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View Full Version : Ridiculously odd question: Measuring Area



Xeviat
02-07-2009, 08:30 AM
Alright, I have a nearly finished map, and now I need to measure the area (in square miles) of certain regions. I have a scale, and I even know how many square miles each pixel is on my map (about 17 square miles), but I can't find a tool in photoshop to give me a pixel count.

Does anyone know of a trick to measure areas in irregular shapes?

Thanks. Here's my country shape, with a scale (in miles) if anyone thinks they can offer advice. I'll probably have to cut triangles out of it since I know how to measure the area of triangles. Being a little off won't be that big of a deal.

Steel General
02-07-2009, 08:47 AM
In Photoshop IMAGE > IMAGE SIZE will give you the total # of pixels for the entire image, I don't know how (if it's even possible) to get the # of pixels in a selected area.

Redrobes
02-07-2009, 09:01 AM
it come up before :-

http://www.cartographersguild.com/showthread.php?t=2279

read to the bottom as the process gets easier and easier as we worked out better ways to do it. If you using Gimp then Rob wrote a script to do it - as he always does ;)

Sigurd
02-07-2009, 11:52 AM
I don't think its ridiculously odd, I think its keen and insightful and shows a brilliant mind and attention to detail - I asked the same question last June...

The cheap and cheerful way is to download a copy of paint.net. This is actually a very flexible free graphic editor, but for this you want its selection tool. Open your image in the program select the area and look at the lower left corner of the screen --- # of square pixels.
You can select for contiguous areas or draw with a lasso type tool.

http://www.getpaint.net/

Other solutions exist but mostly cost money. The downside, I think, is that pixels are wider than they are tall some other methods report different area.

Autocad has an area calculator that seems to consistently report bigger numbers.
Creative Cartographer (another cad based app) also has an area calculator.
Gimp and Photoshop both give you information in their Histogram window that can help you calculate # of pixels - best refer to link....

http://www.cartographersguild.com/showthread.php?t=2279&page=2

Finally for a nuts and bolts example here is a thread on the Harn site Lythia.com that has people solving the problem with Autocad.

http://www.lythia.com/forum/viewtopic.php?f=9&t=10067

RobA
02-07-2009, 03:12 PM
it come up before :-

http://www.cartographersguild.com/showthread.php?t=2279

read to the bottom as the process gets easier and easier as we worked out better ways to do it. If you using Gimp then Rob wrote a script to do it - as he always does ;)

Sorry RR - I can't take the credit for that one ;)

Isomage cobbled together the gimp script that can calculate the area and perimeter of a selection:

http://www.cartographersguild.com/showthread.php?t=3681

-Rob A>

Redrobes
02-07-2009, 03:15 PM
Oh yes sorry Isomage

Rob, your reputation as 'the scriptmeister' was preceding you there. We have about 3 or 4 Gimp scripters now then - which is very cool.

Steel General
02-07-2009, 03:19 PM
This may have been covered in the post from a few months ago, but I figured I'd post it anyway...

If you use the magic wand tool in PS and then click on the histogram tab, it will display the total number of pixels in the selected area.

Xeviat
02-08-2009, 02:41 AM
Awesome. Thanks everyone for the replys. The Histogram trick will be what I'll use.

Rik
02-12-2009, 01:25 PM
Excellent. Now, if someone could come up with an easy way of calculating continent-size areas on a globe ...

valadaar
02-12-2009, 01:49 PM
Get a scale that can measure very precisely. Print out map. Cut out area in question. Weigh.
Cut out a square of measured size out of same paper and weigh.

Do the math :P

RobA
02-12-2009, 02:00 PM
Excellent. Now, if someone could come up with an easy way of calculating continent-size areas on a globe ...

How do you get a globe into your computer? :P

-Rob A>

waldronate
02-12-2009, 04:24 PM
Excellent. Now, if someone could come up with an easy way of calculating continent-size areas on a globe ...

If it's a real globe - take a picture of the globe using a telecentric lens, reproject the picture area from Orthographic to any equal-area projection and measure area as described above. If you're using a regular lens on a camera then use a perspective Orthographic projection (the exact name escapes me at the moment) as the source and proceed as above.

If it's already digital, reproject directly to an equal-area projection and measure pixels as above.

Rik
02-13-2009, 11:32 AM
How do you get a globe into your computer? :P

-Rob A>

It's all HandsomeRob's fault ...


If it's a real globe - take a picture of the globe using a telecentric lens, reproject the picture area from Orthographic to any equal-area projection and measure area as described above. If you're using a regular lens on a camera then use a perspective Orthographic projection (the exact name escapes me at the moment) as the source and proceed as above.

If it's already digital, reproject directly to an equal-area projection and measure pixels as above.

All good ideas. Wish I had thought of them before I started counting pixels :mrgreen:

su_liam
02-14-2009, 11:45 AM
You know, I'll betcha Waldronate's idea would probably work for my problem of converting icomaps to a reprojectible form. Next time I'm not in a time crunch, I'll have to try that.

Funny. "Waldronate," "icomap," and "reprojectable," are underlined as misspellings, but, "betcha," is hunky-dory. As is, "hunky-dory.":shock::);)

Ascension
02-14-2009, 01:55 PM
Heh :) Now that's funny...I don't even look for the red line anymore cuz just about every word of mine is underlined.

Steel General
02-14-2009, 04:22 PM
I noticed a little while ago that it doesn't like contractions, I added "didn't" to the dictionary a while ago, and just now I had to add "doesn't". :D