<div dir="ltr"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><p>What do you mean by "new raster"? What is supposed to be in it
and how should its extents, CRS etc be defined?</p></div></blockquote><div>Well, I might want to create the extents + crs based on a different raster, but I also might want to create it based on some user input.</div><div>For example if I write a module that starts from a vector layer and generates a raster layer processing it.</div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><p>Do you have existing data that you want to use to create it? Or
why is a constant value raster not what you want?</p></div></blockquote><div>I agree that 99% of the times I will start from an existing raster layer from which I take extent, resolution and crs.<br></div><div>And I am ok with using the processing toolbox to create a new raster initialized with novalues.</div><div><br></div><div>The problem I posed in the first place (with the code snippet) is that if I modify the raster using a QgsRasterBlock, the result is not correct.</div><div>In the snippet I am taking values from one raster and copy it into the new raster in certain conditions. But the result is not the expected one.</div><div>So my first question was if I am doing something wrong. Because I expect a portion following isolines to be set to novalue, but instead I get just a noisy raster layer.</div><div><br></div><div>Thanks,</div><div>Andrea</div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>
<p>If you want to base it on an existing raster, best use a raster
calculator to create a plain copy.<br>
</p>
<p>Cheers, Hannes<br>
</p>
<div>Am 09.05.23 um 08:28 schrieb andrea
antonello via QGIS-User:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hello,<br>
<div>I am trying to find out the best workflow to create a new
raster.</div>
<div>As an example I take an existing elevation model raster and
loop over it to set values between 1500 and 2000 to novalue
and write the result to a new raster.</div>
<div><br>
</div>
<div>This is the only way I found to do so:</div>
<div><br>
</div>
<div>
<div style="color:rgb(0,0,0);font-family:"Droid Sans Mono","monospace",monospace;font-size:14px;line-height:19px;white-space:pre-wrap"><div><span style="color:rgb(0,128,0)"># create new raster with novalues between 1500 and 2000</span></div><div><span style="color:rgb(0,16,128)">dataType</span> = <span style="color:rgb(0,16,128)">dtmLayer</span>.<span style="color:rgb(121,94,38)">dataProvider</span>().<span style="color:rgb(121,94,38)">dataType</span>(<span style="color:rgb(9,134,88)">1</span>)</div><div><span style="color:rgb(0,16,128)">crs</span> = <span style="color:rgb(38,127,153)">QgsCoordinateReferenceSystem</span>(<span style="color:rgb(163,21,21)">'EPSG:3003'</span>)</div><div><span style="color:rgb(0,16,128)">params</span> = {</div><div> <span style="color:rgb(163,21,21)">'EXTENT'</span>: <span style="color:rgb(0,16,128)">dtmLayer</span>.<span style="color:rgb(121,94,38)">extent</span>(),</div><div> <span style="color:rgb(163,21,21)">'TARGET_CRS'</span>: <span style="color:rgb(0,16,128)">crs</span>,</div><div> <span style="color:rgb(163,21,21)">'PIXEL_SIZE'</span>: <span style="color:rgb(0,16,128)">dtmLayer</span>.<span style="color:rgb(121,94,38)">rasterUnitsPerPixelX</span>(),</div><div> <span style="color:rgb(163,21,21)">'NUMBER'</span>: -<span style="color:rgb(9,134,88)">9999.0</span>,</div><div> <span style="color:rgb(0,128,0)"># 'OUTPUT_TYPE': dataType,</span></div><div> <span style="color:rgb(163,21,21)">'OUTPUT'</span>: <span style="color:rgb(38,127,153)">QgsProcessing</span>.<span style="color:rgb(0,16,128)">TEMPORARY_OUTPUT</span></div><div>}</div><div><span style="color:rgb(0,16,128)">newRaster</span> = <span style="color:rgb(38,127,153)">processing</span>.run(<span style="color:rgb(163,21,21)">'qgis:createconstantrasterlayer'</span>, <span style="color:rgb(0,16,128)">params</span>)[<span style="color:rgb(163,21,21)">'OUTPUT'</span>]</div><div><span style="color:rgb(0,16,128)">newRasterLayer</span> = <span style="color:rgb(38,127,153)">QgsRasterLayer</span>(<span style="color:rgb(0,16,128)">newRaster</span>, <span style="color:rgb(163,21,21)">'temp'</span>, <span style="color:rgb(163,21,21)">'gdal'</span>)</div><div><span style="color:rgb(0,16,128)">newRasterProvider</span> = <span style="color:rgb(0,16,128)">newRasterLayer</span>.<span style="color:rgb(121,94,38)">dataProvider</span>()</div>
<div><span style="color:rgb(0,16,128)">block</span> = <span style="color:rgb(38,127,153)">QgsRasterBlock</span>(<span style="color:rgb(0,16,128)">dataType</span>, <span style="color:rgb(0,16,128)">cols</span>, <span style="color:rgb(0,16,128)">rows</span>)</div><div>
</div><div><span style="color:rgb(175,0,219)">for</span> <span style="color:rgb(0,16,128)">row</span> <span style="color:rgb(0,0,255)">in</span> <span style="color:rgb(38,127,153)">range</span>(<span style="color:rgb(0,16,128)">rows</span>):</div><div> <span style="color:rgb(175,0,219)">for</span> <span style="color:rgb(0,16,128)">col</span> <span style="color:rgb(0,0,255)">in</span> <span style="color:rgb(38,127,153)">range</span>(<span style="color:rgb(0,16,128)">cols</span>):</div><div> <span style="color:rgb(0,16,128)">point</span> = <span style="color:rgb(0,16,128)">dtmLayer</span>.<span style="color:rgb(121,94,38)">dataProvider</span>().<span style="color:rgb(121,94,38)">transformCoordinates</span>(<span style="color:rgb(38,127,153)">QgsPoint</span>(<span style="color:rgb(0,16,128)">col</span>, <span style="color:rgb(0,16,128)">row</span>), <span style="color:rgb(0,16,128)">transformType</span>)</div><div> <span style="color:rgb(0,16,128)">value</span>, <span style="color:rgb(0,16,128)">res</span> = <span style="color:rgb(0,16,128)">dtmLayer</span>.<span style="color:rgb(121,94,38)">dataProvider</span>().<span style="color:rgb(121,94,38)">sample</span>(<span style="color:rgb(38,127,153)">QgsPointXY</span>(<span style="color:rgb(0,16,128)">point</span>.<span style="color:rgb(121,94,38)">x</span>(), <span style="color:rgb(0,16,128)">point</span>.<span style="color:rgb(121,94,38)">y</span>()), <span style="color:rgb(9,134,88)">1</span>)</div><div> </div><div> <span style="color:rgb(175,0,219)">if</span> <span style="color:rgb(0,16,128)">res</span> <span style="color:rgb(0,0,255)">and</span> <span style="color:rgb(0,16,128)">value</span> != -<span style="color:rgb(9,134,88)">9999.0</span>:</div><div> <span style="color:rgb(175,0,219)">if</span> <span style="color:rgb(0,16,128)">value</span> < <span style="color:rgb(9,134,88)">1000</span> <span style="color:rgb(0,0,255)">or</span> <span style="color:rgb(0,16,128)">value</span> > <span style="color:rgb(9,134,88)">2000</span>:</div><div> <span style="color:rgb(0,16,128)">block</span>.<span style="color:rgb(121,94,38)">setValue</span>(<span style="color:rgb(0,16,128)">row</span>, <span style="color:rgb(0,16,128)">col</span>, <span style="color:rgb(0,16,128)">value</span>)</div><div>
</div><div><span style="color:rgb(0,16,128)">newRasterProvider</span>.<span style="color:rgb(121,94,38)">setEditable</span>(<span style="color:rgb(0,0,255)">True</span>)</div><div><span style="color:rgb(0,16,128)">newRasterProvider</span>.<span style="color:rgb(121,94,38)">writeBlock</span>(<span style="color:rgb(0,16,128)">block</span>, <span style="color:rgb(0,16,128)">band</span>=<span style="color:rgb(9,134,88)">1</span>)</div><div><span style="color:rgb(0,16,128)">newRasterProvider</span>.<span style="color:rgb(121,94,38)">setEditable</span>(<span style="color:rgb(0,0,255)">False</span>)</div></div>
</div>
<div><br>
</div>
<div><br>
</div>
<div>This code has two main issues:</div>
<div>1. if I uncomment the line containing OUTPUT_TYPE, I am
getting an error about the type passed. But I can't find the
right type needed there, it should be the one taken from the
original provider.</div>
<div>2. the resulting raster is scrambled as if there was a
shift in the setting of the values. But the
QgsRasterBlock seems to be built correctly (rows, cols) and
the values set properly (col, row).<br>
3. in the above example, the dtmLayer has an epsg 3033 crs and
when loaded manually into QGIS, it is recognized. But when I
read the layer's metadata crs with pyQGIS , it is not able to
read it and tells me it is invalid. </div>
<div><br>
</div>
<div>Has anyone a hint about what I am doing wrong? </div>
<div><br>
</div>
<div>Thanks,</div>
<div>Andrea</div>
<div><br>
</div>
<div><br>
</div>
</div>
<br>
<fieldset></fieldset>
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