Photo: Straightening Blueprints

[JimSlade]

I have a lot of scanned blueprints. These frequently have equally spaced vertical and horizontal lines. During the blueprint, scanning, or microfilm process these lines end up deviating such that the vertical and horizontal lines are not perpendicular.

Is there any simple way in Photo transform an image with a grid of lines into an image where the grid is perpendicular and equally spaced?

[pixelstuff]

I think what you are wanting is the Perspective Tool in the left side tool bar.

[NotMyFault]

The effort depends. In easy cases like a global distortion a simple perspective filter may do the job 

In case you have multiple local distortions it becomes very tedious, a mesh warp filter can do the job but requires hours per image for fine tuning.

[GarryP]

If the blueprints have been scanned with something like a flat-bed scanner, from flat drawings – i.e. the scans are ‘flat’ with no 'z-axis distortions' – then it’s possible that the only thing that is needed is to use the Straighten functionality of the Crop Tool .

[David in Яuislip]

Original mesh, skewed and rotated

Fix the rotation with the crop tool as GarryP says
Switch the grid on and unskew the vertical lines with S in the transform panel

[JimSlade]

How do I enable the transform panel? It's visible but everything disabled.

Her is an example of what I have.

The horizontal lines are not at right angles to the vertical lines.

[pixelstuff]

27 minutes ago, JimSlade said:

How do I enable the transform panel? It's visible but everything disabled.

Her is an example of what I have.

The horizontal lines are not at right angles to the vertical lines.

Those look like they are perpendicular to me. When I drop it into Affinity Photo and pull guides out they follow along perfectly.

EDIT: Wait, I zoomed in closer and see what you are talking about. The perspective tool should work fine for fixing it.

You can see in the upper right corner how far I shifted the right side down, leaving a transparent area.

[firstdefence]

Select the Move tool 'V' on the keyboard, then select image layer and the transform options should become active.

@pixelstuff doesn't the perspective tool distort the original design so that its no longer an accurate facsimile of the scanned document.

[pixelstuff]

13 minutes ago, firstdefence said:

Select the Move tool 'V' on the keyboard, then select image layer and the transform options should become active.

@pixelstuff doesn't the perspective tool distort the original design so that its no longer an accurate facsimile of the scanned document.

It seems to me that is exactly what you want. You already have a distorted scan, you are wanting to reverse distort it basically.

[firstdefence]

8 hours ago, pixelstuff said:

It seems to me that is exactly what you want. You already have a distorted scan, you are wanting to reverse distort it basically.

I’m not the original poster @JimSlade is. I suppose the question is, does it matter that the blueprints; being distorted when scanned will not be accurate when the scan adjusted in Affinity Photo unless Jim uses a grid set to the correct proportions of the original blueprint. 
 

how accurate does this need to be?

[Alfred]

9 hours ago, firstdefence said:

so that its no longer an accurate facsimile

 

47 minutes ago, firstdefence said:

how accurate does this need to be?

If it’s not accurate then it’s not a facsimile! But it was you, not @JimSlade, who mentioned that term.

[firstdefence]

@Alfred Pixelstuff wrote as if I was the OP I was simply pointing out I was not the OP.

I know I used the term, I wasn't saying Pixelstuff said it, but I'm still waiting for an answer as to the accuracy requirements, I think all of that should be dealt with at the scan stage so no correction is required.

[JimSlade]

Thanks much for the help..

 

It needs to be as accurate as possible within the bounds that one can reasonably do.  it would be great to have all the grid lines parallel or perpendicular.