The National Map is a suite of products and services that provide access to base geospatial information to describe the landscape of the United States and its territories. The National Map embodies 11 primary products and services and numerous applications and ancillary services.

The National Map supports data download, digital and print versions of topographic maps, geospatial data services, and online viewing. Customers can use geospatial data and maps to enhance their recreational experience, make life-saving decisions, support scientific missions, and for countless other activities. Nationally consistent geospatial data from The National Map enable better policy and land management decisions and the effective enforcement of regulatory responsibilities. The National Map is easily accessible for display on the Web through such products as topographic maps and services and as downloadable data. The geographic information available from The National Map includes boundaries, elevation, geographic names, hydrography, land cover, orthoimagery, structures, and transportation.

The majority of The National Map effort is devoted to acquiring and integrating medium-scale (nominally 1:24,000 scale) geospatial data for the eight base layers from a variety of sources and providing access to the resulting seamless coverages of geospatial data. The National Map also serves as the source of base mapping information for derived cartographic products, including 1:24,000 scale US Topo maps and georeferenced digital files of scanned historic topographic maps. Data sets and products from The National Map are intended for use by government, industry, and academia—focusing on geographic information system (GIS) users—as well as the public, especially in support of recreation activities. Other types of georeferenced or mapping information can be added within The National Map Viewer or brought in with The National Map data into a GIS to create specific types of maps or map views and (or) to perform modeling or analyses.

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The photon map is then stored on disk or in memory for later usage. Rendering (2nd pass) In this step of the algorithm, the photon map created in the first pass is used to estimate the radiance of every pixel of the output image. For each pixel, the scene is ray traced until the closest surface of intersection is found. If you tap on a folder, it will bring up a map with location dots to show the precise location where you took the photo. The same data is also visible on the Google Maps website:. When logged. Official MapQuest website, find driving directions, maps, live traffic updates and road conditions. Find nearby businesses, restaurants and hotels.

Sep 23, 2016 To see the map, open the Photos app, tap Albums, scroll to Places and open it. Tap the Map button at the top to see the pictures plotted on a map, or tap Grid to see them as thumbnails listed. Canada and United States of America Photo Map Maker. Cape Verde Photo Map Maker. Central African Republic Photo Map Maker.

National Map GIS data download and other related applications for working with our topographic data are available on our Data Delivery site.

The National Map (TNM) supporting themes include boundaries, elevation, geographic names, hydrography, land cover, orthoimagery, structures, and transportation. Other types of georeferenced or mapping information can be added within TNM Viewer or brought in with TNM data into a GIS to create specific types of maps or map views and (or) to perform modeling or analyses.


The 3D Elevation Program (3DEP) is managed by the USGS National Geospatial Program on behalf of the broader community with a goal of complete acquisition of nationwide lidar (IfSAR in AK) in 8 years to provide the first-ever national baseline of consistent high-resolution elevation data – both bare earth and 3D point clouds – collected in a time-frame of less than a decade. We also continue to be ready to meet growing needs for higher quality data, repeat coverage, and new products and services. These data serve government, public and private sector needs for a wide range of activities that include flood hazard mapping, precision agriculture, infrastructure planning and development, natural resource management, environmental assessment and a host of other applications.

NMCorps is an online crowdsourcing mapping project with volunteers successfully editing structures in all 50 States, Puerto Rico, and the U.S. Virgin Islands.

As part ofThe National Map, structures include schools, hospitals, post offices, police stations, cemeteries, and other important public buildings. By updating and verifying structures data, volunteers are making significant contributions to USGS National Structures Database, The National Map, and ultimately U.S. Topo Maps!

Anyone with an interest in contributing can volunteer. It is easy to sign up and get started! All you need is access to the internet, an email address, and a willingness to learn. “How to” documentation including a comprehensive User Guide and a Quick Start Guide will have you up and editing quickly. Begin editing in your own hometown or anywhere in the U.S., Puerto Rico, and the U.S. Virgin Islands.

Volunteers earn virtual badges for participating and are recognized for their contributions (with permission) via USGS and The National Map social media.

In computer graphics, photon mapping is a two-pass global illuminationrenderingalgorithm developed by Henrik Wann Jensen between 1995 and 2001[1] that approximately solves the rendering equation for integrating light radiance at a given point in space. Rays from the light source (like photons) and rays from the camera are traced independently until some termination criterion is met, then they are connected in a second step to produce a radiance value. The algorithm is used to realistically simulate the interaction of light with different types of objects (similar to other photorealistic rendering techniques). Specifically, it is capable of simulating the refraction of light through a transparent substance such as glass or water (including caustics), diffuse interreflection between illuminated objects, the subsurface scattering of light in translucent materials, and some of the effects caused by particulate matter such as smoke or water vapor. Photon mapping can also be extended to more accurate simulations of light, such as spectral rendering. Progressive photon mapping (PPM) starts with ray tracing and then adds more and more photon mapping passes to provide a progressively more accurate render.

Unlike path tracing, bidirectional path tracing, volumetric path tracing, and Metropolis light transport, photon mapping is a 'biased' rendering algorithm, which means that averaging infinitely many renders of the same scene using this method does not converge to a correct solution to the rendering equation. However, it is a consistent method, and the accuracy of a render can be increased by increasing the number of photons. As the number of photons approaches infinity, a render will get closer and closer to the solution of the rendering equation.



A model of a wine glass ray-traced with photon mapping to show caustics

Light refracted or reflected causes patterns called caustics, usually visible as concentrated patches of light on nearby surfaces. For example, as light rays pass through a wine glass sitting on a table, they are refracted and patterns of light are visible on the table. Photon mapping can trace the paths of individual photons to model where these concentrated patches of light will appear.


Diffuse interreflection[edit]

The photo mapping

Diffuse interreflection is apparent when light from one diffuse object is reflected onto another. Photon mapping is particularly adept at handling this effect because the algorithm reflects photons from one surface to another based on that surface's bidirectional reflectance distribution function (BRDF), and thus light from one object striking another is a natural result of the method. Diffuse interreflection was first modeled using radiosity solutions. Photon mapping differs though in that it separates the light transport from the nature of the geometry in the scene. Color bleed is an example of diffuse interreflection.

Subsurface scattering[edit]

Subsurface scattering is the effect evident when light enters a material and is scattered before being absorbed or reflected in a different direction. Subsurface scattering can accurately be modeled using photon mapping. This was the original way Jensen implemented it; however, the method becomes slow for highly scattering materials, and bidirectional surface scattering reflectance distribution functions (BSSRDFs) are more efficient in these situations.


Construction of the photon map (1st pass)[edit]

With photon mapping, light packets called photons are sent out into the scene from the light sources. Whenever a photon intersects with a surface, the intersection point and incoming direction are stored in a cache called the photon map. Typically, two photon maps are created for a scene: one especially for caustics and a global one for other light. After intersecting the surface, a probability for either reflecting, absorbing, or transmitting/refracting is given by the material. A Monte Carlo method called Russian roulette is used to choose one of these actions. If the photon is absorbed, no new direction is given, and tracing for that photon ends. If the photon reflects, the surface's bidirectional reflectance distribution function is used to determine the ratio of reflected radiance. Finally, if the photon is transmitting, a function for its direction is given depending upon the nature of the transmission.

Once the photon map is constructed (or during construction), it is typically arranged in a manner that is optimal for the k-nearest neighbor algorithm, as photon look-up time depends on the spatial distribution of the photons. Jensen advocates the usage of kd-trees. The photon map is then stored on disk or in memory for later usage.

Rendering (2nd pass)[edit]

In this step of the algorithm, the photon map created in the first pass is used to estimate the radiance of every pixel of the output image. For each pixel, the scene is ray traced until the closest surface of intersection is found.

At this point, the rendering equation is used to calculate the surface radiance leaving the point of intersection in the direction of the ray that struck it. To facilitate efficiency, the equation is decomposed into four separate factors: direct illumination, specular reflection, caustics, and soft indirect illumination.

For an accurate estimate of direct illumination, a ray is traced from the point of intersection to each light source. As long as a ray does not intersect another object, the light source is used to calculate the direct illumination. For an approximate estimate of indirect illumination, the photon map is used to calculate the radiance contribution.

Specular reflection can be, in most cases, calculated using ray tracing procedures (as it handles reflections well).

The contribution to the surface radiance from caustics is calculated using the caustics photon map directly. The number of photons in this map must be sufficiently large, as the map is the only source for caustics information in the scene.

For soft indirect illumination, radiance is calculated using the photon map directly. This contribution, however, does not need to be as accurate as the caustics contribution and thus uses the global photon map.

Calculating radiance using the photon map[edit]

In order to calculate surface radiance at an intersection point, one of the cached photon maps is used. The steps are:

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  1. Gather the N nearest photons using the nearest neighbor search function on the photon map.
  2. Let S be the sphere that contains these N photons.
  3. For each photon, divide the amount of flux (real photons) that the photon represents by the area of S and multiply by the BRDF applied to that photon.
  4. The sum of those results for each photon represents total surface radiance returned by the surface intersection in the direction of the ray that struck it.


  • To avoid emitting unneeded photons, the initial direction of the outgoing photons is often constrained. Instead of simply sending out photons in random directions, they are sent in the direction of a known object that is a desired photon manipulator to either focus or diffuse the light. There are many other refinements that can be made to the algorithm: for example, choosing the number of photons to send, and where and in what pattern to send them. It would seem that emitting more photons in a specific direction would cause a higher density of photons to be stored in the photon map around the position where the photons hit, and thus measuring this density would give an inaccurate value for irradiance. This is true; however, the algorithm used to compute radiance does not depend on irradiance estimates.
  • For soft indirect illumination, if the surface is Lambertian, then a technique known as irradiance caching may be used to interpolate values from previous calculations.
  • To avoid unnecessary collision testing in direct illumination, shadow photons can be used. During the photon mapping process, when a photon strikes a surface, in addition to the usual operations performed, a shadow photon is emitted in the same direction the original photon came from that goes all the way through the object. The next object it collides with causes a shadow photon to be stored in the photon map. Then during the direct illumination calculation, instead of sending out a ray from the surface to the light that tests collisions with objects, the photon map is queried for shadow photons. If none are present, then the object has a clear line of sight to the light source and additional calculations can be avoided.
  • To optimize image quality, particularly of caustics, Jensen recommends use of a cone filter. Essentially, the filter gives weight to photons' contributions to radiance depending on how far they are from ray-surface intersections. This can produce sharper images.
  • Image space photon mapping achieves real-time performance by computing the first and last scattering using a GPU rasterizer.


  • Although photon mapping was designed to work primarily with ray tracers, it can also be extended for use with scanline renderers.


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  1. ^Jarosz, Wojciech (September 2008). 'Chapter 7: The Photon Mapping Method'. Efficient Monte Carlo Methods for Light Transport in Scattering Media (PhD thesis). University of California, San Diego. p. 119 – via Dartmouth.

External links[edit]

Google Map Photos

  • Realistic Image Synthesis Using Photon MappingISBN1-56881-147-0
  • Photon mapping introduction from Worcester Polytechnic Institute

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