Calculate path length for line and freedraw?

[JCCKwong]

Hi!

Great streamlit component! I want to calculate the path length (ie: total distance in pixels) for the freedraw and line tool. For the line tool, it's pretty straightforward by applying the Pythagorean theorem using the width and height provided. But I'm having a little trouble figuring out the best/most efficient way to do this for the freedraw tool.

Any advice for be greatly appreciated. Thanks!

Jethro

[andfanilo]

Hey @JCCKwong !

That's a super interesting question, let me dig into it. It seems there are some Python SVG libs that could help:

• https://github.com/regebro/svg.path
• https://github.com/mathandy/svgpathtools

Let me check and come back to you (and you find before me, hope to read your solution!)

Fanilo

[andfanilo]

So it is absolutely possible with svgpathtools.

I've added the code to the demo, here's the snippet I used:

from streamlit_drawable_canvas import st_canvas
from svgpathtools import parse_path

canvas_result = st_canvas(...)

if (
    canvas_result.json_data is not None
    and len(canvas_result.json_data["objects"]) != 0
):
    df = pd.json_normalize(canvas_result.json_data["objects"])
    paths = df["path"].tolist()  # get list of paths from dataframe
    for ind, path in enumerate(paths):  
        path = parse_path(" ".join([str(e) for line in path for e in line]))  # concat each path into its SVG string representation and parse it
        st.write(f"Path {ind} has length {path.length():.3f} pixels")

[JCCKwong]

This is perfect! Many thanks to you and the Streamlit team for making it so easy to develop these high quality apps. Looking forward to sharing my next clinical app in the future!

[JCCKwong]

Hi @andfanilo , sorry to revisit this issue.

I implemented the code described above.

if (canvas_result.json_data is not None and len(canvas_result.json_data["objects"]) != 0 ):
     st.dataframe(pd.json_normalize(canvas_result.json_data["objects"]))
     df = pd.json_normalize(canvas_result.json_data["objects"])
     paths = df["path"].tolist()

     for _, path in enumerate(paths):
         path2 = parse_path(" ".join([str(e) for line in path for e in line]))
         st.write(path2.length())
         direct_dist = math.sqrt((df["width"][0]) ** 2 + (df["height"][0]) ** 2)
         tort = path2.length() / direct_dist
         st.write("Tortuosity: ", tort)

However, I get a TypeError. Any advice would be amazing!

[andfanilo]

Hmmm that's odd, can try to add a st.write(path) to check the value and see if it's a nested list or another type of object?