[GIS] How feasible to extract data from KML/KMZ files

kml

We have a large bunch of KML files, they are basically global cable maps. In our company they are wide-spread and everybody uses them with Google Earth.

Now there is an interest to extract information from these files, e.g. Cable Lengths. With Google Earth extracting Cable Length is a very tedious task because you need to look at each tiny segment's height profile. So I started writing a software to read those files, problem is: the quality of most of those KML/KMZs is really low. Sometimes linestrings contain too many or even duplicate coordinate-sequences. You can even see that in Google Earth.

So question: does it make sense to try to parse these KMLs to calculate cables' total length? Or is this too much asked from KML format?

Best Answer

You can convert kml to other GIS formats such as shape using ogr2ogr, part of gdal. If there are too many points or double points this should not really cause problems: calculating a length is a fast progress.

Although they work with any GIS program, calculating the actual length is not that straightforward: most of them only work with projected data, and if you have global cables they should work with unprojected data as well.

BTW: a google search turned up with this tool to measure lengths in kml files: http://freegeographytools.com/2007/determining-google-earth-path-lengths

Related Solutions

[GIS] How to adjust KML files so that they display properly in Google Earth, ArcGIS Desktop & ArcGIS Online

The coordinates of your bounding box seem to be at equivalent locations on "default" projected basemaps in Google Earth, ArcScene, ArcGIS Desktop, and ArcGIS Online. That makes sense based on my understanding: these projections are equivalent (EPSG:3857) and all use the WGS84 Datum (EPSG:4326).

Although we're dealing with KML ("Google") data, the coordinates are not in "Google" format -- the bounding box is plain old WGS84. Since the data was previously viewed on a 3D surface, it did not need to be projected. By default, Esri must project all data into EPSG:3857 when added to ArcGIS Online (since it must contain an Esri basemap, all projected in this system). I don't understand the Esri support response.

Perhaps it is indeed a bug or feature gap in projecting large extent KML GroundOverlay objects in ArcGIS Online as KHibma suggests. I have tested KML GroundOverlay to ArcGIS Online and it works correctly. It appears to be accurate up to +/- < 10 ft on smaller extents (tested up to ~100 x 100 miles) but have not be able to verify that KML GroundOverlay to ArcGIS Online projects accurately on large extent data(e.g., "quadrant", NE hemisphere). In the example data accuracy is around +/- 100 mile.

Maybe try breaking up your groundoverlay images into smaller extent tiles and referencing each in the KML?

[GIS] Combine KML files with Python

You can use the fastkml python lib for this. It can be found at https://fastkml.readthedocs.io/en/latest/ with all instructions to the usage.

Here is a code example for using this library to generate a kml structure.


from pathlib import Path

from fastkml import kml
from shapely.geometry import shape


def read_kml(kml_text):
    k = kml.KML()

    # Reading the kml from a text string
    k.from_string(kml_text)

    k_doc = list(k.features())[0]

    # Getting the first document child that must be a folder or a placemark
    # but you can iterate over it to get multiple folders or placemarks
    doc_child = list(k_doc.features())[0]

    lst_geoms = list()
    if isinstance(doc_child, kml.Folder):
        for feature in doc_child.features():
            lst_geoms.append(feature.geometry)
    elif isinstance(doc_child, kml.Placemark):
        lst_geoms.append(doc_child.geometry)

    # Returning the geometries found list  
    return lst_geoms


def generate_kml():
    # Final file IO
    k = kml.KML()
    ns = '{http://www.opengis.net/kml/2.2}'

    # Creating document structure
    document = kml.Document(
        ns, "SOME_IDENTIFICATION",
        "SOME_NAME", "SOME_DESCRIPTION"
    )
    k.append(document)

    # Creating folder structure
    # Note that a kml can have multiple folders
    folder = kml.Folder(
        ns, "SOME_IDENTIFICATION",
        "SOME_NAME", "SOME_DESCRIPTION"
    )
    document.append(folder)

    # Creating placemark structure
    # Note that a kml can have multiple placemarks
    placemark = kml.Placemark(
        ns, "SOME_IDENTIFICATION",
        "SOME_NAME", "SOME_DESCRIPTION"
    )
    # Passing the geometry to the placemark
    # It can be a shapely geom (Polygon, MultiPolygon, Polyline, Point, etc)
    placemark.geometry = shape("SOME_GEOJSON_GEOMETRY_HERE")

    # Adding the placemark to the previous created folder
    folder.append(placemark)

    final_kml_text = k.to_string(prettyprint=True)

    output = Path(__file__).parent / "test.kml"
    output.write_text(final_kml_text.encode("UTF-8"))


if __name__ == '__main__':
    # U can either generate a kml from a existing data
    generate_kml()
    # or read another kml to get the features and properties
    # to generate your own
    geometries = read_kml("SOME_KML_STRINGIFIED_TEXT")

Best Answer

Related Solutions

[GIS] How to adjust KML files so that they display properly in Google Earth, ArcGIS Desktop & ArcGIS Online

[GIS] Combine KML files with Python

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