What format do you want the alphas channel in after running gdal_polygonize.py? I ask because after processing you could open the input and read just the alpha band (band 4 I assume). Here is a short script framework that might get you started.<div>
<br></div><div>Something like:</div><div>from osgeo import gdal</div><div><br></div><div>gdal.open(inpudataset, gdal.GA_ReadOnly)</div><div><br></div><div>#Create an output</div><div><div>driverFormat = "GTiff" #Any GDAL supported write format</div>
<div>driver = gdal.GetDriverByName(driverFormat)</div><div>outdataset = driver.Create(options.output, dataset.RasterXSize, dataset.RasterYSize, dataset.RasterCount)</div><div>outdataset.SetProjection(dataset.GetProjection())</div>
<div>outdataset.SetGeoTransform(dataset.GetGeoTransform())</div><div><br></div><div>inband = gdal.GetRasterBand(4) #Band counts are 1 based. I am assuming that your band 4 is alpha.</div><div><br></div><div>#Read in the gdal array</div>
<div>input_band = inband.ReadAsArray()</div><div>outdataset.GetRasterBand(1).WriteArray(input_band, 0, 0)</div><div><br></div><div>Someone with more experience might be able to tell you a method that uses CreateCopy(), but I think that it isn't possible to selectively copy bands.</div>
<div><br></div><div>Hope that that helps, </div><div>Jay</div><br><div class="gmail_quote">On Mon, Jul 25, 2011 at 8:19 PM, jt2000 <span dir="ltr"><<a href="mailto:thakkar@nexgenwireless.com">thakkar@nexgenwireless.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">I have a very large raster file with data in the alpha band. I need to<br>
vectorize it and associate band 4 data with resulting polygons.<br>
<br>
Is there anyway to preserve alpha channel data or get that data associated<br>
with vectorized file after using gdal_polygonize.py?<br>
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