>From: Craig Motell <address@hidden> >Organization: University of Hawaii >Keywords: 199903240923.CAA06475 McIDAS ARAOPT Craig, >I would like to ask you some questions about the Mcidas function: ARAOPT. > >1) A sample program as the following: > >CALL ARAOPT(SAREA1,1,'SPAC',4) >CALL ARAOPT(SAREA1,1,'UNIT',LIT('BRIT')) This snippit combined with your earlier reference to the statement function 'getval' tells me that you are looking at nortel.pgm. >The keyword SPAC is defined by man pages as: > >'SPAC' spacing of output data (1, 2 or 4 bytes) > >Can you tell me if > >1)SPAC = number of bytes? Number of bytes that represent a pixel, yes. >2)why define the spacing of output data when this is used as an input >dataset? When you read the data, you will have to already specified the number of bytes per pixel that represents the data in the array into which you are reading information. REDARA (the routine that reads data out of an open AREA) calls MPIXEL to do a conversion if the output number of bytes per pixel ('SPAC') is different from the input number of bytes per pixel ('PREC'). >In the case of GOES-10 GVAR data we have 2byte integer a 4km, I suppose >then the 4 refers to size resolution? Where are you getting the '4 km' information (the correct answer depends on how you are interpreting this). If, for instance, you are using infrared data (given your desire to difference channels 4 and 5 below), then yes, the resolution of the data is 4 km AT THE SUB-SATELLITE POINT. >Lastly, if I wanted to create a new dataset which is a linear >combination of channel 4 and 5 (e.g., (ch4 - ch5)*cos(sun_angle) > >would I need to do something like: > >CALL OPNARA(outarea) ! a new file area number (e.g., AREA0006) >CALL ARAOPT(outarea,1,'UNIT',LIT('MINE')) You could do this, but then you would have to write a calibration routine that understood the 'MINE' calibration type when you go to interrogate the values from the file (using IMGPROBE, for instance). OK, I see that this is, in fact, what you are proposing to do below. >CALL ARAOPT(outarea,1,'PREC',2) You want the output data to be represented by two bytes per pixel. >Here I want to use a new calibration that I will set up, and >a byte precision of 2, assuming of coarse I already create, dir,nav,aux, >block. OK, then yes to the above. >3) Please just give me some comments on the things I will want to think >about before creating a new AREA file? For one thing, writing the calibration routine and getting understood by McIDAS is not trivial. It is not overwhelmingly hard; it is just not trivial. I assume that you need to write your own routine since routines like IMGOPER (ADDE) and IMGPRO (non-ADDE) do not have the sun angle as a readily available quantity; true? >Thankyou, What it seems like you are attempting to do looks interesting. Please don't hesitate to ask for information if you run into things which don't make sense (this is more fun than the mundane sorts of questions that we usually get :-). If I can't help, I will blast your question up to SSEC for them to comment on. Tom Yoksas
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