[GRASS-user] How to get the area of a polygon in a layer

[Kalindu Perera]

Hi Nikos,

Commands are as follows

*r.ros,*
r.ros --overwrite model=fuel_model at demomapset
moisture_1h=1hour_moisture at demomapset moisture_live=live_moisture at demomapset
velocity=wind_speed at demomapset direction=wind_direction at demomapset
slope=slope at demomapset aspect=aspect at demomapset
elevation=elevation at demomapset base_ros=my_ros.base max_ros=my_ros.max
direction_ros=my_ros.maxdir spotting_distance=my_ros.spotdist

*r.spread,*
r.spread --overwrite base_ros=my_ros.base at demomapset
max_ros=my_ros.max at demomapset direction_ros=my_ros.maxdir at demomapset
start=fire_origin at demomapset wind_speed=wind_speed at demomapset
output=spread_time_observed

*After entering; r.category spread_time_observed,*
[image: 1.png]

*After entering; r.report spread_time_observed units=c,p,*
[image: Screenshot from 2018-10-15 21-40-46.png]


Thank You
Best Regards
Kalindu Perera

On Mon, 15 Oct 2018 at 20:30, Nikos Alexandris <nik at nikosalexandris.net>
wrote:

> Please post the exact command you have used (copy-and-paste).
>
> Then, what does
> ```
> r.category spread_time_observed
> ```
>
> and what does
> ```
> r.report spread_time_observed units=c,p
> ```
>
> return?
>
> * Kalindu Perera <kkc199408 at gmail.com> [2018-10-15 16:01:38 +0530]:
>
> >Dear Nikos,
> >
> >We have used r.ros and r.spread commands for getting the wildfire
> >simulation.
> >After that, the output from the r.spread command is spread_time_observed
> >layer(This is the output from the simulation)
> >We use that layer as the input layer for the r.surf.area command.
> >
> >We got many area outputs from that command output and couldn't identify
> >what area gives the area of the "burned" area
> >* I have attached the output from running r.surf.area command as an
> >attachment.
> >
> >** Another question how we can extract only the "burned" area from the
> >spread_time_observed layer?
> >
> >Thanks a lot for the quick reply
> >Looking forward to more knowledge
> >
> >Best Regards
> >Kalindu Perera
> >
> >
> >On Mon, 15 Oct 2018 at 15:07, Nikos Alexandris <nik at nikosalexandris.net>
> >wrote:
> >
> >> * Kalindu Perera <kkc199408 at gmail.com> [2018-10-15 13:28:15 +0530]:
> >>
> >> >Dear all,
> >> >
> >> >We are doing wildfire simulation in Grass GIS. We need to compare the
> area
> >> >of 2 wildfire spreads after wildfire simulation ran. We tried to
> calculate
> >> >the area of the spread using r.surf.area module. But we couldn't
> identify
> >> >which is the area of the simulation from areas given from that. Could
> >> >anyone tell us how to get an area from spread like this?
> >>
> >> Dear Kalindu,
> >>
> >> please post exact commands you already tried.
> >>
> >> What are the simulation output maps?
> >> Fitst, what does `r.category` and `r.report` return when used for
> >> simulation
> >> maps?
> >>
> >> Then, maybe you need to "extract", each time, the "burned" area, then
> >> use `r.surf.area` on it?
> >>
> >> Nikos
> >>
> >>
> >>
>
>
>
> --
> Nikos Alexandris | Remote Sensing & Geomatics
> GPG Key Fingerprint 6F9D4506F3CA28380974D31A9053534B693C4FB3
>
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