Hi all,
I was testing r.slope.aspect with the “new” -n flag, also to include -e and -n flags in QGIS Processing, but -n flag is giving aspect values of flat areas as -9998, instead of -9999, when the precision choosed is CELL, and the output data type is CELL.
https://grass.osgeo.org/grass78/manuals/r.slope.aspect.html
I’ve tested with GRASS 7.6 (on Linux) and GRASS 7.8.2 (on Windows), both in the GUI and CLI.
(Tue Jan 28 11:19:40 2020)
r.slope.aspect -e -n --verbose elevation=SRTM_PT_25m@PERMANENT slope=SRTM_PT_25m_Slope_Deg_GRASS aspect=SRTM_PT_25m_Aspect_Std_GRASS precision=CELL
Percent complete…
Elevation products for mapset in <SRTM_PT_25m>
Min computed aspect 0.0000, max computed aspect 360.0000
Aspect raster map <SRTM_PT_25m_Aspect_Std_GRASS> complete
Min computed slope 0.0000, max computed slope 75.2970
Slope raster map <SRTM_PT_25m_Slope_Deg_GRASS> complete
(Tue Jan 28 11:20:24 2020) Comando terminado (43 sec)
r.info map=SRTM_PT_25m_Aspect_Std_GRASS@PERMANENT
±---------------------------------------------------------------------------+
| Map: SRTM_PT_25m_Aspect_Std_GRASS@ Date: Tue Jan 28 11:20:24 2020 |
| Mapset: PERMANENT Login of Creator: PedroVenancio |
| Location: SRTM_PT_25m |
| DataBase: D:\ICNF\Modelos_Combustivel_2018\Landscape_File\grass78 |
| Title: Aspect counterclockwise in degrees from east |
| Timestamp: none |
|---|
| Type of Map: raster Number of Categories: 360 |
| Data Type: CELL |
| Rows: 23200 |
| Columns: 11360 |
| Total Cells: 263552000 |
| Projection: ETRS89 / Portugal TM06 |
| N: 278000 S: -302000 Res: 25 |
| E: 164000 W: -120000 Res: 25 |
| Range of data: min = -9998 max = 360 |
| Data Source: |
| raster elevation file SRTM_PT_25m@PERMANENT |
| Data Description: |
| generated by r.slope.aspect |
| Comments: |
| aspect map elev = SRTM_PT_25m@PERMANENT |
| zfactor = 1.00 |
| min_slope = 0.000000 |
| r.slope.aspect --verbose -e -n elevation=“SRTM_PT_25m@PERMANENT” slo\ |
| pe=“SRTM_PT_25m_Slope_Deg_GRASS” aspect="SRTM_PT_25m_Aspect_Std_GRAS\ |
| S" format=“degrees” precision=“CELL” zscale=1.0 min_slope=0.0 |
| ±---------------------------------------------------------------------------+ |
| (Tue Jan 28 11:26:09 2020) Comando terminado (0 sec) |
Using the default precision as FCELL, all goes ok:
(Tue Jan 28 11:33:08 2020)
r.slope.aspect -e -n --verbose elevation=SRTM_PT_25m@PERMANENT slope=SRTM_PT_25m_Slope_Deg_GRASS_2 aspect=SRTM_PT_25m_Aspect_Std_GRASS_2
Percent complete…
Elevation products for mapset in <SRTM_PT_25m>
Min computed aspect 0.0000, max computed aspect 359.8096
Aspect raster map <SRTM_PT_25m_Aspect_Std_GRASS_2> complete
Min computed slope 0.0000, max computed slope 75.2970
Slope raster map <SRTM_PT_25m_Slope_Deg_GRASS_2> complete
(Tue Jan 28 11:34:01 2020) Comando terminado (53 sec)
(Tue Jan 28 11:34:27 2020)
r.info map=SRTM_PT_25m_Aspect_Std_GRASS_2@PERMANENT
±---------------------------------------------------------------------------+
| Map: SRTM_PT_25m_Aspect_Std_GRASS_ Date: Tue Jan 28 11:34:01 2020 |
| Mapset: PERMANENT Login of Creator: PedroVenancio |
| Location: SRTM_PT_25m |
| DataBase: D:\ICNF\Modelos_Combustivel_2018\Landscape_File\grass78 |
| Title: Aspect counterclockwise in degrees from east |
| Timestamp: none |
|---|
| Type of Map: raster Number of Categories: 360 |
| Data Type: FCELL |
| Rows: 23200 |
| Columns: 11360 |
| Total Cells: 263552000 |
| Projection: ETRS89 / Portugal TM06 |
| N: 278000 S: -302000 Res: 25 |
| E: 164000 W: -120000 Res: 25 |
| Range of data: min = -9999 max = 359.8097 |
| Data Source: |
| raster elevation file SRTM_PT_25m@PERMANENT |
| Data Description: |
| generated by r.slope.aspect |
| Comments: |
| aspect map elev = SRTM_PT_25m@PERMANENT |
| zfactor = 1.00 |
| min_slope = 0.000000 |
| r.slope.aspect --verbose -e -n elevation=“SRTM_PT_25m@PERMANENT” slo\ |
| pe=“SRTM_PT_25m_Slope_Deg_GRASS_2” aspect="SRTM_PT_25m_Aspect_Std_GR\ |
| ASS_2" format=“degrees” precision=“FCELL” zscale=1.0 min_slope=0.0 |
| ±---------------------------------------------------------------------------+ |
| (Tue Jan 28 11:34:28 2020) Comando terminado (0 sec) |
The elevation map I’m using is this one:
https://www.fc.up.pt/pessoas/jagoncal/srtm/SRTM_PT_25m.tif
As CELL is a 32 bit integer with a range from -2,147,483,647 to +2,147,483,647, -9999 should be fine to conform inside it.
Another issue I see is in r.info, that is showing the title as
| Title: Aspect counterclockwise in degrees from east
which is not correct in this case, as the -n flag was used.
Could these be bugs?
Thank you very much.
Best regards,
Pedro Venâncio