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I'm currently working with Cassini data, particularly of Saturn's moon Enceladus. I'm trying to use QGIS to visualize and measure craters on its surface, however, the CRS doesn't seem to be working. Every time I try to measure a distance in ellipsoidal coordinates I obtain 'nan' instead of a value. enter image description here

This is the coordinate reference system the image is using)

PROJCRS["SimpleCylindrical ENCELADUS",
    BASEGEOGCRS["GCS_ENCELADUS",
        DATUM["D_ENCELADUS",
            ELLIPSOID["ENCELADUS",252100,0,
                LENGTHUNIT["metre",1,
                    ID["EPSG",9001]]]],
        PRIMEM["Reference_Meridian",0,
            ANGLEUNIT["degree",0.0174532925199433,
                ID["EPSG",9122]]]],
    CONVERSION["Equidistant Cylindrical",
        METHOD["Equidistant Cylindrical",
            ID["EPSG",1028]],
        PARAMETER["Latitude of 1st standard parallel",0,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8823]],
        PARAMETER["Longitude of natural origin",180,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["False easting",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",0,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1,
                ID["EPSG",9001]]]]

Is there a way to make it so I can measure ellipsoidal distances (instead of just nan's) on my raster?

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  • What is the coord system of the project? The measurement tool will use the projects coordinate system as you are interacting with the map canvas. Maybe just double check that the project coord system is the same as the data source.
    – nr_aus
    Nov 7 at 2:30
  • Please, go to QGIS "Help" menu > "About" and copy/paste version details. Nov 7 at 5:17
  • @swiss_knight Heres the version details... QGIS version: 3.22.5-Białowieża QGIS code revision: 2a0a86f142 Qt version: 5.14.2 Python version: 3.8.7 GDAL/OGR version 3.2.1 PROJ version 6.3.2 EPSG Registry database version v9.8.6 (2020-01-22) GEOS version: 3.9.1-CAPI-1.14.2 SQLite version: 3.31.1 PostgreSQL client version: 12.3 SpatiaLite version: 4.3.0a QWT version 6.1.4 QScintilla2 version 2.11.4 OS version macOS 12.6 Active Python plugins Coregistration 22.5.19 processing 2.12.99 sagaprovider 2.12.99 grassprovider 2.12.99 db_manager 0.1.20 MetaSearch 0.3.5 Nov 18 at 16:34

1 Answer 1

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Using a sample downloaded from:

https://planetarymaps.usgs.gov/mosaic/Enceladus/enceladus_cassini_iss_shapemodel_bland_2019/enceladus_2019pm_topography.tif

and the embedded CRS, measuring ellipsoidal coordinates results into nan m as well, but switching to Cartesian returns plausible results (500 km from the top to the bottom, with Enceladus' radius of ~252 km)

So takeaway: maybe you just need to select the Cartesian distance measuring method?

enter image description here

Embedded CRS:

PROJCRS["unnamed",
BASEGEOGCRS["unknown",
DATUM["unknown",
ELLIPSOID["unnamed",251500,0,
LENGTHUNIT["metre",1,ID["EPSG",9001]]]],
PRIMEM["Greenwich",0,
ANGLEUNIT["degree",0.0174532925199433,ID["EPSG",9122]]]],
CONVERSION["Equidistant Cylindrical",
METHOD["Equidistant Cylindrical",
ID["EPSG",1028]],
PARAMETER["Latitude of 1st standard parallel",0,
ANGLEUNIT["degree",0.0174532925199433],ID["EPSG",8823]],
PARAMETER["Longitude of natural origin",180,
ANGLEUNIT["degree",0.0174532925199433],
ID["EPSG",8802]],
PARAMETER["False easting",0,LENGTHUNIT["metre",1],
ID["EPSG",8806]],
PARAMETER["False northing",0,LENGTHUNIT["metre",1],
ID["EPSG",8807]]],
CS[Cartesian,2],
AXIS["easting",east,ORDER[1],LENGTHUNIT["metre",1,
ID["EPSG",9001]]],
AXIS["northing",north,ORDER[2],LENGTHUNIT["metre",1,
ID["EPSG",9001]]]]

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