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Newbie query

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tdye

Newbie query

I'm looking for an open-source application I can use to measure archaeological artifacts from digital photographs.

I need to establish landmark points, orient the artifact, and somehow extract the cartesian coordinates of the landmark points in mm, preferably as a csv file.

Is this something I can do in LibreCAD? Or, am I barking up the wrong tree?

dellus

Re: Newbie query

Wrong tree, woof. Probably.
There is no way to correct perspective distortion in LC. If you have aerial photos made with the lens axis perpendicular to the earth surface, you could import such a photo, scale it according to a known distance and rotate it. Then you can measure any other distance, or draw the outlines of objects over the photo.
You can define a point as zero and then read the relative coordinates of other points. But how to extract geographical coordinates, you need a different tool for that. CSV file, what's that?

dellus

Re: Newbie query

In reply to this post by tdye

Addendum:
If you mean coordinates as surveyors use, related to the equator and 0-meridian in distance units, you can move the contents of the drawing (and the imported photo) from some point you know those surveyor coordinates to there. This will result with the drawing carrying very large point values numerically, which might induce trouble. But you can try.

tdye

Re: Newbie query

In reply to this post by dellus

Aloha dellus,

dellus [via LibreCAD] writes:

> Wrong tree, woof. Probably.
> There is no way to correct perspective distortion in LC. If you
> have aerial
> photos made with the lens axis perpendicular to the earth
> surface, you could
> import such a photo, scale it according to a known distance and
> rotate it.
> Then you can measure any other distance, or draw the outlines of
> objects
> over the photo.
> You can define a point as zero and then read the relative
> coordinates of
> other points. But how to extract geographical coordinates, you
> need a
> different tool for that. CSV file, what's that?

Agreed. Thanks.

CSV = comma separated value, a text file format used by many
applications to exchange data.

All the best,
Tom

--
Thomas S. Dye
http://www.tsdye.com