Question on UTM to Screen Conversion

[Evan Preston]

GRASS programming gurus:

I have been trying (unsuccessfully) to solve the following problem:

I want to be able to take a UTM coordinate (within my current region), and
convert it to screen coordinates so that I may use the R_panel_save routine
to save the "chunk" of map surrounding the UTM position.  Here's a section of
my code (not the entire program):

void flash (char *icon)
{
  FILE                  *file;
  int                   i, t, b, l, r;
  char                  cmd[256],
                        *panel;
  struct Cell_head      region;
  double                y,
                        x,
                        east,
                        north;

  /* initialize  grass libraries */
  G_gisinit("flash");
 
  /* read in easting and northing */
  file = fopen(icon, "r");
  fscanf(file, "%lf %lf", &east, &north);
  fclose(file);
 
  R_open_driver();
  D_setup(0);

  /* get screen max, min */ 
  t=R_screen_top();
  b=R_screen_bot();
  l=R_screen_left();
  r=R_screen_rite();

  /* convert E, N to screen coords, define panel size, save panel */
  G_get_window(&region);
  D_get_screen_window(&t,&b,&l,&r);
  D_do_conversions(&region,t,b,l,r);
  y=D_u_to_d_row(north);
  x=D_u_to_d_col(east);

  /* define box */ 
  t=y+10;
  b=y-10;
  r=x+10;
  l=x-10;

  /* save map "chunk", draw a simple box, then restore map "chunk" */
  panel = G_tempfile();
  R_panel_save(panel,t,b,l,r);
  R_standard_color(1);
  R_box_abs(l,t,r,b); 
  R_panel_restore(panel);
  R_panel_delete(panel);
  R_close_driver();
} 

The screen coordinates, and region parameters sent to D_do_conversions appear
"normal", as follows:

east=228947.683604 
north=4412208.345485
screen window: 0 829 0 1144 (top bottom left right)
Cell_head info: 
	North:	4762270.000000 
	South:	3650770.000000 
	West:	-103279.000000 
	East:	877763.000000 
	ew-res: 7109.000000 
	ns-res: 8892.000000

The results from the call to D_u_to_d_row and D_u_to_d_col are as follows:

	y=1095816396.000000 x=1091302045.000000

	(Shouldn't these numbers be somewhere between the original screen limits
	of 0-829 and 0-1144??)

Consequently, when I add and subtract constants from these numbers to define the
size of a box, I am getting the following type of nasty X errors (right after
the call to R_panel_save).

	X Error of failed request:  BadMatch (invalid parameter attributes)
  	  Major opcode of failed request:  73 (X_GetImage)
	  Serial number of failed request:  1485
	  Current serial number in output stream:  1485
	ERROR eof from graphics driver.


Any ideas whats causing this program to blow up?  Many thanks in advance!

################################################################################
#     Evan B. Preston                            # Battelle                    #
#     phone:     614.424.3983                    # National Security Division  #
#     fax:       614.424.3776                    # 505 King Ave.               #
#     internet:  preston at malibu.dst.battelle.org # Columbus, Ohio  43201       #
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