survey_animation = function()
---[[  '--' at start to disable animation, '---' to enable
	local minx, miny, maxx, maxy = surface_bounds(Definitions)
	-- ensure 1px of white background all around
	-- just in case the viewport ever goes
	-- outside canvas bounds while animating
	minx,miny, maxx,maxy = minx-1,miny-1, maxx+2,maxy+1
	local zoomx = App.screen.width/(maxx-minx)
	local zoomy = App.screen.height/(maxy-miny)
	local zoom, cw, ch
	if zoomx < zoomy then
		zoom = zoomx
		cw = maxx-minx
		ch = cw*App.screen.height/App.screen.width
	else
		zoom = zoomy
		ch = maxy-miny
		cw = ch*App.screen.width/App.screen.height
	end
	Global_viewport = {x=minx, y=miny, w=cw, h=ch, zoom=zoom}
	snapshot_canvas()
	-- initialize animation
	Animating = {
		copy_viewport(Global_viewport),
		copy_viewport(Viewport),
	}
	Viewport.x = -App.screen.width/2
	Viewport.y = -App.screen.height/2
	Viewport.w = App.screen.width
	Viewport.h = App.screen.height
	Viewport.zoom = 1.0  --]]
end