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Topics - mbarker

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General / Trouble aligning FLIR Thermovision 1000 images
« on: November 06, 2024, 09:43:33 PM »
Hello,
I am working with a historic imageset that came from a thermal scanning system in the early 2000s. The model is a FLIR Thermovision 1000. I found a copy of the user manual here:  [FLIR Thermovision 1000 manual][https://www.yumpu.com/en/document/read/48814512/thermovision-1000-flir-customer-support-center-flir-systems]. I have GPS x,y coordinates that I have written into the images' EXIF and estimated altitude based on reported GSD. Upon visual inspection, images appear to have ~70 % overlap. However, I am uncertain of values I should use for focal length and sensor size, and I assume this is why I am failing to get images aligned. I have seen others successfully produce orthomosaics with the same sensor, but I have been unable to find parameters they may have used. Any help would be greatly appreciated!

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Hello,

I am working with a relatively large area of interest (~160 acres), that was broken up into 4 flights. Imagery was acquired with a Micasense Altum. I treat each flight as its own chunk, and essentially follow this workflow:

import folder
align photos
import and adjust GCP markers
optimize cameras
gradual selection and reoptimize cameras until satisfactory error is achieved
reflectance calibration (panel only, clear day)
dense cloud
merge chunks
Build DEM from dense cloud
Build orthomosaic from DEM(normalize band sensitivity is checked)
raster transform, dividing bands 1-5 by 32768, and converting thermal centikelvin to Celsius
Export ortho as bigTIFF with raster transform set to index values

The main problem I am encountering is that when I merge the chunks this is somehow impacting the reflectance calibration. The reflectance values are lower than if I export orthomosaics from individual chunks. This effect is apparent immediately when I merge chunks because the images appear darker (I am using the same reference band in merged and individual chunks: NIR). Also, it is severe enough that I can see flight lines of different flights when visually assessing the raster in GIS software.

What is going wrong, and how can I remedy the situation? Any advice would be greatly appreciated.

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