<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">Hi Folks</span></font><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">I am trying to check for null values in input raster files using Python Ctypes interfaces.</span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">First of all I am not sure how you do this using Ctypes. Heres what I am doing:</span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">...............</span></font></div><div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">for row_n in range(rows):</span></font></div><div><span class="Apple-tab-span" style="white-space:pre"><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"> </span></font></span><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"># read a row of raster data into memory, then print it</span></font></div><div><span class="Apple-tab-span" style="white-space:pre"><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"> </span></font></span><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">Rast_get_row(in_fd, in_rast, row_n, data_type)</span></font></div><div><span class="Apple-tab-span" style="white-space:pre"><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"> </span></font></span><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"># Check for null value</span></font></div><div><span class="Apple-tab-span" style="white-space:pre"><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"> </span></font></span><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">for col_n in range(cols):</span></font></div></div><div><span class="Apple-tab-span" style="white-space:pre"><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"> </span></font></span><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">if(Rast_is_d_null_value(pointer(c_double(in_rast[col_n])))):</span></font></div><div><span class="Apple-tab-span" style="white-space:pre"><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"> </span></font></span><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">in_rast[col_n] = 0.0</span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"><br></span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">But this does not work as for all null values in the input raster map I am getting some value of "-2147483648" in my input buffer so the above check is failing. What am i doing wrong here and whats the best way to trap null values in input raster using Ctypes libraries? I suspect that value of "-2147483648" is probably some sort of string/ascii representation of "Null" but am not sure whats causing this conversion and how to avoid that and just trap null values plain and simple. </span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"><br></span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">Any suggestions from all of you will be most welcome!!</span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;"><br></span></font></div><div><font class="Apple-style-span" size="5"><span class="Apple-style-span" style="font-size: 18px;">BTW I have done this effectively in C and also in Ctyoes while writing out grass raster but still clueless about the input part.</span></font></div><div><br></div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><br></div></body></html>