Extending a Surface

[Joyfer]

I would like to extend a surface to a outer boundary. When I use kriging to do this my surface becomes too inaccurate, the attached picture shows what kriging does to the surface. In the picture notice the elevations of the surface, you can tell where the survey points are because they are lower than the surface around it. All I need to do is extend the outer points to a boundary and leave the rest of the surface alone, any suggestions?

[sboon]

How are you applying the Kriging operation?  I've generally found that in order to extend a surface it's best to select a source group of TIN points within a polygon that borders on, and surrounds the area to be added.  The area that I use for the new grid of TIN points is usually another polygon with a gap left between it and the existing TIN.  The effect on the existing TIN is minimized this way.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[Joyfer]

Question about what you mean by, "it's best to select a source group of TIN points within a polygon that borders on, and surrounds the area to be added"?

Are you saying to select points by selecting a polygon boundary that surrounds the boundary of the output region? I get the same results as before, which makes since because either way the same points are selected.

The way I am kriging is...

1) I select the points (which would be all the points in the existing surface)

2) I select output region (which is a surrounding polygon larger than the existing boarder of the surface)

Am I missing something you said?

Thanks again!

[sboon]

If your output region overlaps the existing surface then the grid of new points you're creating will change the existing TIN.  In this case your output region should be a donut shape that wraps around the outside.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[Joyfer]

Alright, if you look at the attached picture. What I did this time was added only the points that are inside the green doughnut shaped polyline. After extending the surface to the red polyline you still see the effect on the whole surface.

[sboon · Accepted solution]

The first attached image shows the original TIN and the polyline that I used to define the output region in the dialog.  Note that it surrounds but doesn't touch any of the original.  The second screenshot shows the result.

Steve
Please use the Accept as Solution or Kudo buttons when appropriate

[Joyfer]

Yay, I understand now! Thank you so much for hanging in.