创建一个NetCDF文件，其数据被屏蔽以仅保留着陆点 [英] Create a NetCDF file with data masked to retain land points only

问题描述

我已在研究生中使用basemap.gs脚本屏蔽了NetCDF文件.这是我使用口罩得到的:

I have masked a NetCDF file using basemap.gs script in grads. Here is what I got using the mask:

所以，我想获得一个仅包含大陆数据的NetCDF文件，有人可以帮我吗?

So, I would like to obtain a NetCDF file which only contains the continental data, can anyone help me with this?

推荐答案

如果我正确理解了这个问题，则希望拥有一个netcdf文件，该文件的所有值都设置为在海点上丢失(即_Fillvalue).如果是这样，可以从命令行中找到两种解决方案:

If I have understood the question correctly, the desire is to have a netcdf file with all the values set to missing (i.e. _Fillvalue) over the sea points. If so there are two solutions from the command line:

一种方法是使用CDO创建陆地-海洋遮罩，然后将所有海洋点设置为丢失:

One way is to use CDO to create a land-sea mask and then set all the sea points to missing:

cdo -f nc2 setctomiss,0 -gtc,0 -remapcon,your_data_.nc -topo seamask.nc

• 其中 remapcon 将地形重新映射到数据文件的域和分辨率.
• 当内置地形大于海平面时，gtc会产生1.
• 然后setctomiss将所有零"点都设置为丢失.
• where remapcon remaps the topography to the domain and resolution of your data file.
• The gtc,produces 1 when the built in topography is greater then sea level.
• Then the setctomiss sets all the "zero" points to missing.

您现在可以使用它来屏蔽您的数据文件:

You can now use this to mask your datafile:

cdo mul datafile.nc seamask.nc masked_datafile.nc

但是，在某些情况下，我发现重新映射过程在边缘留下了海洋"数据的痕迹，在这种情况下，为了安全起见，您可以使用第二种方法:

However, in some circumstances I have found that the remapping process leaves traces of "ocean" data around the edges, in this case to be safer you can use the second method:

从此thredds服务器以1 km的分辨率下载netcdf数据文件，以获取到海洋的距离":

Download the netcdf data file for "distance to ocean" at 1km resolution from this thredds server: https://pae-paha.pacioos.hawaii.edu/thredds/ncss/dist2coast_1deg_land/dataset.html

然后，您可以掩盖海洋一定距离内的任何点以安全使用，这可能会掩盖少量的陆地数据.

Then you can mask out any points within a certain distance of the ocean to play it safe, at the expense of possibly masking out a small amount of land data.

我首先将距离文件重新映射到目标分辨率:

I remapped the distance file to the target resolution first:

cdo remapbil,your_data.nc distance.nc remap_dist.nc

然后屏蔽(例如，在这种情况下，距离海岸5公里以内的所有点，此文件中的海点已经丢失")并相乘

then mask (e.g. in this case all points within 5km of the coast, sea points are already "missing" in this file) and multiply

cdo mul your_data.nc -gtc,5 remap_dist.nc masked_data.nc

如前所述，这比较安全一些，有些困难，但是可能会掩盖一些陆地数据.

As said, this is a little safer, a little more longwinded, but may mask some land data.

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