# Incoherent gridline behaviour **URL:** \ **Category:** Q&A\ **Created:** [February 8, 2021, 10:00pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319 "2021-02-08T22:00:08Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 8, 2021, 10:00pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/1 "2021-02-08T22:00:08Z")
> On gmt v. 6.2.0\_bb0b2d9\_2020.12.14 with macOS Big Sur Hi, I’m trying to plot a time-series with two set of annotations for the y-axis using daily data. The primary axis is supposed to : - **not** annotate - tick every months - add a gridline every months The secondary axis is supposed to : - annotate every year - tick every year - add a gridline every year I hoped to have a thicker line for the secondary grid lines, but if it’s too complicated, I can also not use it as it is redundant with the primary ones (once per year). At any rate, at first I tried this : ```auto gmt grdimage ${region} ${projection} $FILE?var -Bxa20f10g10 -Bpyf1Og1O -Bsya1Yf1Yg1Y -BWSen ``` as well as `12O` `12o` `1y`… The annotations are fine, the ticks seem to be too … but the grid lines are either shifted and inconsistently spaced or plotted daily (or so it seems). Do you have a suggestion ? See picture : On left : `-Bpyf1o -Bsya1Y` On right : `-Byf1og12y` ![Screenshot 2021-02-08 at 17.05.23](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/915a7cd22ab18ae6651f74a7e86f03198d0bf7ea.png) ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 8, 2021, 11:14pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/2 "2021-02-08T23:14:47Z")
using psbasemap appears to work: > gmt psbasemap -R0/100/2020-06-01T/2021-06-01T -JX10c/10cT -Bxa20f10g10 -Bpyf1Og1O -Bsya1Yf1Yg1Y -BWSen --MAP\_GRID\_PEN\_PRIMARY=thinner,grey --MAP\_GRID\_PEN\_SECONDARY=thin,black -png test > > ![test](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/fb1cda01a2434785e8188fc1b8f440cef7713944.png) > I didn’t expect that grdimage will do something different, but I didn’t have any file here to try. > Is it possible to share some simple data to test it? > using gmt 6.2.0\_68e0098\_2021.01.19 ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 8, 2021, 11:32pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/3 "2021-02-08T23:32:39Z")
Sure … Sorry for the delay … I had to extract a sample and upload it on a tiers service : > **[Dropbox](https://www.dropbox.com/s/g73jngb2p0zrzbj/sample_data.nc?dl=0)** The data are Sea-Surface Temperature averaged in the Pacific equatorial band (so it has the dimension of longitude x time) lon1 = 110 lonN = 280 time1 = 1980-01-01 timeN = 1984-01-01 (I think , I truncated it bluntly) the variable to plot is eqb\_nc\_sst ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 1:22am UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/4 "2021-02-09T01:22:08Z")
appears that it get a wrong TIME\_EPOCH: > $ gmt grdinfo sample\_data.nc > grdinfo [WARNING]: TIME\_EPOCH format is invalid. Default assumed. > grdinfo [WARNING]: A correct format has the form [-]yyyy-mm-ddThh:mm:ss[.xxx] > grdinfo [WARNING]: or (using ISO weekly calendar) yyyy-Www-dThh:mm:ss[.xxx] > grdinfo [WARNING]: An example of a correct format is: 2000-01-01T12:00:00 > grdinfo [WARNING]: Time units [days since 0000-01-00 00:00:00.0 +0000]] in grid not recognized, defaulting to gmt.conf settings. > sample\_data.nc: Title: > sample\_data.nc: Command: > sample\_data.nc: Remark: > sample\_data.nc: Gridline node registration used [Cartesian grid] > sample\_data.nc: Grid file format: nf = GMT netCDF format (32-bit float), CF-1.7 > sample\_data.nc: x\_min: 110 x\_max: -80 x\_inc: 0.25 name: longitude n\_columns: 681 > sample\_data.nc: y\_min: 0 y\_max: 126144000 y\_inc: 86400 name: time [days since 0000-01-00 00:00:00.0 +0000] n\_rows: 1461 > sample\_data.nc: v\_min: 0 v\_max: 0 name: eqb\_nc\_sst > sample\_data.nc: scale\_factor: 1 add\_offset: 0 > sample\_data.nc: format: classic I try to convert to xyz and back to grid to set the TIME\_EPOCH, but I get only NaN for the Z value: > gmt grd2xyz “sample\_data.nc?eqb\_nc\_sst” | gmt xyz2grd -R110/280/1980-01-01T/1984-01-01T -I0.25/86400 -f0f,1t -Gtest.nc Anyway, to test the grid, I could use this test.nc garbage: > gmt makecpt -Crainbow \> test.cpt > gmt grdimage test.nc -R110/280/1981-01-01T/1983-01-01T -JX10c/10cT -Ctest.cpt -Bxa20f10g10 -Bpyf1Og1O -Bsya1Yf1Yg1Y -BWSen --MAP\_GRID\_PEN\_PRIMARY=thinner,grey --MAP\_GRID\_PEN\_SECONDARY=thin,black -png test appears that the grid is ok, a primary every months and a secondary every year: ![test](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/997628f9455fbe535cb9d24df89a01283113987f.png) what command (including values) are you using? It could be useful to know the gmt defaults that you are using. ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 9, 2021, 1:35am UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/5 "2021-02-09T01:35:30Z")
Hum weird, maybe the time goes from 0 to length(time) with ```auto gmt gmtset TIME_EPOCH 1980-01-01 ``` ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 10:33am UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/6 "2021-02-09T10:33:40Z")
after some adjust in the netcdf file and using: > gmt makecpt -T294/304/1 \> test.cpt resulting: ![test](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/57ca54e92f58bdacd140e4ec3fb9adaa17ba9bb8.png) It appears to me that the grid is ok, a primary every months and a secondary every year. ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 9, 2021, 3:15pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/7 "2021-02-09T15:15:25Z")
Using the same kind of data (relative time `TIME_EPOCH 1980-01-01`) ```auto gmt grdimage -R$lon1a/$lon1b/$day1/$day2 -JX${w1}cd/-${height}ct $FILE?eqb_cl_sst -Bxa20f10g10 -Bpyf1O -Bsya1Yf1Y -BWSen ``` Gives expected result. Any `g` addition to either `Bpy` or `Bsy` fill the plot with gridlines every day (unit) instead of wanted `O` or `Y`. Could it be related to the issue I reported with `math` [on Github](https://github.com/GenericMappingTools/gmt/issues/4771#issue-804042384) ? ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 4:02pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/8 "2021-02-09T16:02:57Z")
here I didn’t have ploblems do add g to either Bpy or Bsy, as I showed before. I think I get your example right here: > $ gmt math -o0 -T1980-01-01T/2019-12-31T/4y T = > 1980-01-01T00:00:00.000000000 > 1984-01-01T00:00:00.000000000 > 1988-01-01T00:00:00.000000000 > 1992-01-01T00:00:00.000000000 > 1996-01-01T00:00:00.000000000 > 2000-01-01T00:00:00.000000000 > 2004-01-01T00:00:00.000000000 > 2008-01-01T00:00:00.000000000 > 2012-01-01T00:00:00.000000000 > 2016-01-01T00:00:00.000000000 could you share your defaults? > gmt defaults \> defaults.txt What I have here is: [defaults.txt](https://forum.generic-mapping-tools.org/uploads/short-url/rZzvM6HJ7Q573yUYZcmsjZeEYtj.txt) (5.1 KB) Note that I used “T” in -JX10c/10cT to specify a time axes and appears that you used “t”. Could it be the problem? What exactly is your -JX${w1}cd/-${height}ct ? ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 9, 2021, 4:35pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/9 "2021-02-09T16:35:53Z")
> [@MarceloBanik](#): > > What exactly is your -JX${w1}cd/-${height}ct These are numeric values calculated with `bc` … not an issue really I see that you’re using the “stable” version (GMT6.1), maybe a bug in dev6.2 ? I’ll take a moment this afternoon to compare your default file … thanks 🙂 ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 4:50pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/10 "2021-02-09T16:50:54Z")
working with gmt 6.2.0\_68e0098\_2021.01.19: > $ gmtswitch 6.2.0;gmt --version;gmt math -o0 -T1980-01-01T/2019-12-31T/4y T = > 6.2.0\_68e0098\_2021.01.19 > 1980-01-01T00:00:00.000000000 > 1984-01-01T00:00:00.000000000 > 1988-01-01T00:00:00.000000000 > 1992-01-01T00:00:00.000000000 > 1996-01-01T00:00:00.000000000 > 2000-01-01T00:00:00.000000000 > 2004-01-01T00:00:00.000000000 > 2008-01-01T00:00:00.000000000 > 2012-01-01T00:00:00.000000000 > 2016-01-01T00:00:00.000000000 ---
**Author:** ![maxrjones](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/maxrjones/32/2698_2.png) [@maxrjones](https://forum.generic-mapping-tools.org/u/maxrjones)\ **Post date:** [February 9, 2021, 5:11pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/11 "2021-02-09T17:11:09Z")
I think you’re probably using different OS’s. When I build 6.2.0\_68e0098\_2021.01.19 on MacOS `gmt math -o0 -T1980-01-01T/2019-12-31T/4y T =` does not work and gives the same bug as reported recently on GitHub. ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 9, 2021, 6:05pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/12 "2021-02-09T18:05:28Z")
@maxrjones : back to the `-Bg options` problem, do you think it is also an OS issue ? Nothing really unusual between my default parameters / script and the ones @MarceloBanik shared to help me. ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 7:31pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/13 "2021-02-09T19:31:26Z")
gmt grdimage test.nc -R110/280/1981-11-01T/1982-02-01T -JX10cd/10cT -Ctest.cpt -Bxa20f10g10 -Bpyf1Og1O -Bsya1Yf1Yg1Y -BWSen --MAP\_GRID\_PEN\_PRIMARY=thinner,grey --MAP\_GRID\_PEN\_SECONDARY=thin,black --TIME\_INTERVAL\_FRACTION=0.1 -png test1 results: ![test1](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/09ce472fad1bbebd9186d2c59177c908a5f00c4d.png) changing -R110/280/1981-11-01T/1982-02-01T to -R110/280/373420800/381369600 > gmt grdimage test.nc -R110/280/373420800/381369600 -JX10cd/10cT -Ctest.cpt -Bxa20f10g10 -Bpyf1Og1O -Bsya1Yf1Yg1Y -BWSen --MAP\_GRID\_PEN\_PRIMARY=thinner,grey --MAP\_GRID\_PEN\_SECONDARY=thin,black --TIME\_INTERVAL\_FRACTION=0.1 --TIME\_UNIT=s --TIME\_EPOCH=1970-01-01T00:00:00 -png test2 results: ![test1](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/09ce472fad1bbebd9186d2c59177c908a5f00c4d.png) changing -JX10cd/10cT to -JX10cd/10ct > gmt grdimage test.nc -R110/280/373420800/381369600 -JX10cd/10ct -Ctest.cpt -Bxa20f10g10 -Bpyf1Og1O -Bsya1Yf1Yg1Y -BWSen --MAP\_GRID\_PEN\_PR > IMARY=thinner,grey --MAP\_GRID\_PEN\_SECONDARY=thin,black --TIME\_INTERVAL\_FRACTION=0.1 --TIME\_UNIT=s --TIME\_EPOCH=1970-01-01T00:00:00 -png test3 results: ![test3](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/89d919cc7cc00e59a043f4612b656735a1b592e7.png) what I suspect is a grid every day. Then I suspect you could try use -JX${w1}cd/-${height}cT ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 9, 2021, 8:13pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/14 "2021-02-09T20:13:40Z")
> [@MarceloBanik](#): > > Then I suspect you could try use -JX${w1}cd/-${height}cT That works ! Thanks. It is strange because the script used to work fine in GMT5… I guess modern mode is more rigorous about this. 🤔 ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 8:59pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/15 "2021-02-09T20:59:40Z")
I think it should have worked with -JX${w1}cd/-${height}ct. So it appears to be a bug. ---
**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\ **Post date:** [February 9, 2021, 10:01pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/16 "2021-02-09T22:01:35Z")
I dont think it is a but. Capital T is required if you want an axis to be temporal. ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 9, 2021, 10:06pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/17 "2021-02-09T22:06:44Z")
This is weird though With `-J[...]ct` (and timestamps given relative to TIME\_EPOCH) everything works except for `-Byg[..]` (no problem with x). The gridlines are systematically plotted at “unit”. With `-J[...]cT` (and timestamps given in absolute format) everything works. ---
**Author:** ![MarceloBanik](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/marcelobanik/32/479_2.png) [@MarceloBanik](https://forum.generic-mapping-tools.org/u/MarceloBanik)\ **Post date:** [February 9, 2021, 10:58pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/18 "2021-02-09T22:58:02Z")
from [https://docs.generic-mapping-tools.org/latest/gmt.html#r-full](https://docs.generic-mapping-tools.org/latest/gmt.html#r-full) For calendar time coordinates you may either give (a) relative time (relative to the selected TIME\_EPOCH and in the selected TIME\_UNIT; append t to -JX|x) Then I think that -R110/280/373420800/381369600 -JX10cd/10ct --TIME\_UNIT=s --TIME\_EPOCH=1970-01-01T00:00:00 should have worked. ---
**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\ **Post date:** [February 10, 2021, 12:22am UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/19 "2021-02-10T00:22:19Z")
I agree that it says that in the docs. I will try to learn why the 1O gets (probably) converted to double and gives 1 (second). ---
**Author:** ![PlanetGus](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/planetgus/32/303_2.png) [@PlanetGus](https://forum.generic-mapping-tools.org/u/PlanetGus)\ **Post date:** [February 10, 2021, 10:51pm UTC](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319/20 "2021-02-10T22:51:41Z")
@pwessel, I’m not sure we’re talking about the same thing… I have 2 set of data where time starts at 0 (relative to `TIME_EPOCH 1980-01-01` , `TIME_UNIT d`) - A netcdf file (`grdimage`) - A text file (`plot`) When I try to plot my data I do ```auto # Case 1 (wanted) gmt grdimage -R0/360/1980-01-01/1984-01-01 -JX10cd/-10ct file.nc"?var" -Bxa20f10g10 -Bpyf1og1o -Bsya1yf1yg1y -BWSen gmt plot tmp.txt -W2,black -Gred -Sc -t50 # Case 2 (not ideal) gmt grdimage -R0/360/0/1461 -JX10cd/-10ct file.nc"?var" -Bxa20f10g10 -Bpyf1og1o -Bsya1yf1yg1y -BWSen gmt plot tmp.txt -W2,black -Gred -Sc -t50 # Case 3 gmt grdimage -R0/360/1980-01-01/1984-01-01 -JX10cd/-10cT file.nc"?var" -Bxa20f10g10 -Bpyf1og1o -Bsya1yf1yg1y -BWSen gmt plot tmp.txt -W2,black -Gred -Sc -t50 ``` ## Case 1 : JX()d/()t (x : geo-degrees , y: relative time) `-R` is given with absolute time regardless. Both `grdimage` and `plot` are displayed as expected, except for the grid lines on y-Primary and y-Secondary axis. They are too dense and completely fill the picture (TIME\_UNIT probably switched in seconds) Apart from the grid line, everything is correct. (NB x-axis grid lines are fine too) ## Case 2 : same `-R` is given with relative time. It makes no difference compared to **Case 1** , so I’d rather stick to the **Case 1** as the input format doesn’t require additional calculation. ## Case 3 : JX()d/()T (x : geo-degrees , y: absolute time) -R is given with absolute time. `grdimage` is still fine. The gridlines appear correctly, but `plot` is off-grid. [Next page](https://forum.generic-mapping-tools.org/t/incoherent-gridline-behaviour/1319.md?page=2)