VRML surface conic projection

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andre padilla
andre padilla 2020-4-7
评论： andre padilla 2020-4-12
How can i do a conic projection of a surface in VRML format ?
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darova
darova 2020-4-7
Is this correct?
Do you know how the cone is situated?
andre padilla
andre padilla 2020-4-7
Yes of course
i know where the cone is situated and what is its solid angle
and the distance from its top to the geometrical center of the surface
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回答（3 个）

darova
darova 2020-4-8
Here is an idea:
  • Projection onto cone: if your data in cartesian system - convert it to polar ()
New radius of projected data
  • Create flat projection:
New limits of angle:
New limits or radius:
See also HERE and HERE
andre padilla
andre padilla 2020-4-11
May be i did not sufficiently esplain the problem.
I generated in another software a colored surface of an arbitrary shape model (its not a sphere or an an ellipsoide ...)
This surface is in VRML 2 format.
I was wondering how it is possible to use a MATLAB function to generate a conic projection of this colored model surface.
Seems that existing MATLAB functions may produce conic projections of spheres or may be flatened spheroides
So these are not applicable for a random shaped objject. And one other problem is that those geographic MATLAB
functions do not read VRML format.
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andre padilla
andre padilla 2020-4-11
Do you think that i can use this kind of strategy
MATLAB commands :
landareas = shaperead('landareas.shp','UseGeoCoords',true);
axesm ('eqaconic', 'Frame', 'on', 'Grid', 'on');
geoshow(landareas,'FaceColor',[1 1 .5],'EdgeColor',[.6 .6 .6]);
tissot;
Of course i have to convert
my_object_surface.wrl to my_object_surface.shp
How to do that ?
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darova
darova 2020-4-11
Can you attach the data?

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andre padilla
andre padilla 2020-4-11
Yes of course.
the file need to be renamed to .gz and gunziped
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darova
darova 2020-4-11
I uploaded this program to read your file: LINK
Inside the program i changed this line (someone in comments to this script did the same)
keynames=char('Coordinate','point','coordIndex','color');
Then used this script to import to MATLAB and make a projection
[nel,w3d,infoline] = read_vrml1('myscene.wrl');
%%
cla
pts = w3d(1).pts;
fv.vertices = pts;
fv.faces = w3d(1).knx;
patch(fv,'facecolor','g')
a = 60;
[X,Y] = meshgrid(-20:20); % grid for cone
Z = 40-1/tand(a)*sqrt(X.^2+Y.^2); % Z coordinate of cone
surface(X,Y,Z,'facecolor','none','edgecolor','y')
[td,rd] = cart2pol(pts(:,1),pts(:,2)); % convert data to polar system
L0 = rd*sind(a) + (40-pts(:,3))*cosd(a);
r0 = L0 * sind(a); % new radius
zd = 40-L0 * cosd(a); % new Z coordinate
[xd,yd] = pol2cart(td,r0,pts(:,3)); % conert to cartesian
fv1.vertices = [xd yd zd];
fv1.faces = fv.faces;
patch(fv1,'facecolor','r')
light
axis vis3d equal
Unfortunately i didn't find a way to import colors
Honestly: looks like
Is it you wanted? Or you wanted flat projection?
andre padilla
andre padilla 2020-4-12
thanks,
that is a first way i will try to find to get the colors
Many thanks
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