0

Is it possible to create a LineString object with Python's osgeo/ogr library starting from multiple Point objects?

For example, I know from the Python GDAL/OGR Cookbook that I can create a MultiLineString by adding multiple LineString objects:

from osgeo import ogr multiline = ogr.Geometry(ogr.wkbMultiLineString) line1 = ogr.Geometry(ogr.wkbLineString) line1.AddPoint_2D(1214242.4174581182, 617041.9717021306) line1.AddPoint_2D(1234593.142744733, 629529.9167643716) multiline.AddGeometry(line1) line2 = ogr.Geometry(ogr.wkbLineString) line2.AddPoint_2D(1184641.3624957693, 626754.8178616514) line2.AddPoint_2D(1219792.6152635587, 606866.6090588232) multiline.AddGeometry(line2) print(multiline.ExportToWkt())

However, when I use this idea to create a LineString from multiple Point geometries, it doesn't work:

from osgeo import ogr coords_p1 = [1214242.4174581182, 617041.9717021306] coords_p2 = [1234593.1427447330, 629529.9167643716] pt1 = ogr.Geometry(ogr.wkbPoint) pt1.AddPoint_2D(*coords_p1) pt2 = ogr.Geometry(ogr.wkbPoint) pt2.AddPoint_2D(*coords_p2) line = ogr.Geometry(ogr.wkbLineString) line.AddGeometry(pt1) line.AddGeometry(pt2)

When I try to run the snippet above, it gives me the following error:

Traceback (most recent call last):

File "C:\Users\diasf\AppData\Local\Temp/ipykernel_43960/3403084045.py", line 11, in

line.AddGeometry(pt1)

File "C:\ProgramData\Anaconda3\envs\myenv\lib\site-packages\osgeo\ogr.py", line 6245, in AddGeometry

return _ogr.Geometry_AddGeometry(self, *args)

RuntimeError: OGR Error: Unsupported geometry type

I know the snippet above would work if I used line.AddPoint(*coords_p1) instead of line.AddGeometry(pt1) (i.e., it works if I pass each point's coordinates to the LineString object instead of trying to add the actual Point geometries).

But is there a way to build LineStrings out of Point geometries, or is this just not possible?

Improve this question
6
  • You're doing exactly that in the first example using line.AddPoint(). It looks to be failing because you're trying to use line.AddGeometry() instead in the second example Commented Oct 14, 2021 at 16:42
  • Well, that's the whole point of the question (pun marginally intended =P). I don't want to pass the coordinates of the points to the LineString object. I want to, instead, pass the Point geometries themselves. Note how in the first example, there is a statement that says multiline.AddGeometry(line2). Here, I am adding a LineString geometry to another MultiLineString object. I want to know if it is possible to do something analogous, but adding Point geometries to a LineString geometry. Sorry if I wasn't very clear in my original question. Commented Oct 14, 2021 at 20:39
  • I should also mention that, in the second example, I tried two different approaches: line.AddGeometry(pt1) and line.AddPoint(pt1). Sadly, both failed. Commented Oct 14, 2021 at 20:40
  • 1
    Ah I see, sorry I glossed over that detail. I'm not aware of a way short of unpacking the coords, as you're aiming to avoid. AddGeometry() only seems to be meant for use on geoms of type wkbGeometryCollection. But you could at least unpack them from the point objects themselves if you don't have access to the original coords, with line.AddPoint(*pt1.GetPoint()) or whatever Commented Oct 14, 2021 at 22:25
  • You may have reasons for sticking with GDAL/OGR, but consider using shapely for a more Pythonic interface if not Commented Oct 14, 2021 at 22:26

1 Answer 1

Reset to default
0

As pointed out by @mikewatt, it seems like I cannot add a point geometry directly. The best I can do is use the GetPoint or GetPoint_2D methods and pass the Point geometry's coordinates to the LineString geometry, as shown below:

from osgeo import ogr coords_p1 = [1214242.4174581182, 617041.9717021306] coords_p2 = [1234593.1427447330, 629529.9167643716] pt1 = ogr.Geometry(ogr.wkbPoint) pt1.AddPoint_2D(*coords_p1) print(pt1.ExportToWkt()) #POINT (1214242.41745812 617041.971702131) pt2 = ogr.Geometry(ogr.wkbPoint) pt2.AddPoint_2D(*coords_p2) print(pt2.ExportToWkt()) #POINT (1234593.14274473 629529.916764372) line = ogr.Geometry(ogr.wkbLineString) line.AddPoint_2D(*pt1.GetPoint_2D()) line.AddPoint_2D(*pt2.GetPoint_2D()) print(line.ExportToIsoWkt()) # LINESTRING (1214242.41745812 617041.971702131,1234593.14274473 629529.916764372)
Improve this answer

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.