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Rob Patro committed Feb 9, 2025
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Expand Up @@ -184,7 +184,11 @@ corresponding to the `minimap2` parameter `-N`) can be specified with the comman

### Alignmment-based input

In alignment-based mode, `oarfish` processes pre-computed alignments of hte read to the transcriptome. The input should be a `bam` format file, with reads aligned using [`minimap2`](https://github.com/lh3/minimap2) against the _transcriptome_. That is, `oarfish` does not currently handle spliced alignment to the genome. Further, the output alignments should be name sorted (the default order produced by `minimap2` should be fine). _Specifically_, `oarfish` relies on the existence of the `AS` tag in the `bam` records that encodes the alignment score in order to obtain the score for each alignment (which is used in probabilistic read assignment), and the score of the best alignment, overall, for each read. ### Choosing `minimap2` alignment options Since the purpose of `oarfish` is to estimate transcript abundance from a collection of alignments to the target transcriptome, it is important that the alignments are generated in a fashion that is compatible with this goal. Primarily, this means that the aligner should be configured to report as many optimal (and near-optimal) alignments as exist, so that `oarfish` can observe all of this information and determine how to allocate reads to transcripts. We recommend using the following options with `minimap2` when aligning data for later processing by `oarfish` * For ONT data (either dRNA or cDNA): please use the flags `--eqx -N 100 -ax map-ont` For PacBio data: please use the flags `--eqx -N 100 -ax pacbio` **Note (1)**: It may be worthwile using an even larger `N` value (e.g. the [TranSigner manuscript](https://www.biorxiv.org/content/10.1101/2024.04.13.589356v1.full) recommends `-N 181`). A larger value should not diminish the accuracy of `oarfish`, but it may make alignment take longer and produce a larger `bam` file.
In alignment-based mode, `oarfish` processes pre-computed alignments of hte read to the transcriptome. The input should be a `bam` format file, with reads aligned using [`minimap2`](https://github.com/lh3/minimap2) against the _transcriptome_. That is, `oarfish` does not currently handle spliced alignment to the genome. Further, the output alignments should be name sorted (the default order produced by `minimap2` should be fine). _Specifically_, `oarfish` relies on the existence of the `AS` tag in the `bam` records that encodes the alignment score in order to obtain the score for each alignment (which is used in probabilistic read assignment), and the score of the best alignment, overall, for each read.

### Choosing `minimap2` alignment options

Since the purpose of `oarfish` is to estimate transcript abundance from a collection of alignments to the target transcriptome, it is important that the alignments are generated in a fashion that is compatible with this goal. Primarily, this means that the aligner should be configured to report as many optimal (and near-optimal) alignments as exist, so that `oarfish` can observe all of this information and determine how to allocate reads to transcripts. We recommend using the following options with `minimap2` when aligning data for later processing by `oarfish` * For ONT data (either dRNA or cDNA): please use the flags `--eqx -N 100 -ax map-ont` For PacBio data: please use the flags `--eqx -N 100 -ax pacbio` **Note (1)**: It may be worthwile using an even larger `N` value (e.g. the [TranSigner manuscript](https://www.biorxiv.org/content/10.1101/2024.04.13.589356v1.full) recommends `-N 181`). A larger value should not diminish the accuracy of `oarfish`, but it may make alignment take longer and produce a larger `bam` file.

**Note (2)**: For very high quality PacBio data, it may be most appropriate to use the `-ax map-hifi` flag in place of `-ax pacbio`. We are currently evaluating the effect of this option, and also welcome feedback if you have experiences to share on the use of data aligned with these different flags with `oarfish`.

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