[Octave-bug-tracker] [bug #65362] patch may not produce a polygon

[Liang Tang]

URL:
  <https://savannah.gnu.org/bugs/?65362>

                 Summary: patch may not produce a polygon
                   Group: GNU Octave
               Submitter: lt1234
               Submitted: Sat 24 Feb 2024 10:42:19 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: lt1234
        Originator Email: 
             Open/Closed: Open
                 Release: 8.2.0
         Discussion Lock: Any
        Operating System: Microsoft Windows
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Sat 24 Feb 2024 10:42:19 PM UTC By: Liang Tang <lt1234>
Hi, 

patch may not display a polygon.  Pls see the attached figure files.  Thanks,



The small example demonstrates a compatibility issue, or an error.

% CCW order, P0 is estimated from plane_1=@(x) [1 2 3 ]*x-06;  

P0=[6  4 -4 
    0 -2 -4
    0 -6  6 
    6 -6  3]; 
 

The P0 patch display, two triangles with one point intersection, is not a
polygon and is incompatible with matlab, i.e., two triangles with line 1-3
intersection.   It does not matter if the intersection is line 1-3 or line
2-4, the output is a polygon.   

figure;   hold on; 
for ii=1:size(P0,1), text(P0(ii,1), P0(ii,2), P0(ii,3), num2str(ii),
'fontsize', 20); end ; 
patch(P0(:,1), P0(:,2), P0(:,3), 'r', 'facealpha', 0.1);  xlabel('x');
ylabel('y'); 
saveas(gcf, 'patch_P0.ofig'); 
%view([235 30])  

A minor modification to P0(1,2) (y=3, instead y=4) change the display
completely.   
    
figure;   
subplot(1,2,1); hold on; 
for ii=1:size(P0,1), text(P0(ii,1), P0(ii,2), P0(ii,3), num2str(ii),
'fontsize', 20); end 
patch(P0(:,1), P0(:,2), P0(:,3), 'r', 'facealpha', 0.1); hold on; xlabel('x');
ylabel('y'); 
subplot(1,2,2); hold on; 
P0(1,2)=3; 
for ii=1:size(P0,1), text(P0(ii,1), P0(ii,2), P0(ii,3), num2str(ii),
'fontsize', 20); end 
patch(P0(:,1), P0(:,2), P0(:,3), 'r', 'facealpha', 0.1); hold on; xlabel('x');
ylabel('y'); title('Modified P0(1,2)')

saveas(gcf, 'patch_P0_update.ofig'); 







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File Attachments:


-------------------------------------------------------
Name: patch_p0.zip  Size: 14KiB
<http://savannah.gnu.org/bugs/download.php?file_id=55743>

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