how to place a suspended object with surf - matlab

Question

I am writing a code to produce a house with a given height, width, length, and angle of sloped roof.
I was able to produce the walls with surf by using a zero value for a specific dimension, allowing a wall to be made as an x-y plane, x-z plane, etc.
However, Now I am trying to produce a desk inside that is an x-y plane with a specific height, and cant figure out how..
MATLAB says it needs a matrix, but a matrix formed only from the height doesn't work, also using ndgrid(heightValue:.5:heightValue) doesn't work
If anyone knows how to help, I would greatly appreciate it.
Code:
(one of the desk sides is in the wrong place as well for similar problems, but help with this problem will allow me to figure out how to fix it)
clear; clc; close all;
%% INPUT VARIABLES
lengthdlg = 'Please enter length of base (m): ';
widthdlg = 'Please enter width of base (m): ';
heightdlg = 'Please enter height of wall (m): ';
angledlg = 'Please enter the angle of the roof (degrees): ';
dlgbox = inputdlg({lengthdlg, widthdlg, heightdlg, angledlg},...
'Simple AutoCAD', [1 50; 1 50; 1 50; 1 50], {'30','40','15','30'});
BaseL = str2double(dlgbox(1));
BaseW = str2double(dlgbox(2));
WallH = str2double(dlgbox(3));
RoofA = str2double(dlgbox(4));
m = tand(RoofA);
h = figure;
set(h,'name','Simple AutoCAD House','numbertitle','off')
xlabel('x'),ylabel('y'),zlabel('z')
title('Simple AutoCAD House')
colormap white
%% Base/Floor
[xB,yB] = ndgrid(0:1:BaseL, 0:1:BaseW);
zB = (xB*0);
surf(xB,yB,zB,'FaceColor','k')
hold on
%% Walls
%Front Wall (w/Door opening)
[xFW,zFW] = ndgrid(0:1:BaseL, 0:1:WallH);
yFW = (xFW*0);
yFW(xFW>.4*BaseL & xFW<.6*BaseL & zFW<.8*WallH) = nan;
surf(xFW,yFW,zFW);
hold on
%Back Wall
[xBW,zBW] = ndgrid(0:.5:BaseL, 0:.5:WallH);
yBW = (xBW*0)+BaseW;
surf(xBW,yBW,zBW);
%Right Wall
[yRW,zRW] = ndgrid(0:.5:BaseW, 0:.5:WallH);
xRW = (yRW*0)+BaseL;
surf(xRW,yRW,zRW);
%Left Wall
[yLW,zLW] = ndgrid(0:.5:BaseW, 0:.5:WallH);
xLW = (yLW*0);
xLW(yLW>.25*BaseW & yLW<.75*BaseW & zLW>.5*WallH & zLW<.7*WallH) = nan;
surf(xLW,yLW,zLW);
%% Roof
%Left Panel
[xLP,yLP] = ndgrid(0:.5:(BaseL/2), 0:.5:BaseW);
zLP = (m*xLP)+WallH;
surf(xLP,yLP,zLP)
hold on
%Right Panel
[xRP,yRP] = ndgrid((BaseL/2):.5:BaseL, 0:.5:BaseW);
zRP = (-m*xRP)+(WallH+m*BaseL);
surf(xRP,yRP,zRP)
%% Roof Triangles
%Front Triangle
[xFT,zFT] = ndgrid(0:.25:BaseL, WallH:.25:(m*BaseL/2)+WallH);
yFT = 0*xFT;
yFT(zFT>(m*xFT+WallH)) = nan;
yFT(zFT>(-m*xFT+(m*BaseL+WallH))) = nan;
surf(xFT,yFT,zFT)
%Back Triangle
[xBT,zBT] = ndgrid(0:.25:BaseL, WallH:.25:(m*BaseL/2)+WallH);
yBT = (xBT*0)+BaseW;
yBT(zBT>(m*xBT+WallH)) = nan;
yBT(zBT>(-m*xBT+(m*BaseL+WallH))) = nan;
surf(xBT,yBT,zBT)
%% Door
[xD,zD] = ndgrid(.4*BaseL:.5:.6*BaseL, 0:.5:.8*WallH);
yD = xD*0;
door = surf(xD,yD,zD,'FaceColor','g');
%% Windows
%Left Window
[yLWin,zLWin] = ndgrid(.25*BaseW:.5:.75*BaseW, .5*WallH:.5:.75*WallH);
xLWin = (yLWin*0);
surf(xLWin,yLWin,zLWin,'FaceAlpha',.25,'FaceColor','b')
%% Desk and chair
%desktop
[xDT,yDT] = ndgrid(.8*BaseL:.5:.99*BaseL, .7*BaseW:.5:.99*BaseW);
zDT = (0*xDT);
surf(xDT,yDT,zDT,'FaceColor','r')
%DeskNear
[xDN,zDN] = ndgrid(.8*BaseL:.5:BaseL, 0:.5:.25*WallH);
yDN=(0*zDN)
surf(xDN,yDN,zDN,'FaceColor','r')
%% Door Opening
k = waitforbuttonpress;
if k == 0
delete(door)
end

Answer 1

The ZData property of a surface, is the z coordinate for each point in the surface. In your example, you set it to the right size by making it the same size as your XData and YData; however, the way you construct your ZData is a little off. You essentially do this:
zDT = (0 * xDT);
What this effectively does, is forces the z coordinate of every point in the mesh to be 0 (i.e. on the floor). This is why the desk top simply sits on the floor, and also why the side of the desk sits on the side of the wall (y = 0).
To fix this, you want to instead calculate what the values should actually be rather than setting them to zero.
Desktop
The nice thing is that the z value for the entire desktop is actually a constant for the whole surface since it's parallel to the floor. You define what the height of the desktop is when you create the side of the desk.
[xDN, zDN] = ndgrid(.8*BaseL:.5:BaseL, 0:.5:.25*WallH);
Here you're saying the height of the desk is 0.25 * WallH rounded to the previous 0.5 (because of your step size). So we want to set the ZData of the desktop to be that value (the max of zDN) and we can multiply that value by a matrix of ones the size of the XData to make it the right size.
zDT = max(zDN(:)) * ones(size(xDT));
Side of Desk
For the side of the desk, the issue isn't the ZData anymore, it's now the YData. As it currently is, you have it set to all zeros so it get's stuck to the wall at y = 0.
yDN = (0 * zDN);
Again, we want the y value to be constant for the whole side of the desk. We can compute what this y value is by using the minimum y value from the desk top (again, making sure it's the right size by using a matrix of ones).
yDN = min(yDT(:)) * ones(size(xDN));
Summary
We can make those two changes and this makes the bottom portion of your code look something like this.
%desktop
[xDT,yDT] = ndgrid(.8*BaseL:.5:.99*BaseL, .7*BaseW:.5:.99*BaseW);
[xDN,zDN] = ndgrid(.8*BaseL:.5:BaseL, 0:.5:.25*WallH);
zDT = max(zDN(:)) * ones(size(xDT));
surf(xDT,yDT,zDT,'FaceColor','r')
%DeskNear
yDN = min(yDT(:)) * ones(size(xDN));
surf(xDN,yDN,zDN,'FaceColor','r')
If we apply that, we get the desktop off of the floor and the side of the desk where it belongs.
As Amro said in the comment to your post, it will likely be much easier to draw this sort of thing using patch rather than surf as it gives you a great deal more flexibility as far as shapes.

Answer 2

Here is my version of the house :)
Code should be easy to follow. Note that I'm using the patch function instead.
% input measurements
BaseL = 30;
BaseW = 40;
WallH = 15;
RoofA = 30;
% colors
m = tand(RoofA);
clr = hsv(10);
clf
% floor
patch([0 1 1 0].*BaseL, ...
[0 0 1 1].*BaseW, ...
[0 0 0 0].*WallH, clr(1,:));
% front wall (w/ door opening)
patch([1 1 0 0 0.4 0.4 0.6 0.6].*BaseL, ...
[0 0 0 0 0 0 0 0].*BaseW, ...
[0 1 1 0 0 0.8 0.8 0].*WallH, clr(2,:));
% back wall
patch([0 1 1 0].*BaseL, ...
[1 1 1 1].*BaseW, ...
[0 0 1 1].*WallH, clr(3,:));
% right wall
patch([1 1 1 1].*BaseL, ...
[0 0 1 1].*BaseW, ...
[0 1 1 0].*WallH, clr(4,:));
% left wall (w/ window opening)
patch([0 0 0 0 0 0 0 0 0 0 0 0].*BaseL, ...
[0 0 0.5 0.5 0.25 0.25 0.75 0.75 0.5 0.5 1 1].*BaseW, ...
[0 1 1 0.7 0.7 0.5 0.5 0.7 0.7 1 1 0].*WallH, clr(5,:));
% roof left/right panels
patch([0 0.5 0.5 0].*BaseL, ...
[0 0 1 1].*BaseW, ...
[0 1 1 0].*(m*BaseL/2)+WallH, clr(6,:));
patch([1 0.5 0.5 1].*BaseL, ...
[0 0 1 1].*BaseW, ...
[0 1 1 0].*(m*BaseL/2)+WallH, clr(7,:));
% roof front/back triangles
patch([0 1 0.5].*BaseL, ...
[0 0 0].*BaseW, ...
[0 0 1].*(m*BaseL/2)+WallH, clr(8,:));
patch([0 1 0.5].*BaseL, ...
[1 1 1].*BaseW, ...
[0 0 1].*(m*BaseL/2)+WallH, clr(9,:));
% door
hDoor = patch([0.4 0.6 0.6 0.4].*BaseL, ...
[0 0 0 0].*BaseW, ...
[0 0 0.8 0.8].*WallH, 'k', 'FaceAlpha',0.75);
% window on left wall
hWin = patch([0 0 0 0].*BaseL, ...
[0.25 0.75 0.75 0.25].*BaseW, ...
[0.5 0.5 0.7 0.7].*WallH, 'k', 'FaceAlpha',0.75);
% table inside
patch([0.8 0.99 0.99 0.8].*BaseL, ...
[0.7 0.7 0.99 0.99].*BaseW, ...
[0.2 0.2 0.2 0.2].*WallH, clr(10,:));
patch([0.8 0.99 0.99 0.8].*BaseL, ...
[0.7 0.7 0.7 0.7].*BaseW, ...
[0.01 0.01 0.2 0.2].*WallH, clr(10,:));
patch([0.8 0.99 0.99 0.8].*BaseL, ...
[0.99 0.99 0.99 0.99].*BaseW, ...
[0.01 0.01 0.2 0.2].*WallH, clr(10,:));
% 3D view
axis([0 BaseL 0 BaseW 0 WallH*2]), axis vis3d
view(3), grid on
xlabel('X'), ylabel('Y'), zlabel('Z')
title('Simple AutoCAD House')
% animate door/window transparencies
t = linspace(-pi,pi,20);
anim = #(t) 1-(tanh(t)+1)/2; % smooth function from 1 to 0
for i=1:numel(t)
set([hDoor,hWin], 'FaceAlpha',anim(t(i)))
pause(0.1)
end
There is a small animation at the end, where the door and window go from tinted to clear. Hope you like it!