I just downloaded QGIS 3.0 on Mac OS X but I could not find TIN interpolation plugin in the Search & manage plugin. Is there something wrong with the Mac version of QGIS 3?
According to the changelog, the TIN interpolation plugin has been removed, as it is now part or QGIS core.
To find it in Qgis 3.0, open the processing toolbox and search for Interpolation -> TIN interpolation.
Some of the plugins are "deprecated" for this version of QGIS, they need to be upgraded/ moved within the QGIS 3.0 environment. Here is some info for Plugin Devs that you can read to maybe help you understand the concept "Ported Over"
Considering QGIS 3.0 is in early release, if you desparately need the functionality of that Plugin I recommend using QGIS 2 considering it is "Long Term Deployment" and the plugins are up to date.
You can try download a zipped version of the plugin from Github or the QGIS Plugin Repo from a web browser (Google the plugin name) and install it via the "Install From Zip" option in the plugin window, if it works, great, but it should then tell you if the plugin is compatible
By now you may have resolved issue pertaining to TIN or IDW. If you are working with QGIS 3.4.3-Madeira, then, go to View from the Menu Bar, and then go to Panels. Check Processing Toolbox under Panels. You will then see a Processing Toolbox in your QGIS screen. It should be in right hand side as pane. In the search box of Processing Tool, type Interpolation and it will come up with both TIN and IDW. Double click any of them and you will get what you wanted. Hope it helps. Surface dimension model is not hard to create under TIN or IDW interpolation in QGIS. You just need to be methodical in your steps. You do not need Interpolation Plugin in QGIS 3.4.3.
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