WMS:Linear Interpolation: Difference between revisions

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If the linear interpolation scheme is selected, the [[WMS:Scatter Point Module|2D scatter points]] are first triangulated to form a temporary TIN. The TIN is a network of triangles  connecting the scatter points together. It is used to interpolate from the  scatter points to another object such as a grid or a mesh.
If the linear interpolation scheme is selected, the [[WMS:2D Scatter Point Module|2D scatter points]] are first triangulated to form a temporary TIN. The TIN is a network of triangles  connecting the scatter points together. It is used to interpolate from the  scatter points to another object such as a grid or a mesh.


The equation of the plane defined by the three vertices of a triangle is as  follows:
The equation of the plane defined by the three vertices of a triangle is as  follows:


[[Image:linear_eq1.jpg]]
:<math>Ax + By + Cz +D = 0_{}^{} </math>


where A, B, and C, and D are computed from the coordinates of the three  vertices (x1,y1,z1), (x2,y2,z2), & (x3,y3,z3):
where <math>A</math>, <math>B</math>, <math>C</math>, and <math>D</math> are computed from the coordinates of the three  vertices <math>(x1,y1,z1)</math>, <math>(x2,y2,z2)</math>, and <math>(x3,y3,z3)</math>:


[[Image:linear_eq2.jpg]]
:<math>A = y_1 (z_2 - z_3) + y_2 (z_3 - z_1) + y_3(z_1 - z_2^{}) </math>


[[Image:linear_eq3.jpg]]
:<math>B = z_1(x_2 - x_3) + z_2(x_3 - x_1) + z_3(x_1 - x_2^{}) </math>


[[Image:linear_eq4.jpg]]
:<math>C = x_1(y_2 - y_3) + x_2(y_3 - y_1) + x_3(y_1 - y_2^{})</math>


[[Image:linear_eq5.jpg]]
:<math>D = -Ax_1 - By_1 - Dz_1^{} </math>


The plane equation can also be written as:
The plane equation can also be written as:


[[Image:linear_eq6.jpg]]
:<math>z = f(x,y) = - \frac {A}{C}x - \frac {B}{C}y - \frac {D}{C} </math>


which is the form of the plane equation used to compute the elevation at any  point on the triangle.
which is the form of the plane equation used to compute the elevation at any  point on the triangle.


Since a TIN only covers the convex hull of a scatter point set, extrapolation  beyond the convex hull is not possible with the linear interpolation scheme. Any  points outside the convex hull of the scatter point set are assigned the default  extrapolation value entered at the bottom of the Interpolation Options dialog.  The figure below shows a 2D scatter point set (small red triangles) being  interpolated to a 2D grid. The green lines represent a TIN constructed from a  scatter point set. The thick blue line represents the convex hull of the data  set. No extrapolation will occur outside of this thick blue line.
Since a TIN only covers the convex hull of a scatter point set, extrapolation  beyond the convex hull is not possible with the linear interpolation scheme. Any  points outside the convex hull of the scatter point set are assigned the default  extrapolation value entered at the bottom of the ''Interpolation Options'' dialog.  The figure below shows a 2D scatter point set (small red triangles) being  interpolated to a 2D grid. The green lines represent a TIN constructed from a  scatter point set. The thick blue line represents the convex hull of the dataset. No extrapolation will occur outside of this thick blue line.


[[Image:linear01.gif|frame|none|''Convex  Hull of a Data Set'']]
[[Image:linear01.png|thumb|none|450 px|Convex  hull of a dataset]]




==Related Topics==
==Related Topics==
* [[WMS:Interpolation Options|Interpolation Options]]
* [[WMS:Interpolation Options|Interpolation Options]]
* [[WMS:Scatter Point Module|2D Scatter Point Module]]
* [[WMS:2D Scatter Point Module|2D Scatter Point Module]]




{{WMSMain}}
{{WMSMain}}
[[Category:Interpolation|L]]
[[Category:Equations]]

Latest revision as of 15:40, 29 March 2017

If the linear interpolation scheme is selected, the 2D scatter points are first triangulated to form a temporary TIN. The TIN is a network of triangles connecting the scatter points together. It is used to interpolate from the scatter points to another object such as a grid or a mesh.

The equation of the plane defined by the three vertices of a triangle is as follows:

where , , , and are computed from the coordinates of the three vertices , , and :

The plane equation can also be written as:

which is the form of the plane equation used to compute the elevation at any point on the triangle.

Since a TIN only covers the convex hull of a scatter point set, extrapolation beyond the convex hull is not possible with the linear interpolation scheme. Any points outside the convex hull of the scatter point set are assigned the default extrapolation value entered at the bottom of the Interpolation Options dialog. The figure below shows a 2D scatter point set (small red triangles) being interpolated to a 2D grid. The green lines represent a TIN constructed from a scatter point set. The thick blue line represents the convex hull of the dataset. No extrapolation will occur outside of this thick blue line.

Convex hull of a dataset


Related Topics