Feature request: Trend surface analysis report could include actual equation

[hemicidaris]

Currently the trend surface analysis report looks like this:

HTML snippet

Polynomial Order: 2

R-sqr: 0.83002

Pre-calculation Transformation Coefficients

ΔX	ΔY	ΔZ
1677454.5842407143	5658853.240481653	16.44099998474121

z = b₁ + b₂y + b₃y² + b₄x + b₅xy + b₆x²

Regression Coefficients

Coefficient Num.	Value
b1	233.745098195725
b2	-0.025565619592
b3	0.000000431583
b4	0.009257321673
b5	-0.000000149510
b6	-0.000000025719

It would be really useful if this included the final equation including both the transformation and regression coefficients, so that (for instance) it can be directly copied into a field calculator and used to calculate residuals for each point.
Besides this there are of course other uses for easy access to the actual equation.

This could look like the following (using Python code, but of course another language could be used, eg. QGIS field calculator syntax):

HTML mockup

Polynomial Order: 2

R-sqr: 0.83002

Pre-calculation Transformation Coefficients

ΔX	ΔY	ΔZ
1677454.5842407143	5658853.240481653	16.44099998474121

z = b₁ + b₂y + b₃y² + b₄x + b₅xy + b₆x²

Regression Coefficients

Coefficient Num.	Value
b1	233.745098195725
b2	-0.025565619592
b3	0.000000431583
b4	0.009257321673
b5	-0.000000149510
b6	-0.000000025719

z = 16.44099998474121 + (
	233.745098195725
	+ (-0.025565619592 * (y - 5658853.240481653))
	+ (0.000000431583 * (y - 5658853.240481653)**2)
	+ (0.009257321673 * (x - 1677454.5842407143))
	+ (-0.000000149510 * (x - 1677454.5842407143) * (y - 5658853.240481653))
	+ (-0.000000025719 * (x - 1677454.5842407143)**2)
)