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2-Guest

## Getting values from a log-log graph in mathcad 15

Dear all,

in a design code a log-log graph is given from wich a value must be read using the known value of X.

Now I have two issues:

- how to convert this drawn graph into something mathcad can work with? Getting values from a log-log graph by hand is inaccurate, so I want to use as little hand-picked values as possible to get mathcad to work with. My idea is to make a table of X and Y values and let mathcad determine a formula for this and plot this in a graph to see if it looks like/fits the graph in the design code. But how to do this?

- Secondly mathcad needs to use this info/graph to determine the value of Y from this graph. How can this best be done?

2 REPLIES 2
23-Emerald I
(To:corne_mo)

There were a number of posts that described importing an image file (Mathcad reads as a matrix) and digitising it; but those were all in Mathcad 15 or before.

For this type of task I reach for the freeware program "Tracer."  It allows you to import am image, scale it, and extract point pairs into a table.  (Tracer will only do linear scaling; so you need to use exponents of ten when you scale the image (0 is 1, 100 is 2, etc., the raise it back to the power after you've imported the points.)

After you get your table of points there are a number of curve fitting possibilities.  Once you have a function definition in Mathcad, determining y for a given x is simply evaluating your function.

16-Pearl
(To:corne_mo)

Hello,

here is a small routine that might help. I didn't bother to convert log-log data, so I did it only on normal data. The data you have to enter manually I'm afraid. 😉

Raiko

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