Remove R/rpy2 dependency; replace with cffdrs_py by conbrad · Pull Request #5176 · bcgov/wps

conbrad · 2026-03-02T21:52:55Z

Replaces all R/rpy2 calls in app/fire_behaviour/cffdrs.py with the pure-Python cffdrs_py package, eliminating the R runtime as a dependency.

Changes:

Rewrote all FWI and FBP wrappers in cffdrs.py to use cffdrs_py submodule imports
Removed CFFDRS singleton, r_importer.py, and CFFDRS pre-warming from startup
Removed rpy2 from pyproject.toml; added cffdrs git dependency (pinned to commit)
Removed R installation from base image Dockerfile, OpenShift build.yaml, and local dev Dockerfile
Improved None guards on bui_calc, initial_spread_index, fire_weather_index, and crown_fraction_burned; fixed drought_code silently substituting rh=0 when RH is None; fixed
length_to_breadth_ratio returning rather than raising CFFDRSException; added per-row error handling to hourly_fine_fuel_moisture_code
Updated 32 fba_calc tests (removed CFFDRS.instance() pre-warming); deleted test_r.py

Behavioural notes:

duff_moisture_code returns 0.0 (not ~0.256) when temperature < 1.1°C — cffdrs_py clamps temp to -1.1 before computing the drying rate (Eq. 16), zeroing it out. The R implementation did not apply this clamp.
cbh uses a fuel type default if it is None, this was handled internally before in the R library.

Closes #1926

Test Links:
Landing Page
MoreCast
Percentile Calculator
C-Haines
FireCalc
FireCalc bookmark
Auto Spatial Advisory (ASA)
HFI Calculator
SFMS Insights
Fire Watch

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

codecov · 2026-03-02T21:59:11Z

Codecov Report

❌ Patch coverage is 72.65625% with 35 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.78%. Comparing base (462ad8c) to head (04d5b76).

Files with missing lines	Patch %	Lines
.../packages/wps-api/src/app/fire_behaviour/cffdrs.py	72.22%	23 Missing and 12 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5176      +/-   ##
==========================================
- Coverage   68.80%   68.78%   -0.02%     
==========================================
  Files         392      391       -1     
  Lines       16373    16296      -77     
  Branches     1846     1815      -31     
==========================================
- Hits        11265    11210      -55     
+ Misses       4527     4515      -12     
+ Partials      581      571      -10

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dgboss · 2026-03-03T21:47:41Z

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

-                        FMC, SFC, PC, PDF, CC, CBH, ISI, output = "WSV")
-    WSV <- ifelse(GS > 0 & FFMC > 0, WSV0, WS)
+    Calculate the net effective windspeed (WSV).
+    WSV = Slopecalc(..., output="WSV") when GS > 0 and FFMC > 0, else WS.


:nit - Maybe remove this line of the comment, I don't think it's very helpful.

dgboss · 2026-03-03T22:02:56Z

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

+        fuel_type=fuel_type.value,
+        ffmc=ffmc,
+        bui=bui,
+        wsv=wsv if wsv is not None else 0,


I take it setting wsv = 0 here is equivalent to setting wsv = NULL in the R implementation?

dgboss · 2026-03-03T22:12:54Z

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

+    return buildup_index(dmc, dc)


 def rate_of_spread_t(fuel_type: FuelTypeEnum,


With the R implementation we used to check the value being returned from the calculation and would raise a CFFDRSException if necessary. We're now returning the value without a check. Is this safe and intentional? We're doing this in a number of places now.

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

sonarqubecloud · 2026-03-04T01:18:50Z

Quality Gate passed

Issues
6 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

brettedw · 2026-03-05T21:18:58Z

cbh uses a fuel type default if it is None, this was handled internally before in the R library.

Where does this happen? I think cffdrs_py still handles it internally

brettedw · 2026-03-05T21:23:30Z

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

+    calc_step: bool = False,
+    batch: bool = True,
+    hourly_fwi: bool = False,


These 3 args aren't used. I actually don't think hourly_fine_fuel_moisture_code is used in our code base. Do we need it?

brettedw · 2026-03-05T21:31:33Z

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

-    raise CFFDRSException("Failed to calculate CFB")
+    csi = critical_surface_intensity(fmc, cbh)
+    rso = surface_fire_rate_of_spread(csi, sfc)
+    return _crown_fraction_burned(ros, rso)


crown fraction burned is calculated differently for the C6 fuel type. cffdrs_py has a different function for that calculation, wondering if we should take care of that in this PR

brettedw · 2026-03-05T21:32:00Z

backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py

    return ws


 def flank_rate_of_spread(ros: float, bros: float, lb: float):


I think functions like this might be unnecessary

conbrad · 2026-03-05T22:55:36Z

cbh uses a fuel type default if it is None, this was handled internally before in the R library.

Where does this happen? I think cffdrs_py still handles it internally

backend/packages/wps-api/src/app/routers/fba_calc.py

brettedw · 2026-03-06T00:22:44Z

cbh uses a fuel type default if it is None, this was handled internally before in the R library.

Where does this happen? I think cffdrs_py still handles it internally

backend/packages/wps-api/src/app/routers/fba_calc.py

Took me awhile to figure out what was happening here, I was confused because R doesn't have fuel type default handling in those functions either, but it comes down to Python vs R math operations on NULL/None. Python will error, R won't.

Non-C6 fuel: ROS still comes from RSS (rate_of_spread.r (line 173)), so you often still get a numeric ROS.
C6 fuel: ROS depends on CFB/RSO, so it typically becomes NA (rate_of_spread.r (line 174)).

This is why C6 fuel type has built in 2 and 7m CBH on the front end

Regardless, all the calculations in FireCalc look the same to me

conbrad added 9 commits March 2, 2026 13:35

switch to cffdrs py

b969dfb

delete r reference raise CFFDRS exception

c760897

fix rh check

c214128

better error case handling

f7aeeb3

improve guard checks

a0b162f

improve cfb guards

f3c7af0

clamping comment

148b129

add boundary tests

1581c70

drop r from base image

896c86d

github-advanced-security bot found potential problems Mar 2, 2026

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backend/packages/wps-api/src/app/fire_behaviour/cffdrs.py Fixed Show fixed Hide fixed

conbrad added 3 commits March 2, 2026 14:31

keep behaviour

82dfd11

validate cbh

118be4f

use fuel type defaults for cbh

cbee151

conbrad requested review from brettedw and dgboss March 2, 2026 22:45

dgboss reviewed Mar 3, 2026

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conbrad added 2 commits March 3, 2026 17:14

Merge branch 'main' into task/cffdrs-py-no-r

e60218c

Formatting

04d5b76

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Remove R/rpy2 dependency; replace with cffdrs_py#5176

Remove R/rpy2 dependency; replace with cffdrs_py#5176
conbrad wants to merge 14 commits intomainfrom
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		return buildup_index(dmc, dc)


		def rate_of_spread_t(fuel_type: FuelTypeEnum,

		return ws


		def flank_rate_of_spread(ros: float, bros: float, lb: float):

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