# comodo-sfilter v3.2.3

**Mercurial revision 5770:c90c3015e72d | 2026-05-22**

---

## Description

`comodo-sfilter` is a tool that **duplicates the functionality of `comodo-filter` for scalar fields**. It performs **DF-II IIR filtering** on input files. The tool takes one or more files as input and applies the specified filtering operations.

---

## Usage

```bash
comodo-sfilter file1 [file2 ...] [OPTIONS]
```

---

## Options


| Option                 | Description                                                                                                                                                                                      |
| ---------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `-h`, `--help`         | Display help and exit.                                                                                                                                                                           |
| `--control <file>`     | Path to a file containing control points. The file must be in ASCII format: the first line specifies the number of control points, followed by their coordinates (`longitude latitude [layer]`). |
| `--nodal=[yes|no]`     | Enable or disable nodal corrections. Default: `yes`.                                                                                                                                             |
| `-c <convention>`      | **Currently without effect.** Specify a convention (reserved for future use).                                                                                                                    |
| `-l <file>`            | Path to a file containing a list of input files. This list overrides any files provided as command-line arguments.                                                                               |
| `-g <file>`            | Path to the grid file.                                                                                                                                                                           |
| `-p <prefix>`          | Output prefix. Can be a folder path (e.g., `/output/`). **Recommended:** Use a different hard drive for filtering to improve performance.                                                        |
| `-s <date>`            | Start date for filtering in `dd/mm/yyyy` format.                                                                                                                                                 |
| `-f <date>`            | End date for filtering in `dd/mm/yyyy` format.                                                                                                                                                   |
| `-v <var1> [var2 ...]` | List of variables to filter.                                                                                                                                                                     |


---

## Examples

### **Basic Filtering**

Filter variables `ssh` and `tem` for files listed in `files.list`:

```bash
comodo-sfilter -l files.list -v ssh tem
```

### **Filtering with Start and End Dates**

Filter variable `ssh` for files between `01/01/2020` and `31/12/2020`:

```bash
comodo-sfilter -s 01/01/2020 -f 31/12/2020 -v ssh file1.nc file2.nc
```

### **Filtering with Control Points**

Filter variable `sal` using a grid file and control points:

```bash
comodo-sfilter -g grid.nc --control control_points.dat -v sal file1.nc
```

### **Filtering with Output Prefix**

Filter variable `XE` and save output to a specific directory:

```bash
comodo-sfilter -p /output/filtered/ -v XE file1.nc
```

### **Disable Nodal Corrections**

Filter variable `ssh` without nodal corrections:

```bash
comodo-sfilter --nodal=no -v ssh file1.nc
```

---

## Environment Variables

`comodo-sfilter` uses **OpenMP** (version 201511) for parallelization. The following environment variables can be used to control its behavior:


| Variable          | Description                                  |
| ----------------- | -------------------------------------------- |
| `OMP_NUM_THREADS` | Number of threads to use.                    |
| `OMP_SCHEDULE`    | Runtime schedule type and chunk size.        |
| `OMP_DYNAMIC`     | Enable or disable dynamic thread adjustment. |
| `OMP_NESTED`      | Enable or disable nested parallelism.        |


**Example:**

```bash
OMP_NUM_THREADS=6 comodo-sfilter -l files.list -v ssh
```

> **Note:** If running on a machine with high CPU load, limit the number of threads to the number of **free CPUs** to avoid performance degradation.

---

## Notes

1. **Input Files:**
  - Must be **comodo-compliant NetCDF** files.
  - The tool processes scalar fields only.
2. **Output:**
  - Filtered files are saved with the specified prefix (`-p`).
  - If no prefix is provided, output is saved in the current directory.
3. **Performance:**
  - For large datasets, use `-p` to output to a **different hard drive** to avoid I/O bottlenecks.
  - Adjust `OMP_NUM_THREADS` based on available CPU resources.
4. **Control Points:**
  - The control points file must be in ASCII format, with the first line specifying the number of points, followed by their coordinates (`longitude latitude [layer]`).
5. **Date Format:**
  - Dates must be provided in `dd/mm/yyyy` format for `-s` and `-f` options.

---

## See Also

- [`comodo-filter`](https://www.comodo-ocean.fr/) (for vector fields)
- [OpenMP Documentation](https://www.openmp.org/) (for environment variables and parallelization details)