feat(editor): the tracks laid on the terrain model go onto it as the tracks going onto the terrain do, the chain laid since the laying began fitted again at each click, with the tracks around kept and met; a straight or an arc cut by the fit before made one again, a path cut only where it would part from the line by more than 3 cm; a choice of the heights while laying: fitted, from point to point, level, kept in the settings; the fit taken back with its click

application/editormode.h

@@ -436,8 +436,6 @@ class editor_mode : public application_mode, private editor_track::observer, pri
 	void nmt_follow_tracks();
 	// the height the ground will have where the terrain is made ahead of the track laid and isn't there yet
 	bool nmt_ahead(double const X, double const Z, double &Height) const;
-	// a track laid through the points gets its formation from the terrain of the model: it needn't keep to every bump of it
-	bool nmt_formed(std::vector<glm::dvec2> const &Points) const;
 	// the squares of the model under the rectangle are in, none of them waiting to be asked for again
 	bool nmt_ready(glm::dvec2 const &Min, glm::dvec2 const &Max);
 	// Only: the paths of these tracks are shaped anew, the modifiers of those removed taken away; null: all of them. the number
@@ -466,8 +464,18 @@ class editor_mode : public application_mode, private editor_track::observer, pri
 	std::size_t nmt_join_ends();
 	void nmt_auto_start();
 	void nmt_auto_step();
-	// the grade line of the line of tracks through the track fitted to the terrain model and applied; false if it couldn't be
-	bool nmt_fit_line(TTrack &Track);
+	// the grade line of the line of tracks through the track fitted to the terrain model and applied; false if it couldn't be.
+	// The line runs over the tracks not Fitted, the ones fitted stay as they are and the line meets them. Where the model falls
+	// away under the line by the abutments the tracks go over on a bridge; Laid: the tracks just laid, the formation fills it and
+	// they are cut only where they can't follow the line otherwise
+	bool nmt_fit_line(TTrack &Track, std::function<bool(TTrack const *)> const &Fitted, bool const Laid);
+	// the tracks laid in one go since the history step From put onto the terrain model as one line, as the tracks go onto the
+	// terrain: the track ending at End then the one the laying goes on from
+	bool nmt_fit_laid(std::size_t const From, glm::dvec3 const End);
+	// the tracks laid one after another on one straight or one arc, cut by the grade lines fitted before, made one again
+	void nmt_merge_laid(std::unordered_set<TTrack const *> &Laid);
+	// the points of the paths of the track about a metre apart, in squares of the plan
+	static void nmt_sample_paths(TTrack const &Track, std::map<std::pair<int, int>, std::vector<nmt_state::laid_point>> &Points);
 	// the tool of the terrain the left mouse button works
 	enum class terrain_tool
 	{
@@ -1384,6 +1392,7 @@ class editor_mode : public application_mode, private editor_track::observer, pri
 			glm::dvec3 point{0.0};
 		};
 		std::vector<step> chain;
+		std::size_t history{0}; // the step of the history the chain was begun at
 	};
 	lay_tool m_lay;
 	bool m_norms_free{false};
@@ -2335,7 +2344,7 @@ class editor_mode : public application_mode, private editor_track::observer, pri
 	void profile_check();
 	// Terrain: the heightmap terrain follows the tracks changed. Bridges: stretches of the route over a bridge or a viaduct, the
 	// paths over them cut off at their ends and set to the bridge environment
-	void profile_apply(bool const Terrain = false, std::vector<profile::departure> const &Bridges = {});
+	void profile_apply(bool const Terrain = false, std::vector<profile::departure> const &Bridges = {}, double const Fewest = 0.0);
 	// the terrain under the tracks changed by the last Edits steps of the history which changed tracks
 	void profile_follow_terrain(std::size_t const Edits);
 	void profile_fit_view();