Advanced GIS Exam 2
How is a multipatch different than an extruded object?
-Has multiple z values. Creates 3D structures
What is a keyframe and how is it used to construct an animation?
-where we select camera to focus on in animation, GIS moves from one keyframe to another.
What is a Web Scene? How is a Web Scene created, stored, and used?
ArcGIS Online able to publish as a web scene Publish on ArcGIS Online Take data publish as web scene and give url to be opened
What are the values assigned to a backlink grid and how is it used in calculating the Least-Cost Path?
Back link grid: Every cell have a value indicating which direction to move in to have the least cost Value assigned to each grid cell of which direction to move to get back to the source (least cost route) Works for any location out there (based on the constraints we use) (slope and land use in powerpoint)
Why is Lidar considered an active remote sensing system?
Because the sensor generates its own source of energy and sends it out to receive the return of that same energy
What is a US Topo?
Been around for 10 years No longer producing paper sheets Now produced as a pdf from the national map Special pdj (geopdj) acts like a mini gis Switch layers on and off and can download onto machine Modern day topo map 300 a day for free
How is a Least-Cost path calculated from the destination back to the source (by using the Cost-weighted distance grid)?
Big picture version: start at the destination (location) and work backwards to a source Gives path for every cell back to a source Calculates least cost for each cell, takes the lowest and assigns it a value 1-8 with a directional link
How are LAS files used in ArcGIS?
Bring together LAS files into a LAS dataset. Allow you to ingest multiple LAS files to work with in GIS Take all the tiles and LAS files and brings them together
How can multiple constraints (and multiple weighted constraints) be used in building a Cost-Weighted grid?
Combined into one cost weighted grid by adding cells
What is a LAZ file?
Compressed version of a LAS file
What is "cost" in relation to raster distance calculations?
Cost for moving laterally = 1 unit Cost for moving diagonally = 1.414
What is a Lidar DSM and what is it measuring?
Digital Surface Model → height of things on top of the ground are measured Measurement of the ground elevation and areas above the ground Model you create from Lidar
What is a DLG?
Digital line graphs Downloaded contours from the scanned topo maps
What is a DRG?
Digital raster graphic USGS product: scanned old topo maps (High res) and georeferenced them to match other GIS data (just a scan not the actual contours)
How are contours extracted by using GIS data such as a DEM?
Directly off a DEM Take a DEM and tell GIS it to generate contour lines from the DEM (find areas of equal elevation) and how often to draw the lines
What is CityEngine and how is it used?
ESRI's Large scale 3D urban design/planning program. Does not use drones or planes flying over top. It makes large scale urban planning and design with GIS
How are the features of a TIN stored in GIS?
Elevation (z) values stored in the nodes Connect points together with edges (breakline) Storage: more complex items we deal with Store all relationships between points independent of actual latitude and longitude Needs to know adjacent faces, nodes that make it up, the coordinates of these nodes and faces, is it a hard or soft line... Massive amount of data
How is accumulated cost calculated (in both the horizontal and diagonal directions)?
Everytime you move laterally = 1 unit Everytime you move diagonally 1.414 units Add the total movements up and multiple by resolution Each cell represents a real world distance
What is a Delaunay Triangle and why is it important to the TIN creation process?
Fat triangle: get edges close to 60 degrees as possible Minimize variation in the landscape Delaunay triangulation puts points together in a fashion that tries to get the landscape in fat triangles Delaunay triangle: can draw a circle through all 3 points in the triangle (near perfect)
What is the difference between a first and a last return (in regards to what they are measuring)?
First Return: initial bounce back off an object Last Return: energy transmitted through an object that will bounce off another object Multiple returns = multiple height measurements at same x,y locations Get 2 height measurements for the same height In general, last returns are always measuring the ground
What does each value in the ASPRS Lidar classification stand for (in terms of its class description)?
Formal classification Lidar Classifications 0 = Never classified 10 = Rail 1 = Unassigned 11 = Road surface 2 = Ground 12 = Reserved 3 = Low vegetation 13 = Wire/guard (Shield) 4 = Medium vegetation 14=Wire/Conductor(Phase) 5 = High vegetation 15 = Transmission Tower 6 = Building 16 = Wire-Structure Connector 7 = Low point 17 = Bridge Deck 8 = Reserved 18 = High Noise 9 = Water 19-63 = Reserved
What are the components of a Lidar system and how are they used?
GPS → track the position of the plane (x,y, and z) IMU → inertial measurement unit (tracks plane position) plane does not fly straight all the time Recorder → computer to record the data (each one of the x,y,z coordinates and measurements) All together = Lidar System
What are the general features of a surface model / digital terrain model in GIS?
Generate an elevated surface Accurately represent surface Suitable for data collection Minimize data storage Maximize data handling suitable for surface analysis
What is a prism map and how is a prism map read?
Give us a way to assess thematic map data Extrude particular layers of a map Allows us to map two things at once, using color to represent one item and extrusion to represent another. Not extruding in feet, but instead vertical units. You can accentuate the representation with vertical exaggeration. Altering the vertical scale but leaving the horizontal scale the same.
How does grid cell resolution affect the distances traveled in a raster network?
Grid cell resolution gives the real world distance in which you would travel based on the number of units
What is the difference between a hard and a soft breakline in a TIN?
Hard breakline:a definite discontinuity in the surface (edge that cannot have elevation change as you go across Soft breakline: any other edge you use is a soft breakline imaginary lines you need to put together for a tin
What are some real-world applications of Lidar?
High resolution topography in small areas in a better resolution Measurements of storm impact (hurricanes) Assess damages ( dune removal buildings destroyed) Model coastal ecosystems Tree canopy measurements (health and growth) Urban planning → calculate highly accurate 3D models of structures would look like drought/flood mapping
What is a System Style in ArcGIS Pro and how is it used in 3D visualization?
How we want to change symbology, can use for many 3D symbols System style allows access to 3D things such as cars and trees
What is Allocation and how does it operate?
If we have multiple sources allocation tells us for every grid cell what source that grid cell is closest to Used for a lot of things: Identify customers served by a series of stores Which hospital is closest Shortage of fire hydrants in an area Areas not served by a supermarket
What is a contour?
Imaginary line that joins points of equal elevation above or below the datum
How is Cost-Weighted Distance determined for each cell? (i.e. what are the steps involved with starting with an initial grid of cost-weighted values and using that to create a cost-weighted distance grid)?
Impedance (add to our cost) (slow us down) Cost of 1st cell plus cost of second cell Divided by the number of surfaces you traverse Cost of moves is now dependant on the impedance values Cost Weighted Algorithm: need set of sources to calculate distance from And cost weighted grid (increase cost based on factors in way) Find cost weighted distance to each adjacent cell from the source Pick the value with the least cost and search for adjacent cells from there Continue with the next least cost cells until cost-weighted grid is full
How do Lidar DTM results compare to coarser DEMs? Why is this?
Lidar DTM: able to generate fine resolution DEM (1m) Coarser DEMs: (30-10m) barely any detail - rough detail Much more detailed DEM with 1m
What is Lidar and what does the term mean?
Light Detection and Ranging We use laser beams (different wavelength than microwaves)
What is a multipatch?
Making 2.5D polygon into full 3D
What is "draping" and how can images (such as digital maps, aerial photos or satellite images) be displayed in pseudo-3D in GIS using a TIN?
Match up layers with the TIN Draping take data match up corresponding points and raise/lower accordingly
How is a Lidar measurement made?
Measured in distance. Altitude - distance = ground elevation. Distance = (travel time) * (speed of light) / 2
What is a "return" in Lidar? What is a "return" measuring?
Measuring the return → bounce back of the pulse to the sensor (energy gets reflect, absorbed, and transmitted) → same thing happens with laser beams
What are the two types of laser beams that lidar uses and what wavelengths are they?
Need something to generate a laser beam Laser beam is a little piece of energy shot at a particular wavelength Piece of NIR light (1064 nanometers) *water absorbs almost every energy that gets thrown at it (will absorb NIR) So we use bathymetric lidar → green light (532 nanometers) Water will reflect a small amount of green light
What is the difference between passive and active remote sensing systems?
Passive: satellite/drone/plane picked up reflection of energy from the sun. sensor did not generate its own energy Active: sensor (satellite/plane/drone) generates its own source of energy → sends it down and collects the return
Why are two types of beams necessary with Lidar?
Piece of NIR light (1064 nanometers) *water absorbs almost every energy that gets thrown at it (will absorb NIR) So we use bathymetric lidar → green light (532 nanometers) Water will reflect a small amount of green light
What is point cloud data? What value is attached to it?
Point cloud data is the lidar data we acquire. Generates millions of points → gives rough image you can make measurements from All of the measurements we've made Lidar data ~ Point Cloud Data Choose what data we model in GIS Elevation values ??
What is the end result of extruding points in GIS? Extruding lines? Extruding polygons?
Points become poles, Lines became walls, and polygons become blocks.
What are Mass Points (in relation to a TIN)?
Points we use to actually build the TIN Most important points for elevation or elevation change on the landscape
How is a Thiessen Polygon constructed and how is it used to triangulate the TIN?
Polygons created around points with equal distances to the lines between points Equadistance between 2 points Then connect nodes to form triangles Perp to polygons Get most amount to be delaunay triangles
How does an offset function in 3D GIS?
Raises things above ground prior to extrusion. Some sort of vertical value, lifts things off the ground.
What does extrusion do in 3D GIS?
Represents giving each polygon a z value, raising it up to a particular height. Extrudes, by letting polygons grow or extend upward. 3 types of extrusion Extrudes straight up from imagery that is draped over a surface. Extrusion added to polygon feature base height values. Polygon extrusion applied from minimum z value Polygon extrusion applied from max z value.
How do breaklines affect the creation of a TIN? What does a TIN created without breaklines lack?
Select which points go into that tin Tins without breaklines will connect nodes not accounting for flat structures (roads river valley) Surface discontinuities will not show up if they are not added as hard breaklines
How many Lidar pulses are used in measurements and what is the vertical accuracy of Lidar?
Sends out 30,000 - 250,000 pulses per second Laser footprint where the beam is striking the ground (size of a dime) Vertical resolution of 15-30 cm Measure the height of what the laser beam is striking (make vertical measurements) 15-30 cm accuracy
What are the steps in calculating a least-cost path?
Shortest path = least cost path. Least amount of cost built into it Cost-weighted grid Total cost to traverse every cell Cost weighted distance Distance from source to every cell Least cost path Shortest distance
How can a realistic 3D model created in a program like SketchUp be used in ArcGIS Pro? What steps are involved in this process?
Sketch up: 3d design Start with georef imagery Design anything with sketchup tools Allows us to create very detailed 3d models More than polygons with textures point around the sides. Can create depths and particular features. - Take 2.5 model, convert to multipatch - Replace multipatch with Collada file
What is COLLADA? How is COLLADA used in 3D design and visualization in GIS?
Sketchup(3d design files): convert to COLLADA Collaborative Design Activity (COLLADA) Format can be read by many types of software (including pro) Many people can use and work on collada data Ends with extension [ .dae ] Moves from 2.5D to actually 3D Start with original extruded polygon with a single z value for each point (2.5d) Convert 2.5D, into multipatch And replace multipatch with Collada file -A universal format that can be used in most 3D design programs. (COLLAborative Design Activity) file type is (.dae)
What sort of factors would be constraints when building a Cost-Weighted grid?
Slope Weather Land use
How are slope and slope aspect represented in a TIN?
Slope: generate for each triangle inside the model Slope Aspect: gives same results as a DEM for each triangle
What is a LAS file and what does it contain?
Standard format for working with lidar data Hold all the point cloud data To work with multiple files together → bring them together in a LAS dataset
In calculating raster cost distance, what is the difference between a lateral link and a diagonal link? How are these distances computed?
Start in center of a cell to the center of the next cell Lateral link Diagonal link
How can a TIN be created using the Delaunay Triangulation Method?
Start with set of points. Around points create polygons (thiessen polygons) Use as a guide (line prep to polygon) to create polygon
How is Euclidian distance calculated (in relation to rasters)?
Straight line distance (as the bird flies)
What is the result of a Euclidian Distance raster calculation?
Straight line distance in one unit direction along the plane
What is a "bare-earth" Lidar DTM model? How is it constructed?
Take DSM and convert to a DTM model. Referred to a "bare-earth" model Just the heights of the bare earth Strips out all other returns EXCEPT the last return
How do terrain and scale affect the choice of contour interval on a map?
Terrain: mountainous terrain will need wider contour interval (less lines → less cluttered map) Flat terrain would use a narrow interval (relatively flat → no steep variations in elevation) Scale: small scale map need wide lines (a lot of data to show) Large scale map could use narrow lines ( less data to show)
How is a Cost-Weighted grid generated?
Total cost to traverse every cell Take DEM and calculate slope of the area Include a ranking (group into a cost ranking) Slice Take high degree of values and break into smaller classifications Slope and land use classifications can be classified to create new slope and cost
What is a TIN? What are the features of a TIN? How does a TIN represent a model of terrain?
Triangulated Irregular Network Second way of representing terrain Generate surface as a series of triangles representing a chunk of the terrain value. Entire surface connected but not overlapping triangles Irregular (not regularly spaced data) Each z value stored at points of triangles Network: way to make sure points are connected in a logical fashion Terrain: represent main features using points (z values) and triangle to represent patch of the surface. Subdivide terrain into triangles. Elevation point measurements at key places and joined together with triangles that form the actual surface
What are the advantages and disadvantages of using a TIN to model terrain?
Used a lot with GIS → much different way to approach DTM Advantages: Flexibility of data sources Can add points Good display Efficient Disadvantages: Needs large storage capacity Computationally difficult/complex (to work with)
What is vertical exaggeration and how does it affect surfaces and objects in 3D display?
Used for changing the z values of what were looking at in the scene For visualization purposes can give an area relief Multiply every z value in the area by a certain amount Used for visual purposes only Leaves horizontal scale the same NOT vertical scale DON'T take vertical measurements
What is Path Distance and what factors are necessary to calculate it?
Uses the same concepts but more complex problem Adds more variables on Plum modeling (what direction airborne pollutants will move in) Several factors are used in figuring out path distance (wind, fuel, uphill - more cost, downhill - less cost)
What is a contour interval?
Vertical distance between contour lines
What is VIP and how is it part of the TIN creation process?
Very Important Points GIS scans the entire area we are looking at (source) Algorithm (VIP) that picks out what it thinks are the most important points of the landscape (rapid changes, highest, and lowest) Calls them mass points : what we use to actually build the TIN
How can TINs be displayed in pseudo-3D in GIS?
Working with a scene 2D 3D and elevation surface Use the TIN as the elevation surface so any analysis draws from the TIN itself
How are 3D objects (such as 3D cars or trees) created and displayed in GIS (i.e. how do you start with a digitizing point and end up with a realistic looking 3D object)?
You can pull data from and use a 3 dimensional design program. Can work with predesigned data or build data yourself. Start with 2-d imagery Digitize points Convert map to scene (points become 3d) Set digitized points as 3d layer Select 3d symbology for point 3d symbology is displayed
What is a multipoint feature class and how is it used with Lidar data?
arcGIS Pro means of holding various xyz coordinates in LAS files as a layer you can work with in Pro. Holds millions and millions of points Designed to work like any other layer → but holds millions of points in a multipoint feature
What is a Terrain dataset and how does it relate to Lidar data?
arcGIS spatial data format → designed to be a tin that can hold millions and millions pf points from lidar Works by creating a tin based on the large number of points → only showing the area zoomed into at high resolution (not the entire area)
Lidar acquired
→ free through The National Map (3dep DEMs) option for elevation (source data) Youngstown area is available (Mahoning County)