[GRASS-user] East/West Horizons Giving Negative Numbers

[Stefan Blumentrath]

Hi Ashley,

The possibility to return negative horizon values was introduced here:
https://github.com/OSGeo/grass/commit/688d5885557f22c7ea6618dcac3ddfbfc764731a#diff-5ce8290f429502e23efaf9ebdc18bd2b

The output with the d-flag is azimuth degree (-90 – 90, where 0 is parallel with the focal cell).
So, from my understanding, negative values indicate horizon height below the cell it is computed from.

Maybe the manual could be a bit more specific here…?

Cheers
Stefan

From: grass-user <grass-user-bounces at lists.osgeo.org> On Behalf Of Ashley Cale
Sent: tirsdag 26. mai 2020 21:16
To: grass-user at lists.osgeo.org
Subject: [GRASS-user] East/West Horizons Giving Negative Numbers

  Hello Everyone!

Can help me figure out what's wrong with my east and west horizon calculations?

I am trying to compute my east and west horizon angle from my DEM using the command r.horizon. My output raster contains negative numbers and it's my understanding that the range of output values should be between 0 and 360. I used -d to make sure that my output is in degrees rather than radians.

Can anyone help me solve this problem? Or point me in the right direction?

Thank you for the help!
Ashley

Here is the r.info<http://r.info/> output from my generated east horizon raster.
 |----------------------------------------------------------------------------|
 |                                      |
 |  Type of Map: raster        Number of Categories: 0        |
 |  Data Type:  FCELL                           |
 |  Data Units:  degrees       Vertical datum: (none)        |
 |  Rows:     7532                            |
 |  Columns:   5860                            |
 |  Total Cells: 44137520                          |
 |    Projection: UTM (zone 10)                      |
 |      N: 4543151.24515692  S: 4317194.98362237  Res: 29.99950366  |
 |      E: 759846.34683197  W: 584057.70444841  Res: 29.99806184   |
 |  Range of data:  min = -90 max = 78.47394               |
 |                                      |
 |  Data Description:                            |
 |  generated by r.horizon                         |
 |                                      |
 |  Comments:                                |
 |  r.horizon -d elevation="dem30m at PERMANENT" direction=0 start=0.0 end=\  |
 |  360.0 output="east" distance=1.0 file="-"                |
 |                                      |
 |  Horizon view from azimuth angle 0.00 degrees CCW from East       |
 |                                      |
 +----------------------------------------------------------------------------+

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