# Questions tagged [map-algebra]

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

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659 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 ...
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 ...
93 views

### How can I stop my map algebra being limited to the size of my smallest raster?

I have five input rasters and I'm using map algebra to find areas where all of them have a value over 75, areas where all of them are over 25, and areas where one or more are under 25. I can do this ...
81 views

### Can I multiply fractions in map algebra?

I have a couple of rasters that show % of success in different things. I want to calculate the overall probability of success. The numerical values are integers so they represent the percentage. This ...
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 ...
2k views

### Using Raster Calculator expression in Python

I've posted about this problem before but I've got a few new questions. So here's the problem. I have two rasters containing bathymetry data: one containing the bathymetry of the sea floor, we'll ...
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 ...
146 views

### How to correctly input complex multiband functions in Raster Calculator?

I'm trying to compute a MTVI2 (Modified Triangular Vegetation Index - Improved) and EVI (Enhanced Vegetation Index) from Landsat 8 imagery. My formulas are as follow (I'm using ModelBuilder): MTVI2= ...
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 ...
93 views

### Automating Raster Calculator [duplicate]

I am seeing mixed answers on other posts so I thought I would ask here. Is there a way to automate the raster calculator? I am trying to create a series of inundation maps at fine increments. It ...
521 views

### ArcGIS Raster Calculator won't work in main model

I've created a sub-model in ArcGIS, which stretches my raster data to new values. The strange thing is, that the model works, if I run it itself - as soon as I implement it in the main model, I get ...
2k views

### QGIS from console: raster algebra

I'm newbie to programming in pyqgis. I need to perform a simple "GeoTiff * A" type of calculation(where A is a constant), but I am struggling to do so. I tried processing.runalg('saga:...
886 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 ...
382 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 ...
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 ...
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 ...
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 ...
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 ...
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,...
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....
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 ...
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 ...
670 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 ...
1k views

### How to compare two rasters and reclass the greater value(python script)?

I am working on an assignment that requires us to reclass a raster(via python) from two rasters. We need to compare the power received at one cell(on raster1) and compare it to the same cell on 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, ...
207 views

### How to iterate RGB raster layers in ModelBuilder?

I have an RGB raster that I'm calculating color-based indices from. When I do the calculations manually, I can select a certain band of the RGB raster to calculate. I need to do the same operations on ...
3k views

### NameError: name 'Con' is not defined

I have 365 rasters with the same extent, and I am trying to sum them together by month. I have the script below, which was working until I added the line out1 = Con(IsNull(raster), 0, raster) which is ...
63 views

### Map algebra from QGIS python console? [duplicate]

What command do I use to do map algebra on rasters from the QGIS python console?
2k views

### Map Algebra - Grass GIS (r.mapcalc) merge two raster with NoData value

I have a slope raster and a road raster. The black pixels in the road raster are NoData values and the pink pixels have a value of 1. They don't cover exactly the same area. I want to create a new ...
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, ...
544 views

### Map algebra expression with dynamic raster layers

Attached is the model that i am working on. The "To Value" and "From Value" are model parameters and hence subject to change each time according to requirements, This leads to varying number of files ...
664 views

### Raster produced by Con expression not saving

I cannot get a Con expression to work. Or, if it is working, I cannot get the raster produced by the Con expression to save. I have two rasters and I want the positive difference between the two, and ...
690 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 ...
2k views

### Piping output of Iterate Raster tool into Raster Calculator tool using ModelBuilder?

ArcGIS v10.1 ModelBuilder Using ModelBuilder and map algebra, I want to compute a ten year average grid from a stack of 10. The problem is that only 1 grid (%raster%), the last one through the ...
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 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 ...
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%". ...
203 views

### Map Algebra in VB.NET Add-In Tool

I'm trying to run a map algebra expression in a vb.net add-in, and can't seem to get it to work. It's a roving window that interpolates noData areas in a DEM. The expression works in the Python window,...
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 ...
772 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....
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 ...
663 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 ...
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, ...
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 ...
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. ...