OK, it worked as vrt of a vrt. Memory not an issue.
But I have a new problem. One vrt I want to instead do > -29 (caspian sea, -29
in SRTM data). The whole region evaluates to 1 (true). It looks like the
in_ar[] is getting truncated to an unsigned byte, 0-255, from its orignal
Int16. Testing some values, anything up to 254 gives me 0/1 areas matching the
elevation values in the original DEM, but >255 returns 0 for the whole area
(that is, everything >255 was truncated to 255, so nothing is >255). Thus, >
-29 is true for the whole area.
I tried using the python cmp() function, in case the () test was casting each
value to Byte, but it complained that it's ambiguous for an array. The error
suggested to use a.any() or a.all(), but I don't know how to do that one.
Here is the script again:
import numpy
def land(in_ar, out_ar, xoff, yoff, xsize, ysize, raster_xsize, raster_ysize,
buf_radius, gt, **kwargs):
out_ar[:] = (in_ar[0] > -29)
> On Apr 26, 2018, at 1:07 PM, William Kyngesburye <[email protected]>
> wrote:
>
> So, if the gdal library queries for a region of the vrt (ie processing it in
> chunks), the numpy array will be just that region? I'll give it a try.
>
> What about something like viewing the whole vrt in QGIS - will it be read in
> chunks as well? IOW, is it the GDAL library that breaks it into chunks at
> reading, or is it the responsibility of programs (gdal_translate, QGIS,...)
> to ask for chunks?
>
>> On Apr 26, 2018, at 12:59 PM, Even Rouault <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> On jeudi 26 avril 2018 12:56:10 CEST William Kyngesburye wrote:
>> > So, a vrt of a vrt?
>>
>> Yes
>>
>> >
>> > I wanted to avoid that, because as I understand the source, it reads each
>> > raster in the derived band as a single numpy array, which would be all the
>> > tiled rasters together.
>>
>> No, if you use gdal_translate, it will process the source by reasonable
>> chunks, so you should be able to process arbitrarily large sources.
>>
>> Even
>>
>> --
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> -----
> William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
> http://www.kyngchaos.com/ <http://www.kyngchaos.com/>
>
> "We can die but once, and that once we must die. To be always fearing, then,
> would not avert it, and would make life miserable."
>
> - Tarzan, on death
>
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-----
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http://www.kyngchaos.com/
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offal?
Second Pogril: I don't know. Why IS life like sticking your head in a bucket
filled with hyena offal?
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