<div dir="ltr">Hi Ming,<div><br></div><div>There are no vector layers in WMS. It's for imagery only. </div><div><br></div><div>Perhaps you are interested in WFS instead?</div><div><br></div><div>carl</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Jun 17, 2021 at 11:03 AM Ming Chin <<a href="mailto:mingchin.st@gmail.com">mingchin.st@gmail.com</a>> wrote:<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 dir="ltr">Hello Even,<div>thank you for your input.</div><div>I will review the raster API as you have suggested. However, as I understand the requirements of my task, I need to support the vector API as well, because we do need to support vector layers.</div><div>Can you, or anyone else here, point to a recommended guide/tutorial to implementing gdal wms vector layers (in c++)?</div><div><br></div><div>Thank you,</div><div>Ming</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 17 Jun 2021 at 08:47, Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank">even.rouault@spatialys.com</a>> wrote:<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>Ming,</p>
<p>A OGRLayer is a *vector* layer, not a raster one. So you should
rather look at the raster API:
<a href="https://gdal.org/tutorials/raster_api_tut.html" target="_blank">https://gdal.org/tutorials/raster_api_tut.html</a></p>
<p>Depending on the kind of URL you provide to GDAL, you may get
directly a workable dataset, or just a placeholder that links to
real datasets with the subdataset (which can be seen as a king of
raster layer) mechanism, using
GDALDataset::GetMetadata("SUBDATASETS") to get the list of
subdatasets, and then pass to GDALOpen() the value of one of the
SUBDATASET_xx_NAME item<br>
</p>
<p>Even<br>
</p>
<div>Le 17/06/2021 à 17:41, Ming Chin a
écrit :<br>
</div>
<blockquote type="cite">
<div dir="ltr"><br>
<div>Hello GDAL devs,</div>
<div><br>
</div>
<div>I am a GDAL rookie, and I am trying to add WMS support to
an existing GDAL (2.2.4) implementation.</div>
<div><br>
</div>
<div>I saw in this example:</div>
<div><br>
</div>
<div><a href="https://gis.stackexchange.com/questions/67416/using-gdal-to-connect-to-a-wfs" target="_blank">https://gis.stackexchange.com/questions/67416/using-gdal-to-connect-to-a-wfs</a></div>
<div><br>
</div>
<div>that its possible to provide <span>OGRSFDriverRegistrar::</span><span>Open(sURL, </span><span> FALSE
);</span></div>
<div><span><br>
</span></div>
<div><span>with a url and use it to open an OGRDataSource.</span></div>
<div><span><br>
</span></div>
<div>And in other examples I see that <span>OGRSFDriverRegistrar::</span><span>Open() has been deprecated and
that GDALOpen() should be used instead.</span></div>
<div><span><br>
</span></div>
<div><span>So I did that, adding
cURL to our GDAL build, and then in my implementation, I
provided GDALOpen() with a URL like this:</span></div>
<div><span><br>
</span></div>
<div><span>GDALDataset *pDataset
= (GDALDataset*)::GDALOpen(sURL, GA_ReadOnly);<br>
</span></div>
<div><span>if( pDataset )</span></div>
<div><span>{</span></div>
<div><span> int nLayers =
pDataset->GetLayerCount();</span></div>
<div><span> OGRLayer *pLayer =
pDataset->GetLayerByName(sLayerName);</span></div>
<div><span>}</span></div>
<div><span><br>
</span></div>
<div><span>This seems to partially
work, in the sense that the
GDALOpen function returns a non-NULL pointer to a
GDALDataset, but when I try to call the member functions of
the resulting GDALDataset, everything seems to return zeros
or nulls;</span></div>
<div><span><br>
</span></div>
<div>The above call returns nLayers = 0, and
pLayer=NULL</div>
<div><br>
</div>
<div>but if I feed the same sURL into my web browser (Chrome),
the browser receives a properly formatted xml file that
clearly has <Layer>(s) defined in it.</div>
<div><br>
</div>
<div>What am I missing? Why am I unable to retrieve useful data
from the dataset?</div>
<div><br>
</div>
<div>Ming</div>
<div><br>
</div>
</div>
<br>
<fieldset></fieldset>
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</blockquote>
<pre cols="72">--
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My software is free, but my time generally not.</pre>
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