Landmass avoidance using island

[eragonngo]

Hi Chad,

I am writing a navigating code for a vessel in seaway, and one of the requirements is to check if the next coordinate is land or sea. If I know a set of coordinates of subsea constructions, oil rigs, etc. How can I add these polygon area into the island function.

Thank you for your time and concern reading my question,

Sicnerely,

[eragonngo]

Would you recommend me with this procedure:

• Download the DEM from http://srtm.csi.cgiar.org/srtmdata/
• Read each GeoTIFF image using geoimread
• Run loop if it is grey scale (A value = -32768) then landmask matrix value = 0
• Merge landmask matrix

[chadagreene]

The mask isn't a very high resolution grid, so I'm not sure how valuable it will be for ship navigation. However, to customize the mask from another GeoTIFF I'd use interp2, or from a polygon use inpolygon.

[eragonngo]

Thank you for your details reply, I will use your suggestion then

[eragonngo]

Hi Chad, thank you so much for your recommendation.

I used georead to convert the geotiff and save the coordinate as well as the is_land matrix to -v7.3 MAT-file. The uncompressed file is 10GB per file and the whole world contains 48 file of this. I am using interp2 to read 3 lon and lat from same matrix but this process took 189 seconds to run.

Using a SSD, loading the mat file took only 35 seconds but interpolation took the 159 seconds rest for 3 coordinate. Would you recommend any other faster method beside interp2?