Efficient methods for extracting data from line graphs in images, especially for larger datasets - Looking for a drag-and-drop solution

[bigjohn]

I need to extract data from line graphs in images, and I've been using an overlay method that requires manually adjusting each (x,y) point until it aligns with the corresponding point in the image. However, this is a time-consuming process, especially for larger datasets - my current graph has 180 points. I'm wondering if there are more efficient methods for extracting data from line graphs in images, especially for larger datasets. I'm also looking for a drag-and-drop solution to make the process easier. Does anyone have any suggestions or tips on how to accomplish this? Any input would be greatly appreciated. Thank you!

 

[Hui]

BigJohn

This is something I've wanted for ever, and for some reason your post inspired me to tackle it.

What I did using step by step below works a treat as shown here !


The Excel file is attached!

What did I do

I used QGis a GIS Package
I setup a new project using a GDA94 Spheroid
I imported the image and Georeferenced it
ie: gave it 0,0 to 500,40 coordinates
But Because QGis works on a spheroid I used a West Australian coordinate system and added 750,000 to the eastings and 7,300,000 to the Northings as I georefrenced the image of the chart

I then added new lines and digitized each string in real world coordinates, zooming in as I went to get it as accurate as possible


I then converted the strings to points and added Geometry Attributes to the file
I finally saved it as a CSV File,
I opened it in excel
and subtracted the 750,000 and 7,300,000 values from the X & Y Values
I separated the two lines and made a chart
Voila

Now I am a very experienced QGis user and so this all took about 5 minutes

If there is enough interest I may even write a Post in detail about how to do that?

Enjoy

 

[bigjohn]

Hi Hui,

Thank you so much. I find it very accurate with all the high and low point to the point. I would very much appreciated if you post on how to do this. I have more chart to do work with.