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Unferenced local system to UTM

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    Leslie McWhirter

    Hello crhansen,

    Surfer is not converting from the unreferenced system to UTM NAD83, what it's doing is associating the coordinates in your x,y,z data file with that system. So the axes won't change, but now you will be able to convert the map to another system.

    Think of coordinate conversions in Surfer like a language translation from Chinese to English using Google Translate. When you create the map and it's unrefreenced, this is like copy/pasting the text into Google Translate. It doesn't know what this text is in now or what you want it in, but the text is there. Then when you set the coordinate system of the map layer, this is like setting the language that the copy/pasted text is in (Chinese). This doesn't change the axes or the map, just like it doesn't change the text in Google Translate. Finally, once it knows that initial info, you can change the coordinate system of the map frame to anything you want. This is akin to setting the language you want the text displayed in (English). Now the map (or text in Google Translate) is changed to display in the system you specified.

    Does this make sense?

    Thanks!

    Leslie

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    Sabrina Pearson

    Hi Colin,

    When the two coordinate systems are known, lesson 14 about changing the projection is actually converting between the two systems. You can see the new coordinates in that lesson in columns D and E. If you compare those with other maps that you know are in WGS84 in the same area, the coordinates would match. The program truly is changing those coordinates.

    When you assign coordinates to a previously unknown layer or data set, you are telling Surfer that despite whatever the values are and however right/wrong they may be, Surfer is to consider the data in the coordinate system that it is being told. So, you could have data in the 0-100 range and tell Surfer that it is in UTM NAD83. Even though the values don't make sense (to us) in that range in that system, Surfer will treat the data as if it were in that system. If you try to overlay it with maps that ARE in that system, the data won't match unless it really were in the system.

    This ability to assign the system is most useful if you know the data really is in a system and you want to be able to convert it to something else. I would not recommend using it if the original data is in an unknown arbitrary system. Now, if you can add/subtract values from your arbitrary local system to move it to UTM or State Plane, you could do that mathematical offset and assign the system.

    For instance, in your project area, if you know that (0,0) is your lower left corner and your coordinates are in meters. And, you also know that same point is (588000,4180000) in UTM meters. In the worksheet, you could add 588000 to all the X values and 4180000 to all the Y values. Your arbitrary system is now UTM meters. You can assign the system to these new values. You can then use the steps from lesson 14 to convert the UTM meters to NAD83.

    I hope this helps!

    Thanks,

    Sabrina

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    crhansen
    Your response is somewhat helpful. I guess I was thinking more of the case where you actually want to convert from one coordinate system to another, which is well described in Lesson 14 on pages 120-122 of the Surfer v13 user manual. The point is that the conversion can only take place when the original coordinate system is known. Your analogy of the language translation is interesting but I am still having a hard time seeing how you can change the display from one coordinate system to another, without actually changing the projection, as in Lesson 14 noted above. Maybe the "mud" will clear off my eyes as I get to know Surfer better. I like what it can do so far. Best Regards, Colin, Calgary, Alberta
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