How can I pick extended intersecting point as dimension origin?
Extended I mean is, entities doesn't actually intersect but can intersect if extended.
You can place a point at the intersection by selecting both the lines and then click on point. This will add a point at the intersection which can be used for dimensioning.
What Deepak refers to is the creation of what we call a Virtual Sharp in SolidWorks. The following help topic refers to sketches, but it actually also works in drawings (I have already used the "feedback on this topic" link to alert the documentation department to update the topic to indicate that fact). Within that topic is a link to another help topic that indicates how to control the display of virtual sharps.
You can create construction lines representing the extension
then place a point at that intersection.
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