Jump to content
RockWare Support Forum
Olafsson

Unable to compute polynomial

Recommended Posts

I´m trying to make a polynomial out of these points, as I´m trying to determine a fault location.

704218 3557171 1280

704352 3558789 1280

704121 3558511 833

703177 3556948 -220

703468 3558091 -220

703876 3559019 -220

703635 3558692 280

707047 3559531 280

703372 3556628 280

703322 3557034 480

But I always get this error:

"Error: UNABLE TO COMPUTE POLYNOMIAL

Unable to compute this particular polynomial and therefore unable to

complete initial trend-surface analysis. Possibilities;

(1) Duplicate point - make sure the "declustering" option is activated.

(2) Overfit of data - sorry, this data set can´t be used with trend-surface.

(2) Coefficient = 0 - sorry this data set can´t be used with trend surface."

What is wrong here?

Thanks,

Olafsson

Share this post


Link to post
Share on other sites

Hi Olafsson,

I was able to grid your data with both a first order polynomial and the automatic setting. The error you're getting suggests that:

1. You haven't selected the correct columns for X, Y and Z: Double check your Input Columns

2. Your points are outside of your project area: Check the Grid Dimensions setting in the Gridding Options dialog.

If neither of these solves your problem please tell us what settings you're using.

Mitch

Share this post


Link to post
Share on other sites

Hi Olafsson,

You may want to scan the datasheet to re-calculate your project dimensions. I got the same error calculating the polynomial fit with bad project dimensions. (Now I see that Mitch posted with this suggestion too.)

Also, I suggest creating an EZ-Map with your data points and display contours created with the default triangulation algorithm. It looks like point #8 has a bad X value (707047) when compared to the other values. This method will also let you check your other points, like 7 and 10.

ezmap.png

Create an EZ-Map to check the positions and values of the data points.

Thanks,

Tom B

RockWare Inc

Share this post


Link to post
Share on other sites

Thanks! I can´t believe it... I was trying to draw the X column as a Y. Triangulation managed to do it but polynomial didn´t.

I also got rid of points 7, 8 and 10 and am now able to make a 3rd order polynomial, as I wanted.

As the grid surface stretches very high and very low; what is the best method of constraining it?

I want to constrain the grid to min:-300 m and max:1300 m. I made flat grids at these heights (Flat_-300.grd and Flat_1300.grd).

In "Grid > Filter > Limit" I am able to constrain the "Fault.grd" using the "Flat_-300.grd" with "Fault_limit-300.grd" as an output.

Now the problem: If I then try to limit the "Fault_limit-300.grd" with "Flat_1300.grd" the program crashes. Limiting only the "Fault.grd" with "Flat_1300.grd" works fine, but limiting that output file with "Flat_-300.grd" results in a crash as well.

5453269218_4439d89568_b.jpg

Share this post


Link to post
Share on other sites

Constraining the grid is actually working and creating the new fault surface however the crash occurs when creating a 3D plot. I'll have to look into that but I wonder if using a Grid Range Filter would be more appropriate. Using this filter set the Replacement Values to NULL (just type NULL in the input edit).

post-7-075404900 1297957152_thumb.png

Mitch

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×