pyheclib

Documentation: nzahasan.github.io/pyheclib

Read and write HEC-DSS files from Python.

HEC-DSS is the database format used by HEC-HMS, HEC-RAS and other tools from the US Army Corps of Engineers' Hydrologic Engineering Center. pyheclib works with DSS version 7 files. It bundles the official HEC-DSS C library for Linux (x86_64), macOS (Apple Silicon, macOS 14+) and Windows (x64).

DSS version 6 files are not supported. Convert them to version 7 with HEC-DSSVue first.

Install

pip install pyheclib

Requires Python 3.8 or newer. Depends on numpy and pandas.

Quick start

Every record is a Python object that holds its pathname, data and metadata. Create a record, write it to a file, and read gives you the same kind of object back.

Open a file

import numpy as np
import pandas as pd
import pyheclib as phl

dss_file = phl.open("example.dss")     # opens the file, or creates it

You can also use it as a context manager: with phl.open("example.dss") as dss_file: ...

Regular time series

The interval comes from the E part of the pathname, e.g. 1HOUR, 15MINUTE, 1DAY, 1MONTH. Missing values are NaN.

# from a list of values and the time of the first value
precip = phl.RegularTs("/DEMO/GAGE/PRECIP//1DAY/OBS/", values=[0.0, 12.5, 48.0, 3.1, 0.0],
                       start="2020-01-14", unit="MM", type="PER-CUM")
dss_file.write(precip)

# from a pandas Series
hours = pd.date_range("2020-01-14 01:00", periods=96, freq="h")
flow = pd.Series(40 + 50*np.exp(-((np.arange(96) - 40) / 12.0)**2), index=hours)
flow.iloc[70:76] = np.nan
dss_file.write(phl.RegularTs.from_series("/DEMO/OUTLET/FLOW//1HOUR/OBS/", flow, unit="CFS", type="INST-VAL"))

# read the whole series (leave the D part empty)
rts = dss_file.read("/DEMO/OUTLET/FLOW//1HOUR/OBS/")          # -> RegularTs
print(rts.unit, rts.type, rts.interval, rts.start)            # CFS INST-VAL 1HOUR 2020-01-14 01:00:00
series = rts.to_series()                                      # pandas Series indexed by time

# or just a time window
window = dss_file.read("/DEMO/OUTLET/FLOW//1HOUR/OBS/", start="2020-01-15 12:00", end="2020-01-15 18:00")

Irregular time series

Use an E part that starts with IR- (or ~), e.g. IR-MONTH. Times are stored to the second. Writing replaces any stored values inside the time span of the new record.

stage = phl.IrregularTs("/DEMO/OUTLET/STAGE//IR-MONTH/OBS/",
                        times=pd.to_datetime(["2020-01-14 08:13:00", "2020-01-15 07:30:15", "2020-01-16 16:45:00"]),
                        values=[3.1, 4.6, 3.4], unit="FT", type="INST-VAL")
dss_file.write(stage)

its = dss_file.read("/DEMO/OUTLET/STAGE//IR-MONTH/OBS/")      # -> IrregularTs
its.times, its.values, its.to_series()

Paired data

All curves share one x array. y has one row per curve. labels (optional) names the curves.

h = np.linspace(0, 12, 49)
rating = phl.PairedData("/DEMO/OUTLET/STAGE-FLOW///RATING/", x=h,
                        y=np.vstack([5.2*h**1.80, 5.6*h**1.75, 6.1*h**1.70]),
                        x_unit="FT", y_unit="CFS", labels=["2018", "2019", "2020"])
dss_file.write(rating)

pd_rec = dss_file.read("/DEMO/OUTLET/STAGE-FLOW///RATING/")   # -> PairedData
pd_rec.n_curves, pd_rec.labels
df = pd_rec.to_dataframe()                                    # index: x, one column per curve

Gridded data

data is a 2d numpy array, stored as float32:

• the first row is the northern-most row (north-up)
• NaN means no data
• xll, yll is the lower-left corner of the grid, in the grid's coordinate system
• the D and E parts are the start and end time; leave both empty for grids that don't change over time (e.g. a DEM)

yy, xx = np.mgrid[0:90, 0:140]
field = (38*np.exp(-(((xx - 85)/22.0)**2 + ((yy - 40)/14.0)**2))).astype(np.float32)
field[((xx - 70)/68.0)**2 + ((yy - 45)/44.0)**2 > 1] = np.nan       # outside the basin

grid = phl.GriddedData("/SHG/DEMO/PRECIP/15JAN2020:0000/15JAN2020:0600/RADAR/", field,
                       cell_size=2000.0, xll=-180000.0, yll=1320000.0, unit="MM", type="PER-CUM",
                       grid_type="ALBERS", srs_name="SHG", time_zone="UTC")
dss_file.write(grid)

g = dss_file.read("/SHG/DEMO/PRECIP/15JAN2020:0000/15JAN2020:0600/RADAR/")   # -> GriddedData
g.data.shape, g.cell_size, g.extent, g.lower_left_cell, g.start_time

Pathnames and the catalog

A DSS pathname has six parts: /A/B/C/D/E/F/. DssPath lets you work with the parts. Anywhere a pathname is expected, you can pass a DssPath or a plain string.

path = phl.DssPath("/DEMO/OUTLET/FLOW/01JAN2020/1HOUR/OBS/")
path.C                        # 'FLOW'
path.replace(F="SIM")         # DssPath('/DEMO/OUTLET/FLOW/01JAN2020/1HOUR/SIM/')
path.without_date()           # DssPath('/DEMO/OUTLET/FLOW//1HOUR/OBS/')
phl.DssPath.from_parts(A="DEMO", C="STAGE-FLOW", F="RATING")

dss_file.catalog()                      # every record (a long time series is split into blocks)
dss_file.catalog(condensed=True)        # one path per time series, D part = date range,
                                        # e.g. 01JAN2020-01MAR2020
dss_file.catalog("/DEMO/*/FLOW/*/*/*/", condensed=True, with_types=True)
dss_file.read(dss_file.catalog(condensed=True)[0])   # a condensed path reads the whole series

Find and delete

Use * at the start or end of any pathname part as a wildcard. delete returns the paths it removed.

dss_file.find("/DEMO/*/*/*/*/OBS/")                    # every OBS record in DEMO
dss_file.find("/*/*/STAGE*/*/*/*/")                    # STAGE and STAGE-FLOW records

dss_file.delete("/DEMO/OUTLET/STAGE-FLOW///RATING/")   # one record
dss_file.delete("/DEMO/OUTLET/FLOW//1HOUR/OBS/")       # a whole time series (all blocks)
dss_file.delete("/SHG/*/*/*/*/*/")                     # everything with A part SHG
dss_file.close()

Limitations

• Quality flags are read when present, but not written.
• Gridded data is always stored as float32.
• Only DSS version 7 files.

Quick reference

A compact summary of the API, useful for scripts and AI coding agents.

import pyheclib as phl

phl.open(filename) -> DssFile                 # creates the file if missing; context manager
DssFile.write(record)                         # replaces existing data at that path
DssFile.read(path, start=None, end=None)      # -> RegularTs | IrregularTs | PairedData | GriddedData
DssFile.catalog(path_filter="", condensed=False, with_types=False) -> list[DssPath]
DssFile.find(path) -> list[DssPath]           # '*' wildcard at start/end of a part
DssFile.delete(path) -> list[DssPath]         # raises KeyError if nothing matches
DssFile.record_type(path) -> int              # 105 regular ts, 115 irregular ts, 205 paired, 4xx grid
DssFile.close()

RegularTs(path, values, start, unit="", type="INST-VAL", time_zone="")
    .interval  .times  .to_series()  RegularTs.from_series(path, series, unit, type)
IrregularTs(path, times, values, unit="", type="INST-VAL", time_zone="")
    .to_series()  IrregularTs.from_series(path, series, unit, type)
PairedData(path, x, y, x_unit="", y_unit="", labels=[])
    .n_curves  .to_dataframe()  PairedData.from_dataframe(path, df, x_unit, y_unit)
GriddedData(path, data, cell_size, xll, yll, unit="", type="INST-VAL",
            grid_type="SPECIFIED", srs_wkt="", srs_name="", origin=(0, 0), time_zone="")
    .shape  .extent  .lower_left_cell  .start_time  .end_time

DssPath(path) | DssPath.from_parts(A=, B=, C=, D=, E=, F=)
    .A .. .F  .parts()  .replace(**parts)  .without_date()

Rules worth knowing:

• type is one of INST-VAL, INST-CUM, PER-AVER, PER-CUM, FREQ.
• grid_type is one of UNDEFINED, HRAP, ALBERS, SPECIFIED.
• Regular time series: the E part sets the interval. Irregular: E part starts with IR- or ~.
• Leave the D part empty to read a whole time series; use start / end for a window.
• Missing values are NaN for all record types.
• HEC-DSS log output is set by the DSS_MESSAGE_LEVEL environment variable (0 = none to 15 = debug); default and fallback is 1 (critical only).
• Gridded xll, yll must line up with origin in whole multiples of cell_size.

Tools

Command-line tools in tools/:

python3 tools/dss_browser.py file.dss [--port 8765] [--no-browser]   # browse a file in your web browser
python3 tools/dss_catalog.py file.dss [filter] [--condensed]         # list records
python3 tools/dssrec2csv.py file.dss pathname out.csv                # export one record to csv

The browser opens one or more files in tabs (or drag files onto the page). Search records by text or by part (B=GAGE C=FLOW*), view metadata, statistics, a graph or table of the data, and download a record as csv. Each record has its own link (/?file=1&path=/A/B/C/D/E/F/).

Examples and notebooks

• examples/example.dss has every record type to try things on (rebuild it with python3 examples/make_example_dss.py).
• examples/make_readme_figures.py draws the figures in this README.
• Notebooks, each writes records, reads them back and checks the result: regular time series, irregular time series, paired data, gridded data, catalog, paths and delete.

Development

git clone https://github.com/nzahasan/pyheclib && cd pyheclib
pip install -r requirements.txt
python3 setup.py build_ext --inplace    # rebuild after editing src/*.pyx or src/*.pxd
pytest                                  # also runs the code in this README

Code layout:

• pyheclib/records.py: record classes
• pyheclib/dsspath.py: DssPath
• pyheclib/dssfile.py: open and DssFile
• src/_core.pyx: thin Cython wrapper around the HEC-DSS C API

Resources

• Documentation
• HEC-DSS
• HEC-DSSVue, a desktop viewer for DSS files