fix: hw4 knit

hw4.Rmd

@@ -1,4 +1,15 @@
-# HW 4
+---
+title: "HW4"
+subtitle: "Software Defined Radio"
+output: pdf_document
+date: "`r Sys.Date()`"
+---
+
+```{r setup, include=FALSE}
+knitr::opts_chunk$set(echo = TRUE)
+```
+
+# Assignment
 Write an R script to calculate the output of the Klobuchar model.
 Provide a GUI means for entering input data, and the name and the
 path to navigation message file with coefficients of the Klobuchar
@@ -9,14 +20,20 @@ signal during 24 hours of a given day, in 1-minute increments, with
 the given coefficients of the ionospheric model. Verify the correctness
 of the algorithm implementation with a given numerical example. After
 that, conduct a 24-hour simulation of the GPS ionospheric delay in 1-
-minute increments for the position φu = 45.33709°, λu = 14.42496°, E
-= 90°, A = 180°. Store the estimated 24-hour simulation data set in a
+minute increments for the position $\varphi_u$ = 45.33709°, $\lambda_u$ = 14.42496°, $E$
+= 90°, $A$ = 180°. Store the estimated 24-hour simulation data set in a
 dedicated file on the local disc.
 
 The problem description, method, R script and implementation results
 should be presented in a single HTML document, which should be
 sent to the subject teacher's e-mail by May 21, 2026 at 23:59 CEST.
 
+# Input
+
+```{r select-file}
+library(rstudioapi)
+rinex_file <- rstudioapi::selectFile()
+```
 
 ```{r read-file}
 # Function to extract Klobuchar parameters from a RINEX navigation file
@@ -49,8 +66,43 @@ extract_klobuchar_parameters <- function(rinex_file) {
   )
 }
 
-rinex_file <- "brdc0930.26n"
 klobuchar_params <- extract_klobuchar_parameters(rinex_file)
 
 print(klobuchar_params)
+```
+
+```{r select-date}
+# TODO
+selected_date <- as.Date("2000-1-1")
+```
+
+# Klobuchar calculation
+1. Calculate earth-centered angle
+What are R_E and h?
+$$ \psi = \pi/2 - E - \arcsin(\frac{R_E}{R_E + h} \cos(E))  $$
+
+
+2. Compute the latitude of the IPP (ionospheric pierce point)
+$$ \phi_I = \arcsin( sin \varphi_u \cos \psi + \cos\varphi_u \sin\psi \cos A )$$
+3. Compute the longitude of the IPP
+$$ \lambda_I= \lambda_u + \frac{\psi \sin A}{\cos \phi_I}$$
+4. Find the geomagnetic latitude of the IPP
+What is phi_P?
+$$ \phi_m = \arcsin(\sin\phi_I \sin\phi_P + \cos\phi_I \cos\phi_P \cos(\lambda_I - \lambda_P)) $$
+5. Find the local time at the IPP
+$$ t = 43200 \lambda_I / \pi + t_{GPS} $$
+$\lambda_I$ in radians, $t$ in seconds.
+where $0 \leq t \leq 86 400$. Therefore:
+If $t \geq 86 400$, subtract $86 400$. If $t < 0$, add $86 400$.
+
+6. Compute the amplitude of ionospheric delay
+$$ A_I = \sum_{n=0}^{3} \alpha_n(\phi_m/\pi)^n $$
+If $A_I < 0$, then $A_I =0$.
+```{r simulate}
+# input constants
+lat = 45.33709 # phi
+lon = 14.42496 # lambda
+E = 90
+A = 180
+
 ```