I need to overlay two images and compare relationship

M
Posted By
mcgrath
Feb 9, 2006
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2563
Replies
6
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Closed
I have two scanned images (usually tif images)of maps at different linear scales; a flood map (typically 1"=2000′) and a parcel map of differing scales. What I want to do is overlay them and adjust one image up or down proportionatly to match the other image. Both images have section lines that will make it easy to align.

More than likely the flood map would be made transparent to look like a watermark over the parcel map. I have to do this operation some days 20-30 times and waste TONS of paper at a copier resizing one of the maps a few times, then using a light table draw the parcel lines over the flood image.

I am serious, if I could find a program to do this, I would typically save a ream of copy paper a week minimum (and copier toner to boot!).

Please help!, Thanks
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A
Avery
Feb 9, 2006
On 9 Feb 2006 04:18:14 -0800, wrote:

I have two scanned images (usually tif images)of maps at different linear scales; a flood map (typically 1"=2000′) and a parcel map of differing scales. What I want to do is overlay them and adjust one image up or down proportionatly to match the other image. Both images have section lines that will make it easy to align.

More than likely the flood map would be made transparent to look like a watermark over the parcel map. I have to do this operation some days 20-30 times and waste TONS of paper at a copier resizing one of the maps a few times, then using a light table draw the parcel lines over the flood image.

I am serious, if I could find a program to do this, I would typically save a ream of copy paper a week minimum (and copier toner to boot!).
Please help!, Thanks

Maybe I don’t understand the complexity of this, but it sounds fairly easy.

Open both images in PS. Drag a copy of the flood map over the parcel map. You will now have two layers in the parcel map image. Adjust the transparency of the flood map layer to say 50% -experiment here. Go to Edit>Transform> Scale and pull the flood map layer around until it fits.

I don’t know how linear the transform will be or how accurate the requirement, but it has to be better than your current method and could not take more than a few minutes.

There may well be better, more accurate ways to do this. i am sure someone will know.
M
mcgrath
Feb 9, 2006
Thanks for the good start- Actually I am hoping to keep it simple…

It would be tha same as placing two images on a light table and aligning the edges to see their relationship to each other (i.e. "Which parcels does the wash / creek run through?")

The trick is getting both images to the same scale, thus the reams of wasted paper. In most cases I am not so concerned what the final scale is, more concerned that the images overlay the same total area. Both images have an outline (square or rectangle section lines) that represent the exact same amount of area.
JF
John Forest
Feb 9, 2006
If the outline covers the exact same area you could use the measure tool to check the sizes of the outline in each map and then a little arithmetic would let you calculate the percentage you have to enlarge (or shrink) one to fit the other.
ND
Norm Dresner
Feb 9, 2006
"John Forest" wrote in message
If the outline covers the exact same area you could use the measure tool to check the sizes of the outline in each map and then a little arithmetic would let you calculate the percentage you have to enlarge (or shrink) one to fit the other.
PS, like most programs, only does shrinking and expanding in integer units. Some programs do it in integer percentages, some in limited precision entry (or evaluation) for entered sizes. You may not be able to get the two maps to align perfectly. A difference of a fraction of a percent might not matter to you here, though.

If you do need to have a precise alignment, there are standalone programs that will do the job — some even letting you enter different scales for the horizontal and vertical directions.

Norm
N
noone
Feb 9, 2006
In article ,
says…
I have two scanned images (usually tif images)of maps at different linear scales; a flood map (typically 1"=2000′) and a parcel map of differing scales. What I want to do is overlay them and adjust one image up or down proportionatly to match the other image. Both images have section lines that will make it easy to align.

More than likely the flood map would be made transparent to look like a watermark over the parcel map. I have to do this operation some days 20-30 times and waste TONS of paper at a copier resizing one of the maps a few times, then using a light table draw the parcel lines over the flood image.

I am serious, if I could find a program to do this, I would typically save a ream of copy paper a week minimum (and copier toner to boot!).
Please help!, Thanks

If I understand what you wish to do (civil engineering background, but NOT cartography, so correct me, if I’m wrong), you have two maps in different scales. Each map has section lines that are identical, just in different scales. Open the "parcel map" in PS. As others have said, Open the "flood map," Make a Selection (could be Ctrl-A [Select All], or use the Marquee to refine the Selection), Ctrl-c (Copy), make parcel map active, and Ctrl-p ( Paste). As stated before, adjust Opacity of flood map, so you can see what you’re doing. Find an intersection of the section lines, that is within the area that you wish to work. Use the Move Tool, to position that intersection (on flood map) to align with that same intersection on the parcel map. Zoom in, to get the alignment perfect. Now, you may need to Zoom Out to get the edges of the image visible – I’d then expand the canvas view, so I can see the "handles" in the next step. With the new Layer (flood map) active, choose Edit>Transform>Scale. You will get a rectangle "bounding box" with "handles"
visible, but also, what looks like a printer’s target (circle with cross- hairs) in the middle of the bounding box. Move it to the intersection point, that you have aligned to, say upper right. Then while holding Shift, click- drag on the opposite corner handle (in this example, lower right) and re-size your flood map Layer. You should see the section lines line up between the two Layers, flood map upper and partially transparent, and the parcel map below, at 100% Opacity. When the section lines match, hit Enter. I’d play with the Opacity setting for the upper Layer, and watch to make sure that the section lines DO match up. If satisfied, Save_As PSD, so you can always go back. If they do not match, you can always Ctrl-z and start over.

Hope this is what you need to do, and that it helps.

Hunt
MR
Mike Russell
Feb 9, 2006
wrote in message
I have two scanned images (usually tif images)of maps at different linear scales; a flood map (typically 1"=2000′) and a parcel map of differing scales. What I want to do is overlay them and adjust one image up or down proportionatly to match the other image. Both images have section lines that will make it easy to align.
….
Avery and Hunt have given good answers re resizing a transparent layer. Download the 30 day trial version from www.adobe.com and verify that the procedure works for you.
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Mike Russell
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