Global Mapper v25.0

Why does adding a TIN change the watershed generation DEM resolution?

JSL
JSL Global Mapper UserTrusted User

I’ve found that sometimes, if I add a TIN layer to an underlying elevation DEM and then try to generate a watershed, GM automatically increases the resolution on the “Generate watershed” command screen by a huge amount.  For example, the first attachment is a screenshot of a Generate Watershed command screen for a SRTM 90m DEM, with the resolution automatically set by GM at the DEM elevation point resolution.   The second attachment is the Generate Watershed command screen for the same DEM plus a TIN layer—you can see how the resolution jumped. 

 

What’s odd is that not every TIN causes the resolution to jump, and different TINs create different resolutions.  I’ve been getting around the problem by copying the original resolution of the DEM to a text document, and pasting it into the command screen, but it would be nice if GM would automatically “remember” the resolution of the most recent Generate Watershed command.

 

Thanks for any help.


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Answers

  • Thea_bmg
    Thea_bmg Global Mapper User
    The automatic resolution will take into account the highest resolution data in the workspace, so if the TIN has a higher resolution than your SRTM data, the resolution will jump higher.   One option would be to turn off your high resolution layer in the overlay control center before performing your watershed analysis.
  • JSL
    JSL Global Mapper User Trusted User
    Ah, that makes sense.  However, I need to have the TIN included in the watershed analysis, so I guess I'll just go on changing the resolution by hand.  It would be nice if there was an option for the watershed resolution to default to the most recently used number, though.