for some datasets we are overzooming them by a signficiant amount to align them to a output tile matrix zoom level.
For example a 1M DEM will be overzoomed to z18 0.59m, z17 is 1.19M it is closer to the 1M but is slightly lower quality.
By adding --base-zoom-offset=-1 we can force cogify to underzoom some datasets where to save storage space.
This can also be used with more zoom offsets to create signficantly smaller output files for a sample dataset whanganui_2022_0.075m which by default creats 20GB of COGs at z21.
By using -3 or -4 can greatly reduce the size of the dataset
Reducing Webp quality from 90% to 80% quality can additionally reduce the output file size even further. ~200MB for z18.
Modifications
Adds a configuration option --base-zoom-offset to allow configuration of the output COGs base zoom level.
Adds a preset webp80 to reduce the quality target for webp from 90% to 80%
Verification
I have manually created many testing datasets with the new cogify to validate file sizes and image quality.
Motivation
for some datasets we are overzooming them by a signficiant amount to align them to a output tile matrix zoom level.
For example a 1M DEM will be overzoomed to z18 0.59m, z17 is 1.19M it is closer to the 1M but is slightly lower quality.
By adding
--base-zoom-offset=-1we can force cogify to underzoom some datasets where to save storage space.This can also be used with more zoom offsets to create signficantly smaller output files for a sample dataset
whanganui_2022_0.075mwhich by default creats 20GB of COGs at z21.By using
-3or-4can greatly reduce the size of the datasetReducing Webp quality from 90% to 80% quality can additionally reduce the output file size even further. ~200MB for z18.
Modifications
Adds a configuration option
--base-zoom-offsetto allow configuration of the output COGs base zoom level. Adds a preset webp80 to reduce the quality target for webp from 90% to 80%Verification
I have manually created many testing datasets with the new cogify to validate file sizes and image quality.