[GIS] Problem using polygonize / raster to vector in QGIS

polygonizeqgis

I want to take my raster (multi ortophotos (.tiff) placed together using the "Build virtual Raster" option with the pyramids) and poligonize it. Something like this: gdal polygonize in python error, blank polygon created into an .shp file.

However, when I use the poligonize option an error appears saying that the process finished shortly after the beginning.

After having a closer look on my raster I found this:

Could this be the problem? How can I take them out of my layer?

After some research, I found the clip plugin but to use these I have to have a shapefile with the contour or something like that and I don’t have nothing. I must say I’m a new to QGIS and so to Geography 🙂

I thought about making my own contour, by drawing the boundaries, but could not found any plugin to do this. Is there a way to clean up my layer in order to pass it from raster to vector correctly? in shapefile so that I can open it, for example, in AutoCAD?

Best Answer

Thank you very much for your help.

I was trying to use SERVAL but I couldn't find any example of application. What I managed to do in order to make the black patches to dissapear was this:

Not sure if this was what you were suggestion. I tried to use the poligonized with these layer but the error message was the same.

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QGIS Polygonize Error – Troubleshooting DLL Load Failure During QGIS Polygonize

I'm not an expert in the compilation of QGIS (so will bow to greater knowledge and please treat this answer as a suggestion and not gospel), but I can think of two possible reasons for this error:

If you have a separate instalation of GDAL for a different version of Python (especially Python 3.x) you will get similar errors and GDAL will not work in QGIS until you uninstall your other version of GDAL.
You have a different version of Microsoft Visual Studio Runtime installed than the version used to compile the GDAL binaries for QGIS. I have both MSVC2008 and 2010 installed. Off-hand I can't remember what the QGIS folk used, so one of those should work. You can get the 2010 version here: http://www.microsoft.com/visualstudio/en-us/products/2010-editions/visual-basic-express and you'll find the 2008 version somewhere nearby. Simply install and then you probably will want to restart your computer.

Given that you can get even as far as you have without getting a Python version error (I get the Python error on start-up), I think the second option is more likely.

PS: BTW the latest version of QGIS is now 1.9 according to the last update I got from OSGEO4W... though the icon still says QGIS 1.8 confusingly enough.

[GIS] Exporting shapefile into PostGIS via Python script from QGIS

For the record. An example of a Python function using OGR2OGR outside QGIS of a OSGEO QGIS dist. I used in a disk walk finding 900 shape files in recursive directories and uploaded to PostGIS with no error. To simplify the code I removed some GUID table naming to avoid duplicate table names.

def upload_to_db(shpfile):
    """
    Uploades shape files to PostgreSQL with org2ogr
    :param shpfile: Shapefile to upload to database
    :return: None
    """

    dbname = 'mydb'
    schema = 'myschema'
    host = 'xx.xx.xxx.xx'
    user = 'myuser'
    password = 'mypw'
    port = '5432'

    tablename = f'{os.path.basename(shpfile)}'

    # https://gdal.org/drivers/vector/pg.html
    command = f"""SET PGCLIENTENCODING=LATIN1 && ogr2ogr -f "PostgreSQL" PG:"host={host} dbname={dbname} user={user} password={password} port={port}" "{shpfile}" -nln {schema}.{tablename} -lco geometry_name=geom -lco precision=NO -nlt promote_to_multi -a_srs epsg:25832"""

    #print(command)
    os.system(command)

Best Answer

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