nearneighbor search radius unit ignored

[anbj]

If not given, the default nearneighbor search radius unit is in meter (http://gmt.soest.hawaii.edu/doc/latest/nearneighbor.html). Specifying the unit (e) makes nearneighbor think its dealing with geographic data. Both cases should be in cartesian data.

nearneighbor -I.2 dat -S20e -R0/100/0/100 -Vd -Gwith_e_debug.nc

outputs

...
nearneighbor [INFORMATION]: Your distance unit (e) implies geographic data; -fg has been set.
...

The diff between the two commands nearneighbor -I.2 dat -S20e -R0/100/0/100 -Vd -Gwith_e_debug.nc and nearneighbor -I.2 dat -S20e -R0/100/0/100 -Vd -Gwith_e_debug.nc (one with the UNIT specified and the other not) gives

$ bash nearneighbor_unit.sh
45,51c45,49
< nearneighbor [DEBUG]: Map distance calculation will be using great circle approximation with authalic auxiliary latitudes and authalic (R_2) radius = 6371007.1809 m, in meter.
< nearneighbor [INFORMATION]: Your distance unit (e) implies geographic data; -fg has been set.
< nearneighbor [DEBUG]: Map distance calculation will be using great circle approximation with authalic auxiliary latitudes and authalic (R_2) radius = 6371007.1809 m, in meter.
< nearneighbor [DEBUG]: Geographic input grid, longitudes span less than 360
< nearneighbor [DEBUG]: Chosen boundary condition for all edges: geographic
< nearneighbor [DEBUG]: Geographic input grid, longitudes span less than 360
< nearneighbor [DEBUG]: Object ID 0 : Registered Grid Memory Reference 194c3f0 as an Input resource with geometry Surface [n_objects = 1]
---
> nearneighbor [DEBUG]: Map distance calculation will be Cartesian
> nearneighbor [INFORMATION]: Cartesian input grid
> nearneighbor [DEBUG]: Chosen boundary condition for all edges: natural
> nearneighbor [INFORMATION]: Cartesian input grid
> nearneighbor [DEBUG]: Object ID 0 : Registered Grid Memory Reference 12fd3f0 as an Input resource with geometry Surface [n_objects = 1]
60c58
< nearneighbor [INFORMATION]: Max node-search half-widths are: half_x = 1, half_y = 251
---
> nearneighbor [INFORMATION]: Max node-search half-widths are: half_x = 100, half_y = 100
70c68
< nearneighbor [INFORMATION]: Processed record       1599
---
> nearneighbor [INFORMATION]: Processed record       1786
73c71
< nearneighbor [DEBUG]: Object ID 2 : Registered Grid File with_e_debug.nc as an Output resource with geometry Surface [n_objects = 3]
---
> nearneighbor [DEBUG]: Object ID 2 : Registered Grid File without_e_debug.nc as an Output resource with geometry Surface [n_objects = 3]
76c74
< nearneighbor [INFORMATION]: Writing grid to file with_e_debug.nc
---
> nearneighbor [INFORMATION]: Writing grid to file without_e_debug.nc
81c79
< nearneighbor [INFORMATION]: No valid values in grid [with_e_debug.nc]
---
> nearneighbor [DEBUG]: packed z-range: [0,9.78769]
83,85c81,83
< nearneighbor [INFORMATION]: 0 nodes were assigned an average value
< nearneighbor [INFORMATION]: 2452 nodes failed sector criteria and 248549 nodes had no neighbor points (all set to NaN)
< nearneighbor [DEBUG]: gmtapi_garbage_collection: Destroying object: C=0 A=0 ID=0 W=Input F=Grid M=Memory Reference S=Unused P=194c3f0 N=(null)
---
> nearneighbor [INFORMATION]: 247350 nodes were assigned an average value
> nearneighbor [INFORMATION]: 3651 nodes failed sector criteria and 0 nodes had no neighbor points (all set to NaN)
> nearneighbor [DEBUG]: gmtapi_garbage_collection: Destroying object: C=0 A=0 ID=0 W=Input F=Grid M=Memory Reference S=Unused P=12fd3f0 N=(null)

Script to produce the diff with included dummy_data.txt:

nearneighbor -I.2 dummy_data.txt -S20e -R0/100/0/100 -Vd -Gwith_e_debug.nc 2> with_e_debug.log
nearneighbor -I.2 dummy_data.txt -S20 -R0/100/0/100 -Vd -Gwithout_e_debug.nc 2> without_e_debug.log
diff with_e_debug.log without_e_debug.log

rm with_e_debug.log without_e_debug.log with_e_debug.nc without_e_debug.nc

gmt clear history 

• Version of GMT: 6.0.0_821bce2

[welcome]

👋 Thanks for opening your first issue here! Please make sure you filled out the template with as much detail as possible. We appreciate that you took the time to contribute!

[PaulWessel]

If your data are Cartesian, why are you giving a unit? The e, k, M, and other units are only needed if you are providing geographic data in lon,lat format. For Cartesian data the increment is used as is.

[anbj]

I'm confused. So e.g. -S500e is not the same as -S500? Why is e then the default unit?

[PaulWessel]

It is the Default unit for geographic data. For Cartesian data there cannot possibly be a default units since how would we know if it is time, distance, weight, chemical concentrations, etc etc.

[anbj]

Alright. Dont know why I got so confused about this.