topic Re: ResizeContour in GDL

ResizeContour

John Edmundson — Thu, 01 Oct 2026 23:25:21 GMT

Does anyone have a simple example of using the "ResizeContour" command? It can be as small as a 10'x10' box that is made 5' larger with the command. I have been trying to understand the POLYGON OPERATIONS EXTENSION (GDL Reference Guide - page 647) without success. I wish the manual had included a simple example.

Thanks

Re: ResizeContour

rudl — Wed, 07 Oct 2026 15:56:03 GMT

Don't know that extension but
You could have your poly curve in a twodimensional array and use the following code (created with help oh chatgpt)
and later use the parameter buffer to feed the POLY2

offset the offset you want (constant edge offset)
working_profile is the input array use working_profile = your array before running the sub
profile_off is the output array
profile_off_reset array to clear profile off just in case.

"offsetpoly": profile_off = profile_off_reset FOR i = 1 TO nProfile IF i = 1 THEN ip = nProfile ELSE ip = i - 1 ENDIF IF i = nProfile THEN in = 1 ELSE in = i + 1 ENDIF ! -------------------------------------------------------- ! EDGE 1: previous -> current ! -------------------------------------------------------- dx1 = profile_working[i][1] - profile_working[ip][1] dy1 = profile_working[i][2] - profile_working[ip][2] len1 = SQR(dx1 * dx1 + dy1 * dy1) nx1 = dy1 / len1 ny1 = -dx1 / len1 ! -------------------------------------------------------- ! EDGE 2: current -> next ! -------------------------------------------------------- dx2 = profile_working[in][1] - profile_working[i][1] dy2 = profile_working[in][2] - profile_working[i][2] len2 = SQR(dx2 * dx2 + dy2 * dy2) nx2 = dy2 / len2 ny2 = -dx2 / len2 ! -------------------------------------------------------- ! POINTS ON THE TWO OFFSET LINES ! -------------------------------------------------------- x1 = profile_working[i][1] - nx1 * offset y1 = profile_working[i][2] - ny1 * offset x2 = profile_working[i][1] - nx2 * offset y2 = profile_working[i][2] - ny2 * offset ! -------------------------------------------------------- ! INTERSECTION ! -------------------------------------------------------- denom = dx1 * dy2 - dy1 * dx2 IF ABS(denom) > 0.000001 THEN t = ((x2 - x1) * dy2 - (y2 - y1) * dx2) / denom profile_off[i][1] = x1 + t * dx1 profile_off[i][2] = y1 + t * dy1 ELSE ! Parallel / 180° corner profile_off[i][1] = x1 profile_off[i][2] = y1 ENDIF NEXT i profile_working = profile_working_reset RETURN

Re: ResizeContour

John Edmundson — Fri, 09 Oct 2026 15:30:50 GMT

Thank you. This certainly achieves the results I was after. I have been trying to use the "DICTIONARY" (page 647) functions since they seem powerful for POLY objects. I expanded your code to draw a POLY and offset it, and it produces the results I am looking for. Thank you. If I can figure out how to use the DICTIONARY function, I will post the solution.

Expanded Code for offset POLY

!=============================

dim profile_working[][]

dim profile_working_reset [][]

dim profile_off[][]

dim profile_off_reset[][]

!===================================================

nProfile = 5

offset = -2'

!===================================================

profile_working[1][1] = 0'

profile_working[1][2] = 0'

profile_working[2][1] = 10'

profile_working[2][2] = 0'

profile_working[3][1] = 15'

profile_working[3][2] = 5'

profile_working[4][1] = 5'

profile_working[4][2] = 10'

profile_working[5][1] = -3'

profile_working[5][2] = 4'

!===================================================

profile_off = profile_off_reset

FOR i = 1 TO nProfile

IF i = 1 THEN

ip = nProfile

ELSE

ip = i - 1

ENDIF

IF i = nProfile THEN

in = 1

ELSE

in = i + 1

ENDIF

! --------------------------------------------------------

! EDGE 1: previous -> current

! --------------------------------------------------------

dx1 = profile_working[i][1] - profile_working[ip][1]

dy1 = profile_working[i][2] - profile_working[ip][2]

len1 = SQR(dx1 * dx1 + dy1 * dy1)

nx1 = dy1 / len1

ny1 = -dx1 / len1

! --------------------------------------------------------

! EDGE 2: current -> next

! --------------------------------------------------------

dx2 = profile_working[in][1] - profile_working[i][1]

dy2 = profile_working[in][2] - profile_working[i][2]

len2 = SQR(dx2 * dx2 + dy2 * dy2)

nx2 = dy2 / len2

ny2 = -dx2 / len2

! --------------------------------------------------------

! POINTS ON THE TWO OFFSET LINES

! --------------------------------------------------------

x1 = profile_working[i][1] - nx1 * offset

y1 = profile_working[i][2] - ny1 * offset

x2 = profile_working[i][1] - nx2 * offset

y2 = profile_working[i][2] - ny2 * offset

! --------------------------------------------------------

! INTERSECTION

! --------------------------------------------------------

denom = dx1 * dy2 - dy1 * dx2

IF ABS(denom) > 0.000001 THEN

t = ((x2 - x1) * dy2 - (y2 - y1) * dx2) / denom

profile_off[i][1] = x1 + t * dx1

profile_off[i][2] = y1 + t * dy1

ELSE

! Parallel / 180° corner

profile_off[i][1] = x1

profile_off[i][2] = y1

ENDIF

NEXT i

profile_working = profile_working_reset

! Base Poly ===================================================

poly2 5, 1+4,

profile_working[1][1], profile_working[1][2],

profile_working[2][1], profile_working[2][2],

profile_working[3][1], profile_working[3][2],

profile_working[4][1], profile_working[4][2],

profile_working[5][1], profile_working[5][2]

! Offset Poly ===================================================

poly2 5, 1+4,

profile_off[1][1], profile_off[1][2],

profile_off[2][1], profile_off[2][2],

profile_off[3][1], profile_off[3][2],

profile_off[4][1], profile_off[4][2],

profile_off[5][1], profile_off[5][2]

!===================================================