Problem with samtools depth?

[twaddlac]

I'm trying to plot the depth of coverage but when running samtools depth it seems to skip over bases which I presume have no alignments spanning those regions. However, it does report some bases where there are no alignments, though few and it nowhere near compensates for the bases that it omits.

After grepping through the file the number of bases for the reference provided by samtools depth is always less then the actual number of bases. I made sure that there would be no character incompatibilities (Ns etc.) and still no improvement. Has anyone noticed this before? Is this a bug or does it just not display positions with no alignments?

I'm using samtools version 0.1.18 (r982:295) and produced bam files from both SHRiMP and Bowtie.

[Richard Finney]

The samtools "depth" implementation has a low base quality filter AND a low mapping quality filter for the entire read.

Does this account for the discrepancy?

[twaddlac]

It doesn't seem to. I've toggled the '-q -Q' parameters from 1 to -10000 and still didn't see any improvement, unless I'm misunderstanding the BAQ and mapQ values (higher = more confidence).

[Heisman]

It doesn't seem to. I've toggled the '-q -Q' parameters from 1 to -10000 and still didn't see any improvement, unless I'm misunderstanding the BAQ and mapQ values (higher = more confidence).

Try setting the mapping one to 0.

That said, I don't know why you are observing this. There are other ways to get coverage if that is your real goal (I prefer GATK's DepthOfCoverage).

[twaddlac]

I tried setting that to 0 and that didn't seem to make a difference. I tried to use GATK as well but it won't accept a bam file without read groups. I haven't tried it yet but putting a read group into the bam file doesn't sound too hard thought it is an inconvenience. Thanks for the advice, though!

[aggp11]

PicardTools AddorReplaceReadGroups does this easily and quickly. It takes a BAM file as input and you can provide the read group info. Following is the link:

http://picard.sourceforge.net/command-line-overview.shtml#AddOrReplaceReadGroups

[maivantan]

dear all,
Which command to calculate average of depth in samtools?
any suggestion please

[dpryan]

dear all,
Which command to calculate average of depth in samtools?
any suggestion please

depth (so, "samtools depth ..."). Please read the samtools manual next time.

[maivantan]

Yes, Thank you very much Dpryan,