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Full Discussion: XY interpolation by time in awk
Top Forums Shell Programming and Scripting XY interpolation by time in awk Post 302929056 by Joćo Noiva on Wednesday 17th of December 2014 08:37:34 AM
Old 12-17-2014
Dear Don,

First I want to thank you for you suggestion and correction of the equation that was obviously wrong as RudiC also said.

Secondly I also thank you for your clean, simple and functional code!

Thirdly I ask you if you don't my mind a little more help.

I have a second pack of data that I need to interpolate based on the previous interpolated file.

I try to be short and clear:

Based on the RESULT.txt file (with all the data interpolated) I need to interpolate the values from a second file AIS_557.txt that have (due to issues during data acquisition) very few data points and with time stamps without decimals, based on first file. See example:


Code:
RESULT.TXT
010001 0469557.90 4266045.60 1386557563.76
010002 0469558.32 4266046.88 1386557564.65
010003 0469558.65 4266048.13 1386557565.55
010004 0469558.94 4266049.05 1386557566.45
010005 0469559.24 4266049.98 1386557567.36
010006 0469559.53 4266050.89 1386557568.25
010007 0469559.82 4266051.82 1386557569.16
010008 0469560.48 4266053.00 1386557570.05
010009 0469561.10 4266054.12 1386557570.95
010010 0469561.64 4266055.28 1386557571.85
010011 0469562.00 4266056.50 1386557572.76
010012 0469562.25 4266057.80 1386557573.66
010013 0469562.52 4266059.11 1386557574.55
010014 0469562.88 4266060.08 1386557575.45
010015 0469563.23 4266061.05 1386557576.35
010016 0469563.59 4266062.03 1386557577.25
010017 0469563.95 4266063.01 1386557578.16
010018 0469564.31 4266063.98 1386557579.06
010019 0469564.85 4266065.22 1386557579.95
010020 0469565.34 4266066.47 1386557580.85
010021 0469565.79 4266067.67 1386557581.76
...........


Code:
 AIS_557.txt
468953.73 4264882.13 1386533790
468944.97 4264871.07 1386533820
468936.22 4264860.01 1386533850
468927.46 4264848.94 1386533880
468918.70 4264837.88 1386533910
468918.65 4264826.79 1386533940
468909.89 4264815.72 1386533970
468892.38 4264793.60 1386534030
468883.62 4264782.54 1386534060
468874.90 4264782.57 1386534090
468866.14 4264771.51 1386534150
468857.43 4264771.54 1386534180
468839.95 4264760.51 1386534210
468822.43 4264738.39 1386534240
468813.67 4264727.33 1386534270
..........

So I need to find the best fit for each time stamp of AIS file on the RESULT file. Interpolate X Y (for each time stamp of RESULT file) for the second file (AIS file).

Me and a colleague we are trying to adapt your function to do this but it is not working yet. The code is this one:

Code:
awk '
function interpola(i, P1, P2,  Xi, Yi) {
	Xi= Xais[P1] +((Xais[P2]-Xais[P1])*(Tsis[i]-Tais[P1]))/(Tais[P2]-Tais[P1])
	Yi= Yais[P1] +((Yais[P2]-Yais[P1])*(Tsis[i]-Tais[P1]))/(Tais[P2]-Tais[P1])
	printf("%06i %010.2f %010.2f %013.2f\n", FFID[i], Xi, Yi, T[i])
#	print FFID[i], T[i], P1, P2 #test fitting points for interpolation (keeps line number where are P1 or P2)
}
{
NR==FNR{Tsis[FNR]=$4; Sis[FNR]=$0; next} # Reads the first file with principal serie 
{Xais[FNR]=$1; Yais[FNR]=$2; Tais[FNR]=$3 } # Reads the second file with AIS values to interpolate

}
END {
for (i in Tsis[FNR]) {
	for (j=1; j<FNR; j++) {	# Runs down until find P1
		if (Tsis[i]>Tais[FNR]) {
			P1=j
			break
		}
	}
	for (k=j; k<=FNR; k++) { # Runs down until find P2
		if ((Tsis[i]<Tais[FNR]) ) {
			P2=k
			break
		}
	}	
	interpola(i, P1, P2) 	#interpolation and print interpolated values
}

}' '  RESULT.txt AIS_557.txt  > AIS_INTERPOLATION.txt

Can you give us, please, a suggestion!

Thanks in advance
 

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