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Re: [ferret_users] vector/aspect question

Hi Jozef -

As a general rule, I never use vector/asp, because it distorts the true direction of the vectors.

Without the /asp qualifier, a vector pointing northeast in fact represents a wind towards the northeast. With /asp, it might not. For example, suppose you are plotting a region that is truly square (say 5S-5N, 55W-45W), but set the window aspect ratio to be rectangular (for example like the default window). In this case, the plot will be stretched in the E-W direction (i.e., a map of the coastline will be distorted). If you plot vectors with /asp, the vectors will be comparably distorted, which I think is misleading. If you plot vectors without /asp, then the vectors will all have their correct directions; however, vectors that are in reality parallel to the coast will not appear to be. The lesson here is to always make maps of vectors in a viewport with the correct aspect ratio!

! in the example above:
set win/asp=`55-45/10`:axis

The main exception I would make to the above is in plotting vectors where the aspect ratio is necessarily distorted, like vertical sections.

Billy K

On Mar 27, 2006, at 12:16 AM, Jozef.Syktus@nrm.qld.gov.au wrote:

I am plotting winds at 850 hPa u,v using vector from GCM model output, the data is in lat long coordinates (T63). Should I use vector/aspect option or just vector?


Jozef Syktus

Climate Impacts and Natural Resource Systems
Department of Natural Resources, Mines and Water
80 Meiers Rd., Indooroopilly Qld 4068 Australia

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