Hello Professors and Seniors
I have tried to use grdtrack for the past three days but to no avail. I have my grd data (400_1_4_2_400.grd) as well as my xyz data (heatflow.xyz) that I want to use for sampling at every 10km. I want to use my grd data to track and sample some locations on my xyz data.
I tried to use many different parameters but to know avail.
One of the script I used is this
gmt grdtrack -G400_1_4_2_400.grd heatflow.xyz -Af -E93/-20,109/-1+i10u+d -R93/109/-20/-1 > heat.xyz
Another script is
gmt grdtrack -G400_1_4_2_400.grd heatflow.xyz -Af -E+o+d+i10u+l -R93/109/-20/-1 > heat.xyz
and also this out of many trials
$ gmt grdtrack -G400_1_4_2_400.grd heatflow.xyz -Af -E+oaz+d+i10ku+lu -R93/109/-20/-1 > heat.xyz
.
How can I use this gmt function to track and sample my grd data on the xyz data using a 10km sampling interval.
Many thanks Sir.
You cannot both specify a track to sample with -E and a track file to sample (heatflow.xyz). If as you say you want to sample the grid at the locations in the heatflowfile then no -E. If, on the other hand you wish to create sampling along a line every 10 km then use -E and specify +i10k. Your u unit is “survey foot”.
many thanks Prof. Sir, if I may ask based on your reply, what I wish to do is to sample the grid at the locations in the heatflowfile, what script must I use, because I haven’t used this GMT function grdtrack before until three days ago that I have been battling on it?
Sir, on the other hand if I wish to sample a line every 10km on my data , what script is to be used . This grdtrack function looks much complicated function to me in gmt. A friend just hinted me to use grdtrack.
Many thanks Sir.
Probably something like this to sample the grid at the heatflow locations
gmt grdtrack -G400_1_4_2_400.grd heatflow.xyz > heat_and_grid.xyz
Probably something like this to create line from coordinates and sample the grid every 10 km along the line. Here I am just picking a start and stop point for the line since I don’t know what you want so I picked a line from (95,3) to (105,-6):
gmt grdtrack -G400_1_4_2_400.grd -Af -E95/3/105/-6+i10k > grid_samplings.xyz
Prof. many thanks for your reply Sir, am grateful.
Sir the second gmt function returned an output but the first which is the very thing I want to do (i.e. sample the grid at the heatflow locations) did not show any result, I also went further to add other flags but still no result, what can I do to get the sampling done?
Hard to guess, but if you run
gmt grdinfo 400_1_4_2_400.grd
gmt gmtinfo heatflow.xyz
and post the output here then we will know a lot and can probably answer the question.
Three things from what I can see:
- Your heatflow.xyz file has a header records that does not start with “#”. Either add that leading character or use -hi1 to indicate skipping one record of arbitrary text. gmt info should then work.
- Without the gmt info output I cannot say for sure, but the little bit of heat flow records you show are all outside your grids domain (which is south of Equator).
- It looks like your grid is geographic degrees but it was not created that way (for instance, it says the name for x-coordinates is “x”, not “degrees_east”. Depending on how you or someone else made that file they forgot to add -fg or use -R93E/109E/17S/1S in the region to tell GMT this is geographic data.
If you can recreate the grid and add -fg when you do so, then that helps GMT to know what the data is. Also, add the comment (#) to your headflow header so it can be skipped.
and do the two commands I gave your work now then?