[GRASS-dev] Re: GRASS Python Ctypes: Write Raster produces No null file error!!

[Sudipta Sarkar]

Folks
On close observation made some changes to the fragment of code below on the suspicion that I was not setting null values correctly or passing pointers right so the modified code is now given below but still I get the same error of: ERROR: No null file for <madresult.0>

Please give me some suggestions as I have a deadline approaching.

Modified code:
MA.resize(bands,rows,cols)
    for b in range(bands):
	ofn = "madresult." + str(b)
	out_fd = Rast_open_new(ofn,DCELL_TYPE)
	if out_fd < 0:
	    grass.fatal(_("Unable to create raster map <%s>") % ofn)
    	out_rast = Rast_allocate_d_buf()
	#out_rast = cast(c_void_p(out_rast), ptype)
   	for row_n in range(rows):
	    for col_n in range(cols):
		#if math.isnan(MAD[b,row_n,col_n]):
		if (Rast_is_d_null_value(pointer(c_double(MAD[b,row_n,col_n])))):
		    Rast_set_d_null_value(pointer(c_double(out_rast[col_n])),1)
		else:
		    out_rast[col_n] = MA[b,row_n,col_n]
	    Rast_put_row(out_fd,out_rast,DCELL_TYPE)
	G_free(out_rast)
	Rast_close(out_fd)

Humble regards


On Apr 11, 2011, at 8:25 AM, Sudipta Sarkar wrote:

Dear List Users,

Please help me solve the following, I am entirely new to the whole Python-GRASS-Ctypes issue so please bear with me. 

I am trying to develop an application using Python Ctypes hooks to GRASS C libraries. Have done most of the part but getting stuck in the end where i try to write off my output file as GRASS raster. I am giving the relevant part below along with the error I am getting:

    ptype = POINTER(c_float)
    MA.resize(bands,rows,cols)
    for b in range(bands):
	ofn = "madresult." + str(b)
	out_fd = Rast_open_new(ofn,FCELL_TYPE)
	if out_fd < 0:
	    G_fatal_error("Unable to create raster map <%s>", ofn)
    	out_rast = Rast_allocate_buf(FCELL_TYPE)
	out_rast = cast(c_void_p(out_rast), ptype)
   	for row_n in range(rows):
	    for col_n in range(cols):
		if math.isnan(MA[b,row_n,col_n]):
		    Rast_set_null_value(out_rast[col_n],1,FCELL_TYPE)
		else:
		    out_rast[col_n] = MA[b,row_n,col_n]
	    Rast_put_row(out_fd,out_rast,FCELL_TYPE)
	G_free(out_rast)
	Rast_close(out_fd)
	
where MA is a numpy.ndarray, bands, rows and cols are all integer type variables and are self explanatory i believe. 

When it comes to executing the line "Rast_close(out_fd)" I am getting the error: "ERROR: No null file for <madresult.0>"

How do I write the null file? I have some experience in developing GRASS raster modules in C and there I never had to write any null file explicitly so whats going wrong over here? Any help from all you GRASS pioneers will be deeply appreciated. 

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