converting genomic coordinates to transcript coordinates

[amias]

Hello,
I need to convert the genomic coordinates for UTR and CDS features in the arabidopsis gff3 gene annotations to transcript coordinates. Can anyone suggest a way to do this using awk or other languages? I have tried to first calculate the length of the features for each ID, so that I can calculate the feature start and end positions for each transcript based on the length. However I am not sure how to write the code for the second part. I have searched for related threads but none of the solution seemed to provide what I want. Is there already a package or script for this kind of conversion? Any suggestion is most welcome!

Here is a sample of my input data:

more Athaliana_167_TAIR10.gene.gff3 
##gff-version 3
##annot-version TAIR10
Chr1    phytozomev10    gene    3631    5899    .       +       .       ID=AT1G01010.TAIR10;Name=AT1G01010
Chr1    phytozomev10    mRNA    3631    5899    .       +       .       ID=AT1G01010.1.TAIR10;Name=AT1G01010.1;pacid=19656964;longest=1;Parent=AT1G01010.TAIR10
Chr1    phytozomev10    five_prime_UTR  3631    3759    .       +       .       ID=AT1G01010.1.TAIR10.five_prime_UTR.1;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    CDS     3760    3913    .       +       0       ID=AT1G01010.1.TAIR10.CDS.1;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    CDS     3996    4276    .       +       2       ID=AT1G01010.1.TAIR10.CDS.2;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    CDS     4486    4605    .       +       0       ID=AT1G01010.1.TAIR10.CDS.3;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    CDS     4706    5095    .       +       0       ID=AT1G01010.1.TAIR10.CDS.4;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    CDS     5174    5326    .       +       0       ID=AT1G01010.1.TAIR10.CDS.5;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    CDS     5439    5630    .       +       0       ID=AT1G01010.1.TAIR10.CDS.6;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    three_prime_UTR 5631    5899    .       +       .       ID=AT1G01010.1.TAIR10.three_prime_UTR.1;Parent=AT1G01010.1.TAIR10;pacid=19656964
Chr1    phytozomev10    gene    5928    8737    .       -       .       ID=AT1G01020.TAIR10;Name=AT1G01020
Chr1    phytozomev10    mRNA    5928    8737    .       -       .       ID=AT1G01020.1.TAIR10;Name=AT1G01020.1;pacid=19655142;longest=1;Parent=AT1G01020.TAIR10
Chr1    phytozomev10    CDS     8571    8666    .       -       0       ID=AT1G01020.1.TAIR10.CDS.1;Parent=AT1G01020.1.TAIR10;pacid=19655142

Here is my working code based on the thread here for calculating the UTR and CDS feature length for each transcript:

awk '$3!="gene" && $3!="mRNA"' <Athaliana_167_TAIR10.gene.gff3|awk  '$9~/Parent/{sub(/.*Parent=/,"",$9);sub(/.TAIR10;.*/,"",$9);ID=$9;L[ID]=$5-$4+1}{for(i in L){print $0,L[i]}}'