Describe the bug

The i.in.spotvgt module has multiple issues that either break functionality or silently produce invalid (NULL) outputs. The distinct problems encountered during usage and debugging:

1. Incorrect condition: if f < 2:

Present in create_VRT_file() function
Problematic Line:

if f < 2:

throws a TypeError because f is a list.

2. Incorrect SM file name generation

Present inside the -a flag block
Problematic Line:

qname = spotname.replace("NDV", "SM")
qfile = os.path.join(spotdir, qname)

Error encountered:
ERROR 4: 0001_SM: No such file or directory
This occurred because the code was looking for 0001_SM but the file was named 0001_SM.HDF.

3. Incorrect use of list for stdin in gs.write_command()

Problematic Line:

rules = [
    r + "\n"
    for r in [
        "8 50 50 50",
        ...
    ]
]
gs.write_command("r.colors", map=smfile, rules="-", stdin=rules)

Error:
TypeError: can only accept types str and bytes

4. Critical: gs.use_temp_region() caused all outputs to be NULL

Issue:

gs.use_temp_region()

This created a temporary region, and all operations like r.mapcalc and g.rename operated within that temp region, never flushing the result to the main mapset. This led to:

• r.info showing metadata

• but r.univar showing:

  n: 0
  min: nan
  

Impact:
This was the root cause of the final map being completely NULL despite all steps succeeding.

To reproduce

1. Use i.in.spotvgt on a valid HDF + LOG + SM input.

2. Run the module normally (with or without -a).

3. Check the final raster with:

   r.univar test_output

4. Observe that it has n: 0 and is completely NULL.

Expected behavior

The output raster should contain actual NDVI values remapped from DN using:

NDVI = 0.004 * DN - 0.1

Instead, it silently creates an empty map.

System description

• Operating System: Windows Subsystem for Linux (WSL)
• GRASS GIS version: 8.4
• details about further software components
  • GRASS 8.5.0dev
  • Python verison: 3.10.12
  • wxPython version: 4.2.2

Root Causes

1. Incorrect condition in create_VRT_file(), f should be checked using len(f) < 2 to avoid a TypeError.

2. Status map file path was missing the .HDF extension, leading to a file not found error. This can be resolved by appending + ".HDF" to the filename.

3. stdin was incorrectly passed as a list to gs.write_command(), which expects a single string. Joining the list into a string will fix the issue.

4. gs.use_temp_region() caused output maps to remain in a temporary region, making them effectively NULL. Removing this line will allow the maps to be persisted correctly.

I will be adding the patched code soon, testing all the changes locally.