Download P3Dv6 SDK here:
www.prepar3d.com
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If you do actually have P3Dv6 'properly' installed:
When installing P3Dv6 SDK, allow it to use its own internally assigned Drive / Folder Paths; this by default will be in:
C:\Program Files\Lockheed Martin\Prepar3D v6 SDK 6.1.10.31609\
After P3Dv6 SDK is installed, ADE should find this SDK automatically when it starts up ...
IF you actually have P3Dv6 properly installed.
ADE Startup Mode Prompt > Choose:
P3Dv6
FYI: If ADEv1.79x has no startup Mode for P3Dv6, bear in mind that ADE was only partially compatible with P3Dv5 when Jon retired.
I do not have P3Dv5 or P3Dv6 installed, so you may- or may not- find that ADE can work with all features / requirements of P3Dv6.
...You can 'try' this, however:
If you do not have P3Dv6 'properly' installed, or it is not actually installed on your computer:
...Select a P3D numeric version that
is installed.
Then, navigate:
ADE Menu > Tools >
New User Wizard > Complete / Verify / Update Info In All Sequenced Dialog Boxes > {Folders} > Use P3Dv6 paths:
SHP2VEC Compiler Path: C:\Program Files\Lockheed Martin\Prepar3D v6 SDK 6.1.10.31609\World\Terrain\
SHP2VEC.exe
BglComp Path: C:\Program Files\Lockheed Martin\Prepar3D v6 SDK 6.1.10.31609\World\Scenery\
BglComp.exe
If you do not actually have a version of P3D installed, your ability to use ADE with P3D SDK may vary with each P3D SDK version chosen.
Generally speaking, most- but not all- FSX scenery made in ADE using P3Dv1.4x SDK will still display in all P3D versions.
https://www.fsdeveloper.com/forum/resources/prepar3d-v1-sdk.227/
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GaryGB