Height maps

  "xvalue",  "yvalue",  "zvalue"  // Coordinates
  |          |          |
  V          V          V
, 336415.50, 390170.75, 60.78  // First vertex
, 336210.30, 390373.05, 53.03  // Second vertex
, 336280.20, 390472.90, 58.20  // Third vertex
  

grid position: 200, 200, y
data positions: (closest points to the grid position)
D1: 150, 100, 100
D2: 300, 120, 130
D3: 120, 250, 80
D4: 270, 290, 200
'
          dX    dZ   Y 
DeltaD1: -50, -100, 100 (150-200, 100-200, 100)
DeltaD2: 100,  -80, 130 (300-200, 120-200, 130)
DeltaD3: -80,   50, 80  (120-200, 250-200, 80)
DeltaD4:  70,   90, 200 (270-290, 290-200, 200)
'
// weighted linear interpolation along first x axis
X1y = (100*100 + 130*50) / (50+100)   // 110 
X1z = (100*100 + 120*50) / (50+100)   // 106.667
'
// weighted linear interpolation along second x axis
X2y = (80*70 + 200*80) / (80+70)      // 144 
X2z = (250*70 + 290*80) / (80+70)     // 271.333
'
// weighted linear interpolation along first z axis
Z1y = (100*50 + 80*100) / (100+50)    // 86.667
Z1x = (150*50 + 120*100) / (100+50)   // 130
'
// weighted linear interpolation along second z axis
Z2y = (130*90 + 200*80) / (80+90)     // 162.941
Z2x = (300*90 + 270*80) / (80+90)     // 285.882
'
DX1z = 200-X1z // 93,333
DX2z = X2z-200 // 71.333  -- Delta must be positive!
DZ1x = 200-Z1x // 70
DZ2x = Z2x-200 // 85.882
'
PX = (DX1z*X2y + DX2z*X1y) / (DX1z+DX2z) // 129.271
PZ = (DZ1x*Z2y + DZ2z*Z1y) / (DZ1x+DZ2x) // 120.918
y = PX + PZ / 2                          // 125.095
'
Grid: 200, 200, 125.095
'
'
'     *(150,100)
'                  *(300,120)
'
'
'         +(200,200)
'
'   *(120,250)          
'                *(270,290)
'--------------------------
'     *
'         ^(200,106*
'         |
'(130,200)|
'    ^----+-------^(286,200)
'         |
'   *     ^(200,271)
'                *

  

x: 0                75    100
   *----------------+-----*
y: 50               H     130

H = (50*25 + 130*75) / (25+75)
H = 25% of 50 + 75% of 130

H(50) = (50 + 130) / 2

This works for any values of x and y.. 
X could start 523.233 and end at 781.64 and solve H at 600.


H(600) = ((600-523.233)*50 + (781.64-600)*130) / (781.64-523.233)
 

To make it more logic in 2d drawing is X horizontal, Y vertical and Z height..

Point: (XYZ)

Points: A , B, C, D, E, F, G, H, I  <- A, B, C, D are known at start.
Lines: AB, CD, AC, BD, EF, GH 
      
  (0,0)                       (500,0) Z is not listed
      A------E----------------B
      |      |                |
      |      |                |
      G------I----------------H
      |      |(200,200)       |
      |      |                |
      |      |                |
      |      |                |
      |      |                |
      C------F----------------D
(0,500)                       (500,500)
E = AB(X=200)  <- Find the (XYZ) point at position X=200 in the line.
F = CD(X=200)
G = AC(Y=200)
H = BD(Y=200)
I = ( GH(X=200) + EF(Y=200) ) / 2        <- GH(200) and EF(200) doesn''t neccesarrily have the same value for Y)

 

p=[336020.85,390863.55,53.00,336030.55,390448.55,48.20,... all the points];
X=p(1:3:end); Y=p(2:3:end); Z=p(3:3:end);

N  = 128;
xh = linspace(min(X),max(X),N);
yh = linspace(min(Y),max(Y),N);
[XH,YH] = meshgrid(xh,yh);
ZH = griddata(X,Y,Z,XH,YH,'v4');