Extracting Rooftop aerial imagery using Alteryx

[DMI10000]

Hi all,

I am new to working with spatial data. Still, I am trying to build a model to extract the rooftop aerial imagery of houses in Auckland (New Zealand) so I can perform image classification.  

I am having a hard time figuring out how to extract the images so I do not have to focus on the vegetation but just the rooftops.

The first link below gives an example of aerial imagery while the second link maps the aerial imagery with the outline. Now, I am interested in the jpg image of the rooftop for my classification.

link 1: https://data.linz.govt.nz/layer/95497-auckland-0075m-urban-aerial-photos-2017/

link 2: https://data.linz.govt.nz/layer/101290-nz-building-outlines/

Please any workflow or help will be appreciated. Any questions, I am happy to furnish with more clarity.

BTW, the images can all be downloaded free. For downloads above 15GB, you just need to reduce the resolution to 1/4. 

Thanks.

David

[Ben_H]

Hi @DMI10000 ,

My understanding here is that you want to use the building outlines to clip the aerial photography so you're left with just the rooftop images is that right?

If that's the case I don't think Alteryx is exactly suited to that straight out of the box, though I'm pretty sure you could do it with Python.

It would be a much simpler operation in a GIS tool like ArcGIS (or QGIS if you wanted a free alternative)

I might have misunderstood the requirement though so let me know if that's the case!

Regards,

Ben

[DMI10000]

Hi Ben,

Thanks for your reply, and you are actually spot on regarding my request. Though I have not used QGIS before nor am I familiar with GIS. I am looking to using the images to determine the roof conditions of houses using a classification method.

Please how do I proceed with either the QGIS or making sense of of it all.

Any help will really be very helpful.

Regards

David

[Ben_H · Accepted solution]

Hi @DMI10000,

You need to be looking for functions that allow you to clip rasters with vector layers. There will be lots of tutorials out there.

Something like this may help - https://www.youtube.com/watch?v=5ftv6I7G-ys

For fun, I decided to see if I could come up with an 'out of the box' workaround solution and came up with this -

You'll note that the output images have the Mapbox copyright, this is because I used the built in satellite background imagery in Alteryx.

I just took the outline polygons, created a bounding box mask and then generated the images to match the dimensions of the box.

It is actually possible to insert your own base maps using geotiff files, which I have done once before. It's not straight forward though so you may want to ask someone at Alteryx exactly how that works.

Regards,

Ben

[DMI10000]

Hi Ben,

This is excellent, and thank you heaps! Just what I have been trying to get around.

I will reach out to Alteryx for help on the base map after I have tried it out myself.

I am so grateful. Meanwhile should you please stumble on the Alteryx code or other codes on how you implemented the base map, I am more than thankful to receive your support.

Much appreciated Ben.

David

[DMI10000]

Hi Ben,

Any thoughts on improving the image quality? I can see they are blurry and may be of poor quality for classification purposes.

David

[Ben_H]

Hi @DMI10000,

The blurryness is due to me using the built in mapping I think, doesn't have the resolution of your images.

If you can get the aerial photography from the NZ website in to Alteryx as a basemap it should resolve itself. I've definitely inserted my own geotiffs as basemap before so I know it can be done. There a bit of a process involved and you had to create your own config file that drives the mapping but it's doable.

These are the config files for the base mapping, I can't quite remember where you put your Geotifs and how you get alteryx to recognise the additional ones you add but I'm sure Alteryx can advise you on that one.

The only issue I had when I did it before was the allignment of the tiles was a hair off, I think it was down to converting between different projections.

Regards,

Ben

[DMI10000]

Hi Ben,

This is definitely helpful. I want to try it out. But I know I will have more questions for you. Please if you dont mind can I continue to send you my questions.

Many thanks for all the contributions.

David

[Ben_H]

Hi @DMI10000,

You can but I'm more than likely just going to refer you back to Alteryx, as I say it's a long time since I've done the thing you need.

It would be worth investigating QGIS as you should be able to achieve exactly what you want with that tool as well.

Regards,

Ben

[DMI10000]

Hi Ben,

Thanks for all the kind help. I upgraded my Alteryx to version 2022.3.1.395 yesterday and after doing that I tried running the workflow you shared but it shows the error below "Error: Generate Maps (43): Record #311: Tool #9: Invalid Width: '.444591'; trailing text after the integer". This error came from the macro.

Any idea what may be the problem?

Please see the image attached.

Regards

David