Details Ticket 1182


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Serial Number 1182
Subject grass5.1 d.vect doesn't show all lines falling within zoomed display
Area grass5.7
Queue grass
Requestors matti.aarnio@zmailer.org
Owner none
Status resolved
Last User Contact Wed Aug 31 13:40:00 2005 (3 yr ago)
Current Priority 30
Final Priority 70
Due No date assigned
Last Action Wed Aug 31 13:40:00 2005 (3 yr ago)
Created Tue Jul 9 15:19:30 2002 (6 yr ago)

Transaction History Ticket 1182


Tue, Jul 9 2002 15:19:30    Request created by guest  
Subject: grass5.1 d.vect  doesn't show all lines falling within zoomed display
Apparently if a 2D vector has at least one of its end points within the active
display area, whole visible subsegment is shown successfully.

When a subsegment just intersects the display area and both its end points are
outside, either the line is not drawn at all, or is drawn with wrong colour.
This appears with Grass 5.1 d.vect from CVS of about a week ago.

This shows symptoms of classical computer graphics vector visibility problem,
and should be fairly easy to fix by following algorithms in basic computer
graphics books.  (Unfortunately I have misplaced my reference books, and can't
fix it right away.)

Does it happen with 5.0, I have not verified. I have used 5.1's 3D vectors to
model various buildings and other constructs at a hilltop.
Tue, Jul 9 2002 15:44:22    Mail sent by guest  
Cannot confirm. Both 2D/3D work for me.

Radim
Wed, Jul 10 2002 15:16:55    Comments added by guest  
Initially I observed this at a black base X display, where I drew some
boundary lines, and measured site spots.  When zooming in, some of those
boundary lines disappeared.

I have a 2D vertex set:

L  7
 497.420 398.156
 593.463 425.459
 533.600 517.400
 548.360 613.690
 509.920 669.000
 440.770 593.270
 497.420 398.156

Working initially at  g.region w=0 s=0 n=1000 e=1000 res=0.1, inputting
that set with  v.in.ascii,  and then plotting this on GRAY background:

  d.erase color=gray
  d.vect map=testset-1 color=red

Now change the displayed region:

  g.region n=580 s=448 w=470 e=650 res=0.1
  d.redisplay

and you should see what I mean.

It is possible that lines which are merely intersecting the visibility
region are drawn with BLACK color, instead of set color (RED).

The more I am playing with the case, the more I suspect this is an issue
with plotted vertex color becoming BLACK at odd moments.  I just had a case
where one building outline line set became completely black, while being
fully inside the visibility area.

And of course, nothing excludes (so far) a possibility of this being
a compiler bug:
  gcc version 3.1 20020619 (Red Hat Linux Rawhide 3.1-6.1)

...
successive  d.redraw  runs cycled the building outline in question from
all in correct color, to progressingly more in wrong color -- AND again
all in correct color..
Wed, Jul 10 2002 16:20:12    Mail sent by guest  
I have got:

http://mpa.itc.it/radim/draw1.png
http://mpa.itc.it/radim/draw2.png

in grass5.1/grass5. 

May be also bug in grass, which appears only in gcc 3.1. 

Last 3 rows of your last reply, I don't understand. 
(maybe report as new bug in grass50)

Radim
Tue, Jul 16 2002 11:36:18    Area changed to grass5.1 by bernhard  
Wed, Jan 22 2003 10:50:22    Mail sent by mneteler  
Hi

does this problem still exist?

Markus
Mon, Aug 25 2003 16:50:15    Mail sent by mneteler  
Today's status:

Unfortunately this problem is still there.
Probably the clipping algorithm when drawing a map?

v.digit shows it as well.
Reproducable in XDRIVER and PNG driver.

Markus
Mon, Oct 20 2003 18:14:15    Area changed to grass5.7 by mneteler  
Mon, Aug 2 2004 13:14:58    Comments added by guest  
If you underlay a raster for reference, is the clipping actually just the
extent of the region when the display monitor and region settings have
different aspect ratios? I saw something similar when digitizing lines with
5.7's v.digit with a big null border on either side. Had me confused for a while.
Hamish
Sat, Jul 23 2005 12:39:56    Mail sent by msieczka  
Matti (or anybody)

Does this problem still exist in 6.0 or 6.1?

Maciek

Please "reply to all" so I receive a copy directly.
Wed, Aug 31 2005 13:40:00    Status changed to resolved by msieczka  
Wed, Aug 31 2005 13:40:00    Mail sent by msieczka  
Apparently resolved as nobody's answered within 1,5 month. Closing it. Please
let me know if I should reopen.

Maciek
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