[gdal-dev] Odd Contours

Owen Varley Owen.Varley at inzpire.com
Mon May 18 05:32:05 PDT 2020

Hi all,

I'm seeing some odd contour line points being generated from gdal_contour and I was wondering whether anything else might have seen something similar?

Using gdal_contour -i 15.24 -a height e100n00.dt2 n00.shp on the attached tile (Removed as too large) gives some contours which have points very close together. Take a look at the first three points in the contour line below, there are all < 0.1m of each other which, given the height posts are spaced at 30m's, seems very odd.

Contour Line (381m):
(100.1727777777963, 0.5436111111111112)
(100.17277777777778, 0.5436111111039885)
(100.17277777770833, 0.5436111111111112)
(100.1725, 0.5437345679012346)
(100.17222222222223, 0.5438518518518518)
(100.1720833332639, 0.5438888888888889)
(100.17222222222223, 0.5440277778472222)
(100.1724074074074, 0.5441666666666667)
(100.1725, 0.5442222222222222)
(100.17277777777778, 0.5443888888888889)
(100.17305555555556, 0.5442592592592592)
(100.17314814814816, 0.5441666666666667)
(100.1731944445139, 0.5438888888888889)
(100.17305555555556, 0.5438562091503267)
(100.1727777777963, 0.5436111111111112)

Related DTED height posts (m):
       [371, 374, 377, 380, 379, 379]
       [376, 379, 382, 385, 382, 379]
       [379, 383, 386, 390, 383, 379]
       [368, 368, 377, 381, 366, 375]
       [364, 357, 347, 342, 329, 345]

Has anyone seen this before or know what is going on? For the majority of other contours the contour points are at least 30m apart.

Kind regards,


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