Looking For Free Area Calc Software?!

[Sigurd]

I've seen some time limited GIS software that allows you to easily calculate image area but I haven't been able to find a free utility...

I don't think its a hideously complicated problem to solve. I'd like to be able to import a graphic file and then draw a polygon on top of it. The program has to return the area of the polygon and probably the perimeter.

Does anyone know of a free, legal, program that will do this?

It has to allow me to trace on top of a graphics file so I can outline a feature on a map (eg. lake, island, etc....)
Units of measure is not really a problem thats a simple conversion.

It would be a useful utility for a mappers bag of tricks....



Sigurd

[Redrobes]

If you know the area of the map in total or can cut out a rect of known area around the complicated bit then you can start with that. Then add a layer, trace around the part and fill it black and white and dump the original.

With the black and white version you can use a mega blur on it. The one I like in PSP is under Effects / Geometric Effects / Pixellate and do it as much as it will allow. Once the whole screen is one uniform gray color then get the color value and divide it by 255 and multiply by original area to give approx area of complicated shape. That should work to about 1% - 2% of actual accuracy due to errors in rounding.

[Sigurd]

Thanks for the process I wouldn't have thought of doing it that way.

Rectangles are the easy case. Right now thats how I calculate - draw rectangle measure height, width and multiply. Complicated shapes are too,,,, complicated. I'm lazy and I'd love something simple. Right now, its not elegant.


I'd like to be able to load the graphic file in a program and simply trace shapes. Its a common enough GIS function but I am having trouble finding a free program to do it.


Sigurd


Thanks for the suggestion though.

[Redrobes]

You can do any shape with that technique not just rects. What your doing is basically what we call a 1 bit DtoA with oversampling - digital to analogue filter and the mega blur is a huge amount of oversample. By using a mega blur that will find the average gray value for the image which is proportion of black to white ratio which is equiv to area of island to total map size. Anyway - gotta shoot off now.

[ravells]

I think drawplus might do it and I know the early versions are free downloads - let me check and come back to you. Have you looked at inkscape? That might do it too.

[Sigurd]

You can do any shape with that technique not just rects. What your doing is basically what we call a 1 bit DtoA with oversampling - digital to analogue filter and the mega blur is a huge amount of oversample. By using a mega blur that will find the average gray value for the image which is proportion of black to white ratio which is equiv to area of island to total map size. Anyway - gotta shoot off now.

Thanks Red, I understand and I'll try the process but I'd love something as simple as:

Trace shape(s)
Press button
Get area

Its sort of a fringe ability that becomes more useful the more easy it is to do.


Sigurd.

[NeonKnight]

neener, neener, neener. CC3 Does exactly what you want

Probably because it is mapping software based off a CAD program.

[Redrobes]

CC3 Free now huh ? hee hee

Seriously tho, a CAD tool or dedicated mapping app - esp a vector based one should be able to do it but its not too much of a pain to do this for any raster image and although its approximate, you might be able to get the area without any tracing which might in some cases be quite tedious - thinking of the UK coastline.

Since not everyone has CC3 and unless somebody says that there is a nice free app to do just the thing, ill do a quick tut to show how you might be able to do it. Not saying its the best way but its a way.

[NeonKnight]

No, not really free, but if it is what you use for mapping, you don;t need to port from here to there and back again to find the info, nor does one need an add-on, it's all right there.

[wacko76]

Thanks Red, I understand and I'll try the process but I'd love something as simple as:

Trace shape(s)
Press button
Get area

Its sort of a fringe ability that becomes more useful the more easy it is to do.


Sigurd.

Hi, I just registered now, specifically to answer.

I have something even simpler than "trace, press button, get area". What about "trace, get area"?

Use Paint.NET. Open your file, use the selection tools to select the area you want to measure and at the bottom PAINT.NET tells you exactly how many square pixels you have selected. All you need now is to convert that to meters or whatever.

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