[QGIS-Developer] QgsRasterLayer is very slow for rasters with a higher number of bands

[Benjamin Jakimow]

Dear all,

it seems that QGIS has big problems to load rasters with a higher number 
of bands. De facto users cannot visualize data from hyperspectral 
satellites like EnMAP, DESIS or the CHIME in a responsive way.

In my case I tried to load an AVIRIS-NG image (425 bands x 1673 height x 
649 width, float, interlave=band) into QGIS. It took me more than half a 
minute until it appeared in the layers list and a much more time until 
it was rendered. In comparison, ArcMap showa the image almost immediately.

I did some benchmarks to compare how fast 1673x649 px images get loaded 
using plain GDAL and a QgsRasterLayer:
(a) ang_bsq_3bands.tif - 16 MB, a 3 band subset
(b) ang_bsq_425bands.tif – 2.3 GB, all 425 bands

I don’t care about some milliseconds difference, but it shows that even 
the creation of the QgsRasterLayer is very very slow.

	

	

	

ang_bsq_3bands

	

ang_bsq_425bands

/Initialize Dataset / QgsRasterLayer/

gdal.Open(path)

	

34 ms

	

16 ms

QgsRasterLayer(path) (1)

	

2462 ms

	

70247 ms

QgsRasterLayer(path) (2)

	

1348 ms

	

70048 ms

/Load a random single band/

gdal.Band.ReadAsArray()

	

63 ms

	

72 ms

layer.dataProvider().block(b, …) (1)

	

206 ms

	

57013 ms

layer.dataProvider().block(b, …) (2)

	

163 ms

	

70915 ms

(1)Using QgsRasterLayer.LayerOptions(loadDefaultStyle=False)

(2)Using QgsRasterLayer.LayerOptions(loadDefaultStyle=True)

Both images and my benchmark.py are available here: 
https://box.hu-berlin.de/d/c688ab6a8545414aaa16/
The original image (ang20180702t105516_rdn_v2q2) with line-interleave 
can be downloaded from the AVIRS-NG data portal 
https://avirisng.jpl.nasa.gov/dataportal/

Maybe I have used the QGIS API in a wrong way or simply need to deactive 
a QGIS setting and everything becomes fine, but so far I could'nt find 
such a setting.

Should I open a github issue for that?

Greetings,
Benjamin


-- 
Benjamin Jakimow, Doctoral Researcher
Earth Observation Lab | Geography Department | Humboldt-Universität zu Berlin

e-mail:benjamin.jakimow at geo.hu-berlin.de

phone:  +49 (0) 30 2093 6846
mobile: +49 (0) 157 5656 8477
fax:    +49 (0) 30 2093 6848
mail:   Unter den Linden 6 | 10099 Berlin | Germany
room: 2'211
web:https://hu-berlin.de/eo-lab
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