I want to project the shadows from a DSM raster.

Is it possible to iterate the grass function r.sunmask.datetime over a list from a csv file composed with interest dates(month/day) and time (hours from 9:00 to 18:00) along the year?

2 Answers 2


Yes, of course.

Actually the power of GRASS really shines when you need to perform repetitive tasks in a loop. The specific answer depends on how your CSV is formatted, what operating system you're working on, and what command shell you prefer. For example: If I had a CSV that looks like:


and if I wanted to write a loop using the Linux bash shell:

while IFS=, read dy mo yr hr mn;
    do output=`sunmask_$yr_$mn_$dy_$hr_$mn`;
    r.sunmask elevation=<your DSM> year=$yr month=$mn day=$dy hour=$hr minute=$mn output=$output;

The above can be re-written also for a windows cmd shell, and could be easily ported to python. Pay attention to the timezone parameter. (Refer to the man page for details...)

  • Hi Micha, I'm working in windows environment. Is the script you wrote suitable to it? Feb 6, 2020 at 7:13
  • Hint: if r.sunmask is too slow in computing shadows, consider r.sun (grass.osgeo.org/grass78/manuals/…)
    – markusN
    Feb 6, 2020 at 21:05
  • Indeed it's very slow but I solved it by another way with earthpy library. Feb 7, 2020 at 7:30

I solved it by another way with earthpy library. You'll need a dataframe with daily and hourly azimut and altitude. Here's the script:

def hillshade (index):
    altitude = df.altitude[index]
    azimut = df.azimut[index]
    return ep.plot_bands(
    es.hillshade(elevation, azimuth = azimut, altitude = altitude),

for i in df.index:

That will print a raster for every date and time you have in your data frame.

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