Discussion about analysis, visualization, and collaboration tools and techniques

Moderators: arango, robertson

Post Reply
Posts: 62
Joined: Fri Sep 11, 2009 1:48 pm
Location: nmefc


#1 Post by xiaozhu557 »

when i create the grid file by EASYGRID, it report a error!
In the easygrid.m files, I set
% Geographical and Grid parameters --------
lat = 0.86; % Latitude (degrees) of the bottom-left corner of the grid.
lon = 99; % Longitude (degrees) of the bottom-left corner of the grid.

X = 3120000; % Width of domain (meters) 26.33
Y = 2800000; % Length of domain (meters)
rotangle = 0; % Angle (degrees) to rotate the grid conterclock-wise
resol = 11000; % Cell width and height (i.e. Resolution)in meters. Grid cells are forced to be (almost) square.
N = 10; % Number of vertical levels

And the *_bathy.mat file is created by myself, and the area is 0.8~26.5N 98.5~131 E,resolution is 2 minutes.

??? Error using ==> qhullmx
qhull precision warning:
The initial hull is narrow (cosine of min. angle is 1.0000000000000002).
A coplanar point may lead to a wide facet. Options 'QbB' (scale to unit box)
or 'Qbb' (scale last coordinate) may remove this warning. Use 'Pp' to skip
this warning. See 'Limitations' in http://www.qhull.org/html/qh-impre.htm

qhull precision error: initial simplex is not convex. Distance=1.2e-014

While executing: | qhull d Qt Qbb Qc

Options selected for Qhull 2003.1 2003/12/30:
delaunay Qtriangulate Qbbound-last Qcoplanar-keep _pre-merge
_zero-centrum Pgood Qinterior-keep _max-width 35 Error-roundoff 1.6e-013
_one-merge 1.2e-012 Visible-distance 3.3e-013 U-coplanar-distance 3.3e-013
Width-outside 6.6e-013 _wide-facet 2e-012 _narrow-hull -2.2e-016

precision problems (corrected unless 'Q0' or an error)

flipped facets

The input to qhull appears to be less than 3 dimensional, or a
computation has overflowed.

Qhull could not construct a clearly convex simplex from points:

The center point is coplanar with a facet, or a vertex is coplanar
with a neighboring facet. The maximum round off error for
computing distances is 1.6e-013. The center point, facets and distances
to the center point are as follows:

distance= -8.9e-015

distance= -1.8e-015

distance= -1.8e-015

distance= -3.6e-015

These points either have a maximum or minimum x-coordinate, or
they maximize the determinant for k coordinates. Trial points
are first selected from points that maximize a coordinate.

The min and max coordinates for each dimension are:

0: 99 130.5 difference= 31.5

1: 0.8333 36.17 difference= 35.33

2: 0 35.33 difference= 35.33

If the input should be full dimensional, you have several options that
may determine an initial simplex:
- use 'QJ' to joggle the input and make it full dimensional
- use 'QbB' to scale the points to the unit cube
- use 'QR0' to randomly rotate the input for different maximum points
- use 'Qs' to search all points for the initial simplex
- use 'En' to specify a maximum roundoff error less than 1.6e-013.
- trace execution with 'T3' to see the determinant for each point.

If the input is lower dimensional:
- use 'QJ' to joggle the input and make it full dimensional
- use 'Qbk:0Bk:0' to delete coordinate k from the input. You should
pick the coordinate with the least range. The hull will have the
correct topology.
- determine the flat containing the points, rotate the points
into a coordinate plane, and delete the other coordinates.
- add one or more points to make the input full dimensional.

This is a Delaunay triangulation and the input is co-circular or co-spherical:
- use 'Qz' to add a point "at infinity" (i.e., above the paraboloid)
- or use 'QJ' to joggle the input and avoid co-circular data

Error in ==> delaunayn at 117
t = qhullmx(x', 'd ', opt);

Error in ==> griddata>linear at 151
tri = delaunayn([x y]);

Error in ==> griddata at 120
zi = linear(x,y,z,xi,yi,opt);

Error in ==> south_sea_easygrid at 281
h = griddata(xbathy,ybathy,zbathy,lon_rho,lat_rho,'linear');

But when I run easygrid.m and use the depth from ETOPO5 by

%This reads in worldwide bathymetry at 60 second (1 minute) resolution,
%30seconds max
xbathy = xbathy(:); %columnize
ybathy = ybathy(:); %columnize
zbathy = -zbathy(:); %columnize, and make depth positive
% outname=strcat(name,'_bathy.mat','interpreter','none')

it is OK. So I don't know the reasons when I use my depth mat file, it is created by
save south_sea_bathy xbathy ybathy zbathy

Who can tell me the reasons for that? Thank you very much!!

Posts: 23
Joined: Wed Jan 16, 2008 11:17 pm
Location: Privat

Re: EASYGRID error

#2 Post by mistral »

>> save bat.mat xbathy ybathy zbathy
xbathy = lat
ybathy = lon
zbathy = z

z = neg. in boxgeog.dat

I use Global Mapper.
impot my data
I export ascii file (first column lat second column lon third column z)
z multiplies - and change the signs.

save .dat

Post Reply