utils :refer [?assoc]]
             [humidity.wet-bulb :refer [wet-bulb-temperature]]))
@@ -8,7 +8,7 @@
 (defn resolve-humidity
   "Resolve humidity equations given the data in this packet."
   [& {:keys [temperature temperature-celsius temperature-kelvin relative-humidity
-             pressure-kilopascals pressure-millibars saturation-pressure] :as packet}]
+             pressure-pascals pressure-millibars saturation-vapour-pressure] :as packet}]
   (println packet)
   (if temperature (resolve-humidity (assoc (dissoc packet :temperature) :temperature-celsius temperature))
       (?assoc packet
@@ -22,13 +22,13 @@
                                      (and temperature-celsius relative-humidity)
                                       (wet-bulb-temperature temperature-celsius relative-humidity))
               :absolute-humidity (abs-humidity :relative-humidity relative-humidity
-                :saturation-pressure saturation-pressure
+                :saturation-vapour-pressure saturation-vapour-pressure
                 :temperature-kelvin temperature-kelvin)
-              :pressure-kilopascals (when-not pressure-kilopascals
+              :pressure-pascals (when-not pressure-pascals
-                                      (if pressure-millibars (/ pressure-millibars 10) 100))
+                                      (if pressure-millibars (* pressure-millibars 100) Pa))
               :pressure-millibars (when-not pressure-millibars
-                                    (if pressure-kilopascals (* pressure-kilopascals 10) 1000))
+                                    (if pressure-pascals (/ pressure-pascals 100) (/ Pa 100)))
-              :saturation-pressure (saturation-vp/saturation-vp packet))))
+              :saturation-vapour-pressure (saturation-vp/saturation-vp packet))))
 
 
 (defn resolution

src/humidity/relative.clj

@@ -1 +1,34 @@
-(ns humidity.relative)
+(ns ^{:authority "https://journals.ametsoc.org/view/journals/apme/35/4/1520-0450_1996_035_0601_imfaos_2_0_co_2.xml/"
+      :author "simon"
+      :doc "Function to return relative humidity."} humidity.relative
+  (:require [humidity.constants :refer [celsius-offset e]]
+            [humidity.utils :refer [expt]]))
+
+(def ^:const magic-numbers
+  "The magic numbers (empirical constants) from the derived expression. It
+   bothers me that all these formulae depend on 'empirical constants', *and*
+   that there is no commonality between the empirical constants of different
+   formulae."
+  [0 17.625 243.04])
+
+(def C magic-numbers)
+
+(defn rel-humidity
+  "Returns relative humidity (as a percentage, 0...100) given values for dew
+   point and temperature in either Celsius or Kelvin."
+  [& {:keys [dew-point temperature-celsius temperature-kelvin]}]
+  (cond (and dew-point (or temperature-celsius temperature-kelvin))
+    (let [Tc (if temperature-celsius
+               temperature-celsius
+               (- temperature-kelvin celsius-offset))]
+      (* 100 (/ (expt e (/ (* (C 1) dew-point)
+                           (+ (C 2) dew-point)))
+                (expt e (/ (* (C 1) Tc)
+                           (+ (C 2) Tc))))))))
+
+;; Absolute Humidity (grams/m3) = 6.112 × e^[(17.67 × T)/(T+243.5)] × rh × 2.1674
+;;                                -----------------------------------------------
+;;                                                   (273.15+T)
+;;
+;; => /
+;;

src/humidity/saturation_vp.clj

@@ -5,14 +5,16 @@
   (:require [clojure.math :refer [pow]]
             [humidity.constants :refer [celsius-offset e]]))
 
-
 (defn saturation-vp-tetens
-  "Calculate and return saturation vapour pressure in hPa using Tetens' 
+  "Calculate and return saturation vapour pressure in Pa using Tetens'
    formula, given temerature in ° Celsius."
   [temperature-celsius]
-  (let [a 6.1078 ;; yet more magic numbers...
+  (let [a 610.78 ;; yet more magic numbers...
+                 ;; NOTE: 610.78 rather than 0.61078 in source because
+                 ;; we want answer in Pascals.
         b 17.27
         c 237.3]
+  ;; constant 100 to convert to Pascals
     (* a (pow e (/ (* b temperature-celsius) (+ c temperature-celsius))))))
 
 (defn saturation-vp

src/humidity/wet_bulb.clj

@@ -1,5 +1,6 @@
 (ns ^{:doc "Function to calculate wet bulb temperature (in ° C) given temperature in
-   ° C and relative-humidity percentage (0...100)"} 
+   ° C and relative-humidity percentage (0...100)"
+   :author "simon"}
   humidity.wet-bulb
   (:require [clojure.math :refer [atan]]
             [humidity.utils :refer [expt]]))

test/humidity/absolute_test.clj

@@ -0,0 +1,13 @@
+(ns humidity.absolute-test
+  (:require [clojure.test :refer [deftest is testing]]
+            [humidity.constants :refer [celsius-offset]]
+            [humidity.absolute :refer [abs-humidity]]))
+
+(deftest absolute-humidity-test
+  (testing "definitional"
+    (let [min-expected 39.58
+          max-expected 39.59
+          actual (abs-humidity :relative-humidity 100
+                               :saturation-pressure 56.29
+                               :temperature-kelvin (+ 35 celsius-offset))]
+      (is (< min-expected actual max-expected)))))

test/humidity/dew_point_test.clj

@@ -0,0 +1 @@
+(ns humidity.dew-point-test)

test/humidity/relative_test.clj

@@ -0,0 +1,11 @@
+(ns humidity.relative-test
+  (:require [clojure.test :refer [deftest is testing]]
+            [humidity.constants :refer [celsius-offset]]
+            [humidity.relative :refer [rel-humidity]]))
+
+(deftest relative-humidity-test
+  (testing "Online examples"
+    (let [min-expected 99
+      max-expected 101
+      actual (rel-humidity :dew-point 35 :temperature-celsius 35)]
+    (is (< min-expected actual max-expected)))))

test/humidity/saturation_vp_test.clj

@@ -0,0 +1,10 @@
+(ns humidity.saturation-vp-test(:require [clojure.test :refer [deftest is testing]]
+  [humidity.constants :refer [celsius-offset]]
+          [humidity.saturation-vp :refer [saturation-vp saturation-vp-tetens]]))
+
+(deftest saturation-vp-test
+  (testing "from online sources"
+    (let [min-expected 5622
+      max-expected 5629
+      actual (saturation-vp {:temperature-celsius 35})]
+    (is (< min-expected actual max-expected)))))