topic Re: slope analysis in ArcGIS Spatial Analyst Questions

slope analysis

KunomBersh — Wed, 10 Oct 2018 15:21:14 GMT

I have a line feature with elevation value, I need to extract a point along the line where its slope percentage is out of the range (-0.05 to 0.05), what I tried was I created a number of points by featureverticestopoint with all option, I got a big point data, then I tried to compare slope from one point to the other but I could not come up which point are out of the range, to keep their location, I need a python script, that loop each slope from point to point.

Re: slope analysis

DanPatterson_Retired — Wed, 10 Oct 2018 22:48:53 GMT

I can think of an exploratory tool

Profile graph—Charts | ArcGIS Desktop

and one to extract the data itself from a slope map by densifying a polyline at the point density you want,

Densify—Help | ArcGIS Desktop

and convert it to points, then

Feature To Point—Data Management toolbox | ArcGIS Desktop with the vertices option

Generate Points Along Lines—Data Management toolbox | ArcGIS Desktop

then

Extract by Points—Help | ArcGIS Desktop

Re: slope analysis

KunomBersh — Thu, 11 Oct 2018 01:16:05 GMT

Thanks Dan Patterson, your input is helpful all the time , but I need to go further, please refer drawing

The intention is to find out which point has slope percentage out of the range (-0.05 to 0.05), if the average slope from p1 to p2 is in the range “pass or ignore”, and compare p1 to p3 if the slope within the range, jump to compare p1 to p4 if the slope is out of the range, record p4 as deflation point, then start compare from p4 to p5, if it is within the range pass, compare p4 to p6 if it is out of the range record p6 and then again start from p6, and compare p6 to p7 so on….the deflation point will be the starting point for comparison with the next point, if we have millions of points how we can automate using python.

Re: slope analysis

DanPatterson_Retired — Thu, 11 Oct 2018 01:48:07 GMT

Kunom, that is a different beast.

The 'slope' you will be calculating isn't the slope that you would get from performing a slope analysis on a raster.

What you need to do is get the X, Y, and Z (ie elevations) at your points of interest.

You then convert the sequential X, Y values to a distance from the origin, which is P1 in your figure.

P2, etc are some distance from P1 etc etc.

The denser the point network along your line, the finer the gradient you can calculate.

Essentially if your points are sequential in a table, then the calculation can be made as a first pass by calculating the differential slope between points.

ie (Z2-Z1)/d1 where Z is elevation and 'd' is the distance.

so generically, (Zn - Zn-1)/dn

Those are your first order differences. Find the break where the values are out of range, if any.

Do you have the X, Y and Z values in tabular form... or a facsimile of your data that you could post?

I could demonstrate the sequential calculations.

And I presume by millions of points... you mean in one file? or many files? Doesn't really matter except for the number of times that the process needs to be done. (I don't need a million for now, just a reasonable sample)

A simple demo

Re: slope analysis

KunomBersh — Thu, 11 Oct 2018 11:46:41 GMT

If this help

OBJECTID	X	Y	Z
1	-9912775	4941760	799.2415
2	-9912775	4941761	799.2293
3	-9912776	4941762	799.2181
4	-9912777	4941763	799.2112
5	-9912778	4941764	799.209
6	-9912778	4941765	799.2097
7	-9912779	4941766	799.2114
8	-9912780	4941767	799.2168
9	-9912781	4941769	799.2236
10	-9912781	4941770	799.2313
11	-9912782	4941771	799.2404
12	-9912783	4941772	799.2533
13	-9912783	4941773	799.2662
14	-9912784	4941774	799.2735
15	-9912785	4941775	799.2767
16	-9912785	4941776	799.2816
17	-9912786	4941778	799.2919
18	-9912787	4941779	799.3056
19	-9912787	4941780	799.3157
20	-9912788	4941781	799.3154
21	-9912788	4941782	799.3109
22	-9912789	4941782	799.3076
23	-9912789	4941783	799.2908
24	-9912790	4941784	799.2706
25	-9912790	4941786	799.2495
26	-9912791	4941787	799.2285
27	-9912792	4941788	799.2075
28	-9912792	4941789	799.1864
29	-9912793	4941790	799.1654
30	-9912794	4941791	799.1443
31	-9912794	4941793	799.1233
32	-9912795	4941794	799.1023
33	-9912795	4941795	799.0812
34	-9912796	4941796	799.0602
35	-9912797	4941797	799.0404
36	-9912797	4941797	799.0391
37	-9912797	4941798	799.0181
38	-9912798	4941800	798.9971
39	-9912799	4941801	798.976
40	-9912799	4941802	798.955
41	-9912800	4941803	798.9342
42	-9912800	4941804	798.9146
43	-9912801	4941805	798.8954
44	-9912802	4941807	798.8756
45	-9912802	4941808	798.8538
46	-9912803	4941809	798.8242
47	-9912804	4941810	798.7867
48	-9912804	4941811	798.7425
49	-9912805	4941812	798.6963
50	-9912805	4941813	798.683
51	-9912805	4941813	798.653
52	-9912806	4941815	798.6123
53	-9912807	4941816	798.5735
54	-9912807	4941817	798.5344
55	-9912808	4941818	798.4982
56	-9912809	4941819	798.4673
57	-9912809	4941820	798.4457
58	-9912810	4941822	798.4284
59	-9912810	4941823	798.4145
60	-9912811	4941824	798.4006
61	-9912811	4941825	798.39
62	-9912812	4941825	798.3826
63	-9912812	4941826	798.3574
64	-9912813	4941827	798.3253
65	-9912814	4941829	798.2879
66	-9912814	4941830	798.2465
67	-9912815	4941831	798.2021
68	-9912815	4941832	798.1575
69	-9912816	4941833	798.1141
70	-9912817	4941834	798.0771
71	-9912817	4941835	798.0486
72	-9912818	4941837	798.0263
73	-9912819	4941838	798.0092
74	-9912819	4941839	797.9945
75	-9912820	4941840	797.98
76	-9912821	4941841	797.9674
77	-9912821	4941842	797.962
78	-9912822	4941843	797.9667
79	-9912823	4941845	797.9784
80	-9912823	4941846	797.99
81	-9912824	4941847	797.998
82	-9912825	4941848	798.0028
83	-9912825	4941849	798.0045
84	-9912826	4941850	798.002
85	-9912827	4941851	797.9969
86	-9912828	4941852	797.9919
87	-9912828	4941854	797.9875
88	-9912829	4941855	797.9814
89	-9912830	4941856	797.9724
90	-9912830	4941857	797.9611
91	-9912831	4941858	797.9479
92	-9912832	4941859	797.9317
93	-9912833	4941860	797.9119
94	-9912833	4941861	797.8921
95	-9912834	4941862	797.8757
96	-9912835	4941863	797.8628
97	-9912835	4941865	797.851
98	-9912836	4941866	797.8403
99	-9912837	4941867	797.8343
100	-9912838	4941868	797.8315
101	-9912838	4941869	797.8311
102	-9912839	4941870	797.8284
103	-9912840	4941871	797.8216
104	-9912841	4941872	797.8121
105	-9912842	4941873	797.8044
106	-9912842	4941874	797.8014
107	-9912843	4941875	797.8087
108	-9912844	4941876	797.8206
109	-9912845	4941877	797.8306
110	-9912845	4941878	797.8365
111	-9912846	4941880	797.8416
112	-9912847	4941881	797.8509
113	-9912848	4941882	797.8697
114	-9912849	4941883	797.8926
115	-9912849	4941884	797.9158
116	-9912850	4941885	797.9366
117	-9912851	4941886	797.9515
118	-9912852	4941887	797.9579
119	-9912852	4941888	797.9564
120	-9912853	4941889	797.9519
121	-9912854	4941890	797.9506
122	-9912855	4941891	797.9586
123	-9912856	4941892	797.9795
124	-9912856	4941893	798.0113
125	-9912857	4941894	798.0506
126	-9912858	4941895	798.089
127	-9912859	4941896	798.1145
128	-9912860	4941898	798.1302
129	-9912860	4941899	798.1413
130	-9912861	4941900	798.1485
131	-9912862	4941901	798.1525
132	-9912863	4941902	798.1537
133	-9912863	4941903	798.154
134	-9912865	4941905	798.154