[raster] GDAL's GDALFPolygonize() function

[jeanm]

Hello,

I got some inconsistency using ST_DumpAsPolygons. It turns out that when I used this function it drops one pixel. Based on this discussion (​http://lists.osgeo.org/pipermail/postgis-users/2013-June/037082.html) it looks like GDAL's GDALFPolygonize() is in fault.

Here is the reproducible example:

value's number 4 in this raster come out with ST_Value:

SELECT ST_Value(rast, 1, 8, 2), ST_BandnoDataValue(rast), ST_BandPixelType(rast)
FROM (SELECT '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'::raster rast) foo

but not with ST_DumpAsPolygons:

SELECT (ST_DumpAsPolygons(rast)).val
FROM (SELECT '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'::raster rast) foo

I used ST_Value to show that the value 4 associated with the pixel with coordinates (8,2) actually exists! Please note that adjacent values are different. Also note that ST_PixelAsPolygons() works fine.

GDAL version is 1.9.2

best regards,

Jean

[Bborie Park]

So the problem is in the function GDALFloatEquals() of alg/fpolygonize.cpp. Specifically, aInt and bInt are integers. intDiff is also an integer and is assigned the value from abs(aInt - bInt). Problem is that the difference between aInt and bInt may exceed a 32-bit integer.

This is evident when GDALFloatEquals() is called:

GDALFloatEquals(4, -1)

[robe]

Sadly this still seems to be an issue: running with {{PostgreSQL 10.1, compiled by Visual C++ build 1800, 64-bit POSTGIS="2.5.0beta2dev r16681" [EXTENSION] PGSQL="100" GEOS="3.6.3-CAPI-1.10.3 80c13047" PROJ="Rel. 4.9.3, 15 August 2016" GDAL="GDAL 2.2.4, released 2018/03/19" LIBXML="2.7.8" LIBJSON="0.12" LIBPROTOBUF="1.2.1" RASTER}}

From the mailing list thread

SELECT ST_Value(rast, 1, 8, 2), ST_BandnoDataValue(rast),
ST_BandPixelType(rast)
FROM (SELECT '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'::raster
rast) foo;

Yields:

4	-1	16BSI

but not with ST_DumpAsPolygons:

SELECT (ST_DumpAsPolygons(rast)).val
FROM (SELECT
'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'::raster
rast) foo;

Yields:

1
3
5
6
12
13
14
15
16
17
18
24
25
26
27
28
29
30
36
37
38
39
40
41
42
52
53
54
55
56
57
58
75
76
77
78
79
80
81
82
106
107
108
109
110
111
112
113
143
144
145
146
147
148
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181
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185
186
187
188