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Creating Shapefile layer automatically using from Raster Layer Image- QGIS


Sudhendu Pandey 3

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Firstly, excellent videos with Dr. Spotfire Session. Thank you!

I have been following this video: https://www.youtube.com/watchv=Oe_PZi42a_k(Dr Spotfire- QGIS & Shapefiles in Spotfire)

I was wondering if there is any automatic way of using an image as a raster layer and then creating polygon shapes over it I know there is one way to do it where I keep drawing individual shapes, which is OK for smaller base raster layer, but in my case, I have 100 + shops and departments in the base layer. And they are of different shapes:square, rectangle, circle and polygonal.

Is there any way I can get QGIS (or any tool for that matter) to identify using the image different shapes (the borders are very visible) and create the shape for me The image has clear border, all I want is shape layer above it.

Thanks,

Sudh

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Hello Sudh,

It might be possible to digitize your raster image to a vector and then export it as a Shapefile for use in Spotfire. Using the following method:

1. You need to georeference the image

Your image has no spatial reference. You can load it into QGIS but it won't know where to put it. In order to tell QGIS where it belongs in space you have to provide geographic reference points.

This process is described here:http://www.qgistutorials.com/en/docs/3/georeferencing_basics.html

2. You need to digitize the image

Once the image is georeferenced, you have to convert it to vectorusing the vector creation tools.

This process is described here:http://www.qgistutorials.com/en/docs/digitizing_basics.html

3. Export to Shapefile and import in Spotfire

Note that digitizing an image is not perfect science and can lead to approximations. Expect the digitized map to now look exactly as the source raster image.

I hope this will help you.

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Thanks Arnaud for the detailed answer!! Let me try the above methods. But for now, I found an option within QGIS to automatically convert an raster image to shapefile (can't remember the name of  the option...) . It is not perfect , but just works fine for my purpose. 

 

Thank you again! Sudh

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