Interesting. So that adds another level of complexity of course, since that is definitely a custom CRS for QGIS! But the info I shared still probably applies. If the CRSs were built to the same specifications but in different tools (like say one data layer is coming from QGIS but another is coming from ArcGIS, both supposedly in the same CRS) QGIS can sometimes fail to see them as the same systems. Then when it goes looking for a transformation to fix the issue, it's probably not going to find one. I think my method of individually converting each layer to the QGIS version of the system would work, but that assumes there is a working custom CRS for Venus in the first place. David David Medeiros Geospatial Reference & Instruction Specialist Stanford Geospatial Center 650.561.5294 mapbliss.com SGC website: gis.stanford.edu GIS cartography: bit.ly/giscart<http://bit.ly/giscart><http://bit.ly/giscart> GIS email list: bit.ly/GISlist ________________________________ From: Diaz, Tony A. <[log in to unmask]> Sent: Friday, November 10, 2023 10:34 AM To: David Medeiros <[log in to unmask]> Subject: RE: QGIS projection question Thanks David, yes, the planet Venus. ?? From: David Medeiros <[log in to unmask]> Sent: Friday, November 10, 2023 10:33 AM To: [log in to unmask]; Diaz, Tony A. <[log in to unmask]> Subject: Re: QGIS projection question Venus as in the planet Venus? Just checking. So regardless of what the base project coordinate system is set to, if the incoming data are in a different coordinate system QGIS will need to apply an "on the fly" transformation to get them to match up visually in the projects map view. You said these are all in the same projection, but not as far QGIS is concerned, otherwise it would not be trying to use a transformation. It is possible for some standard coordinate systems to be read in by QGIS as a "custom CRS" instead. If these different layers all need to work together in QGIS then I would open each individually into a fresh QGIS project and reproject them one at a time into the known QGIS version of the CRS that's needed. Then try to open them together to see if the transformation issue has been resolved. Good luck! David David Medeiros Geospatial Reference & Instruction Specialist Stanford Geospatial Center 650.561.5294 mapbliss.com SGC website: gis.stanford.edu GIS cartography: bit.ly/giscart GIS email list: bit.ly/GISlist ________________________________ From: Maps-L: Map Librarians, etc. <[log in to unmask]<mailto:[log in to unmask]>> on behalf of Diaz, Tony A. <[log in to unmask]<mailto:[log in to unmask]>> Sent: Friday, November 10, 2023 9:07 AM To: [log in to unmask]<mailto:[log in to unmask]> <[log in to unmask]<mailto:[log in to unmask]>> Subject: QGIS projection question Hi all, I have a student who is trying to load in a Venus global map data but when they try to align different maps with the same projection, or even change projection, they get an error (consistently) "No transform available between XXXX and Custom CRS”. Any ideas or resources I could point them to? Thanks, Tony Diaz Caltech Pasadena, CA