# Re: [ferret_users] Fwd: reading ascii in polar stereographic projection

Yes. The data I am working with has missing points. I believe they are missing data but instead of flagging them, the points were taken out of the file. So it is not a well-defined grid.
Derek

On Thu, May 7, 2009 at 5:55 PM, Ansley Manke wrote:
Hi Derek,
I'm not sure how that could happen.  For a well-defined polar stereographic grid, there has to be a complete set of longitudes and latitudes. There might be missing values for the data field, and those should have a missing-data flag, some particular value that marks that as bad data.  Maybe what you're starting with has just left out those points?

Derek Tsui wrote:
Thanks Ansley. I was wondering what would I do then if nx and ny isn't fixed in the data? When there is missing data.

For example, xindex = 1, yindex = 1:140 , but xindex = 2, yindex = 1:135

Derek

On Tue, May 5, 2009 at 6:17 PM, Ansley Manke wrote:
Hi Derek,
Your polar projection has coordinate data which is 2-dimensional, that is the longitudes and latitudes are defined on i,j index coordinate grid. At each i,j index pair there is a longitude, a latitude, and the value. Once you've accessed this data in Ferret, you'll use the curvilinear form of graphics calls to visualize the data.

What I would do is just write these three things to your ascii file, one longitude, latitude, value per record, with i varying fastest.  Then define a grid which has  x and y axes that are just the index values of the curvilinear coordinate variables:
yes? let nx = 140  ! or whatever the number of values is for your grid
yes? let ny = 80

yes? define axis/x=1:`nx`:1 xindex
yes? define axis/y=1:`ny`:1 yindex

yes? define grid/x=xindex/y=yindex grid_ij

yes? file/var="xlon,ylat,value"/grid=grid_ij  myfile.dat

yes? FILL value, xlon, ylat

Derek Tsui wrote:
Sorry I'm not sure if there were a response since I sent out the question before subscribing.

Thanks,
Derek
---------- Forwarded message ----------
From: Derek Tsui
Date: Wed, Apr 22, 2009 at 5:07 PM
Subject: reading ascii in polar stereographic projection
To: ferret_users@xxxxxxxx

I have a dataset in polar stereographic projection, ascii format, that I am trying to load into ferret and plot. It is 3 columns of data. longitutde, latitude, value. I can format it in any way.

I've tried the general script in the "Reading an ascii file: longitute latitute variable" thread but it doesn't seem to work in my case.

Any help would be much appreciated.

Thank you,
Derek