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Questions tagged [map-algebra]

combining map data of similar dimension to produce new maps using algebraic operations

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What raster-based GIS systems really work?

Raster GISes like GRASS, ArcGIS/Spatial Analyst, and Idrisi can perform a rich set of data processing and analytical procedures loosely known as "map algebra." In today's computing environment it is ...
438 views

PostGIS raster summation (map algebra)

I have a table of polygons representing travel time isochrones on particular days. For each origin point, there are five isochrone geometries (stored in separate rows). For each origin point, I want ...
428 views

What are some Domain Specific Languages (DSLs) for GIS?

I'm curious what sort of domain specific languages (DSLs) are used in GIS. The only one I can think of is the DOCELL language that was provided in ArcInfo Workstation GRID, but is no longer supported....
1k views

Creating raster by randomly choosing cell value from multiple overlapping rasters?

I'm using ArcGIS Desktop 10 with its Spatial Analyst extension. How do I combine multiple rasters into one, always choosing randomly from the values of overlapping cells? I have an image that may ...
1k views

Performing raster map algebra in open source web GIS?

Map algebra for raster is easy with ArcGIS Raster Calculator (or QGIS). I had thought this would be easy with web GIS servers such as GeoServer and MapServer plus OpenLayers etc. as well. What I want ...
5k views

Using individual bands from multi-band image in ArcGIS raster calculator?

I'm trying to use individual bands from a multi-band TM image (IMG file) within the raster calculator in ArcGIS 10 (SP2/3). I can add individual bands to my MXD, but raster calculator will only use ...
2k views

Partially updating raster (DEM)?

How to update an .img DEM in ArcView 9.3? I do have DEM which need to be updated only if few parts. The area to be updated has been produced in separate DEM with Spline Interpolation with Barriers. ...
2k views

R giving error when attempting map algebra

I'm trying to manipulate some downloaded rasters using R, and keep getting the same error when I try to do any type of map algebra. The example below uses a raster file downloaded from http://www.csc....
4k views

For Loop - Map Algebra (ArcGIS) using Python

ORIGINAL QUESTION Im relatively new to python and these fourms but Im am having trouble utilizing for-loops for spatial analyses within ArcGIS. It does not appear to recognize the variable, ...
662 views

Map algebra in QGIS

How do you calculate standard deviation for each raster if you have set of rasters (100)? I was searching in raster calculator, but I didnt find it. Also google redirect me to using R or python. But I ...
738 views

Changing raster calculation values - shorten this script?

i'm doing something quite straightforward regarding raster algebra but am struggling either to find the correct function or make a function work correctly; Basically I have 2 rasters, representing ...
981 views

Compressing map algebra outputs from ArcPy?

When creating a raster map algebra output, is it possible to set its compression? I'm creating a model which generates many hundreds of rasters, and currently each is being stored without any ...
722 views

Error using con in Map Algebra in Python script

I am experiencing a painful problem in the middle of a Python script I am writing. When I get to a Map Algebra function, I have tried two different options and both return a different error. At first ...
1k views

How to do loops on raster cells with python console in QGIS?

I'm new here and beginner with python. I'm looking for a solution to my problem for some hours but now you are my last chance... I'm using the python (2.7.5) console in QGIS (2.4.0). Is there a ...
2k views

Map Algebra expression in a model fails on open workspace

I have model which runs 2 processes that create rasters and a third process that (attempts to) add the two of them using Map Algebra. The expression is very simple, just "%Raster_A%" + "%Raster_B%". ...
3k views

Access individual bands and use them in map algebra

I have a list of multiband rasters, consisting of: Red=Band 1, NIR=Band 2, SWIR1=Band 3 and SWIR2= Band 4. What I want is to access only the red and NIR bands and save it to new file. Then, I'll be ...
199 views

Passing additional arguments to ST_MapAlgebra callback?

I've written a custom callback function for ST_MapAlgebra and I want to pass additional arguments to it. The function is pretty useless - it just generates a raster filled with normal random values ...
121 views

Getting rid of small objects on raster in ArcMap?

What I want to do is to get rid of 'dark' objects which are on the green areas. My input looks like this: And I want my result to look like here: Raster value of green is 1, the rest has 0 value....
664 views

Change raster value for an area based on a class of another raster

I would like to change all raster values in raster A that fall into the locations of category/class 1 of raster B. Here, some more details. I did a calculation on a DEM resulting in different ...
346 views

PostGIS raster MapAlgebra callback optimization

I'm trying to speed up an ST_MapAlgebra callback function that essentially takes a raster with four bands, checks each band for values less than a given number, and where the check is true, return the ...
525 views

How to speed up raster/map algebra in PostGIS?

I am testing map algebra with PostGIS (2.1 with PostgreSQL 9.3) on two images, and found it to be rather slow. For example, dividing two images of 7200 * 3600 pixels took 110 ~ 120s on a desktop with ...
691 views

Nearest Neighbor Focal Statistics and Map Algebra

I would like to use a nearest-neighbor type analysis to iterate over a raster. The nearest neighbor analysis will give a cell value of 1 IF AND ONLY IF the cell being analyzed has a cell value larger ...
659 views

How to compute the ls factor equation for USLE model in qgis grass r.mapcalc

To compute the LS factor for the USLE model, the following equation easily works in ArcGIS. How can I perform the same in QGIS under GRASS r.mapcalc? LSfator = Power (("flowaccNW") * resolution/22.1,...
1k views

Calculate NDVI using ArcPy Spatial Analyst

My goal is to calculate NDVI using map algebra syntax. import arcpy from arcpy.sa import * red_band_raster = (r"C:\B3.tif") nir_band_raster = (r"C:\B4.tif") #Calculating NDVI float raster ...
3k views

Raster Multiplication - Can't Multiply Sequence by Non-Int of Type “Float”

I am trying to multiply a list of GRID raster datasets using a different value for each raster. The value is in the raster name. Some examples are [wse_1979_5,wse_1980_0,wse_1980_5], where 1979_5, ...
1k views

How to produce a mean raster file based on other raster files? [duplicate]

Possible Duplicate: Tools to flatten the jp2 to a single band (average the bands)? I have a number of raster files from a same area, that coordinates of corresponding pixels perfectly match one ...
115 views

Applying Map Algebra to List of Rasters and Saving New File in New Directory?

I am trying to multiply each raster by coefficient using Map Algebra in Python. I receive the following error for the code below: calcRaster.save(calcRasterName) AttributeError: 'unicode' object ...
3k views

Adding two rasters using map algebra in ArcPy?

I want to simply add two rasters within a python script using map algebra, which from what I understand is the equivalent to adding two rasters in the raster calculator. If I do this using raster ...
567 views

PostGis's ST_MapAlgebra rasters do not have the same alignment

I'm having a problem with ST_MapAlgebra. An error stating The set of rasters provided (custom extent included, if appropriate) do not have the same alignment is shown. I've been trying to know where ...
161 views

Problem with algebra formulas for work with gdal_calc.py

I'm trying to update some values of a raster based on another raster. 1st raster (A): landuse data (values from 10 to 240) 2nd raster (B): mask data (only nodata values and a given value, for ...
671 views

How to calculate cumulative sum conditionally across raster?

I don't know if this is possible without coding, but I need to: Create a raster file that, for each value in the input raster, sums all pixel values across the entire extent that are less than or ...
594 views

Efficiently check for equal adjacent values in raster calculator

I have a raster consisting of integer values in each cell. I want to check every adjacent cell in a 3x3 grid to see if any one of the adjacent cells has a value EQUAL to the center cell, and if so, ...
121 views

Checking if input raster exist or not in Raster Calculator?

I am with Raster Calculator in ModelBuilder on ArcGIS Desktop 10.2. In the Raster Calculator's Map Algebra expression window, I need to check if a Raster dataset has already existed or not. Can ...
205 views

Looping Map Algebra using Python

I am new to Python and am having difficulties trying to loop multiple rasters into a conditional statement. I want to extract all land-uses that have the value 21 from a folder with three different ...
565 views

ArcGIS raster calculator: ERROR 000539: Error running expression: rcexec() <type 'exceptions.ImportError'>: No module named collections

My raster is in the GRID format, source type is continuous and pixel type is floating point (32bit). If i use the raster calculator ("dem" *1000 or "dem >= 2m" (to highlight certain heights) it ...
53 views

How to weigh the size of a spatial event with respect to the number of its hotspots?

This is probably a map algebra problem. I have a 2D map with values ranging 0.0 to 1.0 spread all over it. The algorithm that produces them is an application of the fractional Brownian motion. The map ...
890 views

Plotting Vector Arrows from U and V Component with ArcGIS for Desktop?

I have two raster layers representing the U and V components of a vector wind. I could generate the magnitude raster by applying Square root in Map Algebra in ArcGIS. I also generated a raster layer ...
330 views

Map algebra from files in multiple directories

I'm a rookie in python programming. I want to do map algebra for multiple rasters but these rasters are in different folders. Here's the code ive created so far: #Importing modules import arcpy from ...
773 views

Spatial Analyst tool Look up but in ArcView3.2

Is there any option how to do a Spatial Analyst tool "Look up" operation from ArcGIS 10 in ArcView 3.2? I have a grid with attributes and need to "extract" values from the table field (values from 0....
73 views

Map Algebra loop only creating one raster

I'm trying to transform a bunch of rasters in arcpy according to specific functions to create suitability rasters. This portion of the code is supposed to find all the rasters with interpolated ...
411 views

Calculating Aerosol optical thickness from Landsat 7

EDIT I have added question down I am reading one paper and I found method to retrive AOT from landsat 7 image This should be simplifield equation, because they assumed observation zenit as 0. Than ...
384 views

Arcpy script for summing pixel values in loop can't handle large number of rasters

I want to sum the pixel values of large numbers of rasters of different extents (ArcMap v10.2). 16GB RAM. I have the following code (with help from this site) which solves the different extent ...
822 views

Nodata issues in map algebra

A dummy question. I need to change all values in my rasters into ones. I've been able to do this fine in the Rater Calculator just by multiplying the layer by zero and adding one (my_layer*0+1), but ...
66 views

Arcpy reclassify with function

I have two rasters, one with NDVI values, and one with greyscale values (=(red band + green band + blue band) / 3). The rasters have the same name. I need to reclassify them in arcpy with the ...
57 views

Showing two sets of points from two different fields in QGIS?

I made a union of two adjacent shp (points) files with the same theme (Geochemistry) so the resulting attribute table gave duplicated fields, for example: ID, As_ppm, Ag_ppm, Pb_ppm, ... , ID_2, ...
66 views

ArcPy map algebra equivalent for “any”?

I have binary (0-1) rasters. I'm trying to do an operation equivalent to: z = arcpy.sa.Con((Raster(a) | Raster(b) | Raster(c) | ... | Raster(y)) where the raster files a-y are dynamically generated ...
329 views

Identifying row and column location of a raster image using ArcGIS 10.1

The solution already available online gives a python syntax error ERROR 000989 Python syntax error: Parsing error SyntaxError: invalid syntax (line 1) when I write \$\$rowmap + 1 in map ...
1k views

Arcpy.Delete_management() not deleting folder?

I've written a script in Python that takes in two ascii files that represent surfaces, then convert them to Rasters, and finally Negate their values (i.e. multiply all cells by -1). In the script, I ...