path = path or Path("Follow")
    local tries = 0
    local viable = path:Compute(self, pos, function( area, fromArea, ladder, elevator, length )
        if tries > 20000 then
            return -1
        end
        tries = tries + 1
        if ( !IsValid( fromArea ) ) then
            // first area in path, no cost
            return 0
        else

            if not self:CanFitInArea(area) then
                return -1
            end

            if ( !self.loco:IsAreaTraversable( area ) ) then
                // our locomotor says we can't move here
                return -1
            end

            // compute distance traveled along path so far
            local dist = 0

            if ( IsValid( ladder ) ) then
                dist = ladder:GetLength()
            elseif ( length > 0 ) then
                // optimization to avoid recomputing length
                dist = length
            else
                dist = ( area:GetCenter() - fromArea:GetCenter() ):GetLength()
            end

            local cost = dist + fromArea:GetCostSoFar()

            // check height change
            local deltaZ = fromArea:ComputeAdjacentConnectionHeightChange( area )
            if ( deltaZ >= self.loco:GetStepHeight() ) then
                if ( deltaZ >= self.loco:GetMaxJumpHeight() ) then
                    // too high to reach
                    return -1
                end

                // jumping is slower than flat ground
                local jumpPenalty = 5
                cost = cost + jumpPenalty * dist
            elseif ( deltaZ < -self.loco:GetDeathDropHeight() ) then
                // too far to drop
                return -1
            end
            return cost
        end
    end)