关于PNG图像在CAD中的换算比例

背景

简单介绍一下，最近做了一个点云切片管理的小工具，点云切片来自于JRC软件导出的PNG图像和scr文件，而PNG的dpi会不一样，而scr描述文件里却只有一个缩放因子，所以在内部做处理时比较麻烦，无法获取图像实际所占位置。

scr文件

;JRC Reconstructor orthophoto import command sequence into AutoCAD
;This script imports the orthophoto "limian_5_002_hjz.png" into AutoCAD, keeping the original orthophoto size in meters.
;The position and orientation that the orthophoto had in Reconstructor is also exported to AutoCAD.
;Furthermore, a new UCS called "UCS_from_limian_5_002_hjz" will be created in AutoCAD,
;with the same position and orientation of the orthophoto.
;A new layer called "limian_5_002_hjz" will be created in AutoCAD to contain the orthophoto.
;The length measure unit selected for this script is Meters.
;
;----------------------------------------script
(setq old-insunits (getvar "insunits"))
insunits 6
(setq old-osmode (getvar "osmode"))
_osmode 0
_ucs _w
_ucs _na _d "UCS_from_limian_5_002_hjz"
_ucs _3 21.290760281751879,8.6897138827298299,-1.6033916170721909 20.290760281751879,8.6897138827298299,-1.6033916170721909 21.290760281751879,8.6897138827298299,-0.60339161707219091
_ucs _na _s "UCS_from_limian_5_002_hjz"
_plan _c
_layer _m "limian_5_002_hjz" _c 140 "limian_5_002_hjz"

_plan _c
-image _A "limian_5_002_hjz.png"
0,0,0 2.00000000000(此处为缩放因子) 0
(setvar "osmode" old-osmode)
(setvar "insunits" old-insunits)
_qsave
;-------------------------------------endscript
;
;GEXCEL

通过切8000，10000，12000三个长度的切片，最后测试得到换算大概是

实际长度(厘米)=像素 * 0.0264550265 * 缩放因子