polar2grid projections

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kathys
Posts: 374
Joined: Tue Jun 22, 2010 4:51 pm

polar2grid projections

Post by kathys »

From arb - copied from VIIRS SDR section - posted 30 May 2013:

Here's a quick tip for changing the projections available with the polar2grid script.

You can find the projections configured in this file:

polar2grid/ShellB3/lib/python2.7/site-packages/polar2grid-1.0.0-py2.7.egg/polar2grid/grids/grids.conf

The format is documented but to give you a start, if you prefer to work by example, here's three new ones:

This one specifies an output resolution of 400m:
polar_north_atlantic, proj4, +proj=stere +datum=WGS84 +ellps=WGS84 +lat_0=90 +lat_ts=55.0 +lon_0=0,None,None,400,-400,None,None

This one specifies the output dimensions as 3200 pixels:
polar_north_atlantic_ql,proj4, +proj=stere +datum=WGS84 +ellps=WGS84 +lat_0=90 +lat_ts=55.0 +lon_0=0,3200,3200,None,None,None,None

This one is Cassini (satellite) projection and specifies an extent in metres plus the output dimensions as 800 pixels:
msg_ql, proj4, +proj=cass +lat_0=54.00366 +lon_0=-2.547855 -te -1500000 -1500000 1500000 1500000,800,800,None,None,None,None
kathys
Posts: 374
Joined: Tue Jun 22, 2010 4:51 pm

Re: polar2grid projections

Post by kathys »

Replay posted by daveh 4 June 2013

Awesome, thanks for diving into the code like that. In the next version of polar2grid (coming soon) we will make it possible for users to add their own grid configuration files on the command line. That way you can organize them the way you want and you don't have to change any internal package files.
arb
Posts: 14
Joined: Wed May 29, 2013 12:41 pm

Re: polar2grid projections

Post by arb »

I'm not sure my Cassini example is going to work - it uses the "-te" syntax from a gdal command line which is not proj4 syntax.
You're going to have to specify all values rather than None. There's a helper program in the new polar2grid called p2g_grid_helper.sh.
msg_672_ql, proj4, +proj=cass +lat_0=54.00366 +lon_0=-2.547855,672,672,4464.285715,-4464.285715,-1500000,1500000
msg_800_ql, proj4, +proj=cass +lat_0=54.00366 +lon_0=-2.547855,800,800,3750,-3750,-1500000,1500000
msg_2017_ql, proj4, +proj=cass +lat_0=54.00366 +lon_0=-2.547855,2017,2017,1487.357462,-1487.357462,-1500000,1500000
davidh
Posts: 92
Joined: Tue Jun 04, 2013 11:19 am

Re: polar2grid projections

Post by davidh »

arb, you're right. Polar2grid will only support valid PROJ.4 strings. So you'll have to do some math to get extents like that.
johnson.peter68
Posts: 1
Joined: Fri Jan 24, 2014 12:33 pm

Re: polar2grid projections

Post by johnson.peter68 »

An ellipsoid is defined by equatorial radius and eccentricity. The ellipsoid used in the Hughes software assumes a radius of 3443.992 nautical miles or 6378.273 km and an eccentricity (e) of 0.081816153.
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