**7. Issues (still) remaining: Some limitations persisting and potentialities observed**

Contribution of New Sensors to Cartography 195

trying to extract an amount of information proportional to the desired scale, they perceive that it is impossible. In some of these cases the user may reach the conclusion that the maximum scale that can be reached for the product in terms of geometry can be very different from the maximum scale reached in terms of information contents available in that product. However, in other cases it is also possible that the user does not even perceive such

The authors have no intention to criticize the performance of assessments regarding only accuracy. Actually, what we have been doing mostly, in a systematic way, is this type of assessment. The interest lies in calling attention for the need to complement the assessments with considerations regarding accuracy of the represented contents. As the existence of a critical mass regarding the need for assessments for accuracy of geometry is already perceived, it is desired to create a demand for investigations regarding the contents of what

As an example of such duality in the assessment of accuracy for the case of orbital images, we can mention the ALOS/PRISM in [16] planialtimetric data assessment report and in [19] on planimetric assessment of AVNIR2 images. Both texts present the maximum scales in terms of planialtimetric and planimetric accuracy, respectively, mentioning that the products may not allow the extraction of elements in the same scale. In order to know this last information it would be necessary to carry out an assessment of the images

It is also important, to minimize the intensity of a statement – which is sometimes mentioned – that for thematic cartography, geometry may be neglected, while for reference cartography geometry is all that matters. Due to this, many thematic maps present serious geometry problems, which makes them incompatible for the foreseen scale, likewise as in reference cartography one may find maps – often adjacent to each other – that present different information densities, or even, a lack of standardization of what is being

It is necessary to think about the problem, to suggest solutions and create a form of assessment that is really viable for the use by several producers of cartographic data – whether referential or thematic, whether originated from official mapping agencies or private companies, research groups, etc. who handle these types of data. What matters is to invest in the proposition of standards for assessment of such data. These standards should be appropriate for the new techniques for data acquisition and handling, considering the

When we consider the use of remote sensing data – whether originated from aerial or orbital levels – a set of cares is necessary, starting with the appropriate sensor choice, the time of the year for data acquisition, but treatment of the data and extraction of the desired information. People often say that the only optimal solution is the one obtained through photogrammetric survey. And for many applications it really is the best. But a survey carried out in the scale and dates desired is not always available. And for other applications

digital context and dealing with accuracy in terms of geometry and contents.

difference and will end up making inappropriate use of that data.

is represented.

interpretability.

represented.

Besides being somewhat limited, the evaluations using PEC made sense for analog mapping, whose construction processes were more vulnerable to graphic issues, such as the tracing of the elements properly. Considering altimetry, it becomes even less valid for the digital data, because reference is made to the contour lines interval, without mentioning specific scales. In several applications, nowadays, it is possible to have a DTM or DEM and, based on them, automatically extract the contour lines, in case required. But what matters is that the primary product tends to be the digital model and not the contour lines, which are dispensable for most of the applications, except in the case when it is desired to print the base with the altimetry represented in a way to allow quantitative estimates. According to this reasoning, it is necessary to assess the accuracy of the DTM or DEM, because they normally are inputs from derived products, although the official Brazilian norm does not make any reference to this type of product. Obviously one should maintain the assessment of the contour lines in the cases where they represent the altimetry.

Even considering the PEC as reference, it can only be applied for assessment of the geometry of reference cartography products. There is no official norm for assessment/evaluation of thematic cartography products in Brazil. Therefore, thematic mappings present accuracies – both in terms of geometry as contents – which are either not assessed or which remain to be decided by the specifications of their producers. The importance of the establishment of norms is emphasized once more, or, at least the establishment of national standards that facilitate data interchange with levels of accuracy that can be known and compared. Brazil is presently making an endeavor to divulge its National Spatial Data Infrastructure (INDE), expanding the utilization of geospatial data in an appropriate manner. Such an endeavor also focuses on the adoption and dissemination for the use/generation of metadata. In this context, the knowledge of the accuracy of the products, whether referential or thematic, is mandatory.

It is clear that both for the reference cartography as for the thematic cartography the assessment should not be restricted to the accuracy of the geometry, but should consider also the reliability of what is being represented – i.e., its actual contents. In this context, some items to be considered are: what is represented, the amount of elements presented, the taxonomic level reached, the level of detail, etc. Obviously, for reference cartography some elements may have greater relevance while in the thematic cartography others may deserve more attention. It is necessary to disseminate among the users and producers of cartographic data the importance to know the quality, both of the geometry as the contents, the detailing of the mapping, always assessed considering the scale adopted. Despite seeming obvious, it is quite common to find the distribution of products presented as compatible with a certain scale, but in the assessment made, one finds that the concern was merely with the accuracy for geolocation, i.e., with the geometry. Among the non-specialist users the problem is even greater, because they rely more easily on the information provided and end up acquiring products which do not correspond to their needs and, when trying to extract an amount of information proportional to the desired scale, they perceive that it is impossible. In some of these cases the user may reach the conclusion that the maximum scale that can be reached for the product in terms of geometry can be very different from the maximum scale reached in terms of information contents available in that product. However, in other cases it is also possible that the user does not even perceive such difference and will end up making inappropriate use of that data.

194 Cartography – A Tool for Spatial Analysis

**observed** 

**7. Issues (still) remaining: Some limitations persisting and potentialities** 

Besides being somewhat limited, the evaluations using PEC made sense for analog mapping, whose construction processes were more vulnerable to graphic issues, such as the tracing of the elements properly. Considering altimetry, it becomes even less valid for the digital data, because reference is made to the contour lines interval, without mentioning specific scales. In several applications, nowadays, it is possible to have a DTM or DEM and, based on them, automatically extract the contour lines, in case required. But what matters is that the primary product tends to be the digital model and not the contour lines, which are dispensable for most of the applications, except in the case when it is desired to print the base with the altimetry represented in a way to allow quantitative estimates. According to this reasoning, it is necessary to assess the accuracy of the DTM or DEM, because they normally are inputs from derived products, although the official Brazilian norm does not make any reference to this type of product. Obviously one should maintain the assessment

Even considering the PEC as reference, it can only be applied for assessment of the geometry of reference cartography products. There is no official norm for assessment/evaluation of thematic cartography products in Brazil. Therefore, thematic mappings present accuracies – both in terms of geometry as contents – which are either not assessed or which remain to be decided by the specifications of their producers. The importance of the establishment of norms is emphasized once more, or, at least the establishment of national standards that facilitate data interchange with levels of accuracy that can be known and compared. Brazil is presently making an endeavor to divulge its National Spatial Data Infrastructure (INDE), expanding the utilization of geospatial data in an appropriate manner. Such an endeavor also focuses on the adoption and dissemination for the use/generation of metadata. In this context, the knowledge of the accuracy of the

It is clear that both for the reference cartography as for the thematic cartography the assessment should not be restricted to the accuracy of the geometry, but should consider also the reliability of what is being represented – i.e., its actual contents. In this context, some items to be considered are: what is represented, the amount of elements presented, the taxonomic level reached, the level of detail, etc. Obviously, for reference cartography some elements may have greater relevance while in the thematic cartography others may deserve more attention. It is necessary to disseminate among the users and producers of cartographic data the importance to know the quality, both of the geometry as the contents, the detailing of the mapping, always assessed considering the scale adopted. Despite seeming obvious, it is quite common to find the distribution of products presented as compatible with a certain scale, but in the assessment made, one finds that the concern was merely with the accuracy for geolocation, i.e., with the geometry. Among the non-specialist users the problem is even greater, because they rely more easily on the information provided and end up acquiring products which do not correspond to their needs and, when

of the contour lines in the cases where they represent the altimetry.

products, whether referential or thematic, is mandatory.

The authors have no intention to criticize the performance of assessments regarding only accuracy. Actually, what we have been doing mostly, in a systematic way, is this type of assessment. The interest lies in calling attention for the need to complement the assessments with considerations regarding accuracy of the represented contents. As the existence of a critical mass regarding the need for assessments for accuracy of geometry is already perceived, it is desired to create a demand for investigations regarding the contents of what is represented.

As an example of such duality in the assessment of accuracy for the case of orbital images, we can mention the ALOS/PRISM in [16] planialtimetric data assessment report and in [19] on planimetric assessment of AVNIR2 images. Both texts present the maximum scales in terms of planialtimetric and planimetric accuracy, respectively, mentioning that the products may not allow the extraction of elements in the same scale. In order to know this last information it would be necessary to carry out an assessment of the images interpretability.

It is also important, to minimize the intensity of a statement – which is sometimes mentioned – that for thematic cartography, geometry may be neglected, while for reference cartography geometry is all that matters. Due to this, many thematic maps present serious geometry problems, which makes them incompatible for the foreseen scale, likewise as in reference cartography one may find maps – often adjacent to each other – that present different information densities, or even, a lack of standardization of what is being represented.

It is necessary to think about the problem, to suggest solutions and create a form of assessment that is really viable for the use by several producers of cartographic data – whether referential or thematic, whether originated from official mapping agencies or private companies, research groups, etc. who handle these types of data. What matters is to invest in the proposition of standards for assessment of such data. These standards should be appropriate for the new techniques for data acquisition and handling, considering the digital context and dealing with accuracy in terms of geometry and contents.

When we consider the use of remote sensing data – whether originated from aerial or orbital levels – a set of cares is necessary, starting with the appropriate sensor choice, the time of the year for data acquisition, but treatment of the data and extraction of the desired information.

People often say that the only optimal solution is the one obtained through photogrammetric survey. And for many applications it really is the best. But a survey carried out in the scale and dates desired is not always available. And for other applications the optimum solution may be a survey carried out by radar. Other times we find people who do not even think of using photographs, because beforehand they state that the solution is through the use of orbital data. But it may happen that in this type of survey you may not get the acquired image with the geometry and/or level of detailing most appropriate for your application. In other words, the choice of the sensor should be made by an evaluation comparing costs and benefits, focused on the application. Each option normally presents benefits and drawbacks which should be evaluated case-by-case.

Contribution of New Sensors to Cartography 197

photogrammetric flights for systematic cartography are again being contracted in greater quantity, making more data aimed at greater scales available (mainly 1:25,000 or above), in addition to a growing offer of LIDAR and RADAR data. Regarding this latter sensor - the project "Amazon Radiography" is presently ongoing, with the use of airborne interferometer RADAR, in the X and P bands, for production of a cartographic reference

One feature that may soon become more common for orbital sensors is the planning of Earth observation missions that count with a constellation of satellites as for instance, Rapideye. Obviously, besides technical issues, the constellations tend to favor the reduction of interval

Another important remark is the appearance of new spectral bands of high spatial resolution, such as the coastal, yellow and red edge, which offer new investigation

With increasingly better orbital and attitude control systems, image suppliers have been offering products with geolocation which are increasingly accurate, at least in areas with flat topography. In some cases those images may even dispense the need for geometric correction for users who work in scales which do not demand great accuracy. Orthorectified images can even be acquired for some products, without the need for the user to supply

The possibilities seem endless, with new offers of data and applications arising constantly. However, a critical eye should be kept on each input or product, in order to know their real

With the systematic offer of new and re-paged sensors, it is increasingly difficult to close a discussion on the subject. It is a fact that Remote Sensing is becoming indispensable for many cartographic applications, for all its already mentioned facilities. With all this, in the present phase, it is extremely important that the investments for assessment of so many products offered are made, in order to direct them to a conscious use, with awareness of the problems involved, thus avoiding loss of time and resources. The existent shift from analog to digital paradigm is also emphasized, which becomes an additional requirement in the

Still regarding the new sensors, one may state that the present scarcity of sensors of medium resolution has become a serious problem in mapping and monitoring of natural phenomena and events, mainly in countries with great territorial extensions such as Brazil. It is fundamental and urgent that investments be made in the sector. On the other hand, we emphasize our present concern with the maintenance and the investments in remote sensors that seek to meet the requirements of global studies (low resolution and great coverage), as in the case of climate changes, and local studies (high resolution), as for instance sensitivity

revisits, increasing the chance of success in the acquisition of data in the area desired.

base in scale 1:50,000 and 1:100,000, among other products in [21].

possibilities for the enhancement of thematic maps.

reassessment of methods and processes, not only of products.

and risk maps in support of natural disasters.

ground control points.

**8. Conclusion** 

potentialities and limitations.

Since the appearance and dissemination of high resolution (spatial) sensors, they became the source of the most desired images for several applications that work with medium to large scales. However, not always the spatial resolution is what matters. For several thematic applications, such as mapping of vegetation or land coverage and land use, the spectral resolution is a factor equally or more important than the spatial resolution. On the other hand, one problem which is often overlooked in the planning is the time that it may take to acquire an image (or pair of images) for a certain location. Even with sensors presenting a small revisiting period, for meteorological issues or for great data demand, months may pass until the data is effectively acquired, even if paying a priority rate. For several applications this may be a limiting factor.

There are other basic issues that are sometimes neglected: when choosing to pay an expressive amount for high spatial resolution images, it is assumed that the application is for scales that need greater detailing which, at their turn, demand also greater accuracy in terms of geometry. However it is not rare to find users who acquire such data and do not make the appropriate geometric modeling/correction – the orthorectification, with RPCs supplied by the satellite owner, GCPs (ground control points) with compatible accuracy and appropriate DEM. Even images with good internal geometry will present relatively high external errors if they are not well modeled, especially in areas with great attitude differences. And this is not acceptable in the immense majority of applications that effectively require data with great detailing.

Users of images that allow a more regional coverage – sensors normally included in the category of medium spatial resolution – should be feeling more difficulty to update data since Landsat 5 presented problems in November 2011 in [20], since there is practically no alternative that offers the same possibilities (especially considering cost and data availability). Environmental studies have a great demand for data of this category and need to search for alternatives, as the use of sensors of greater spatial resolution, normally losing spectral resolution – with highlight for the lack of availability of the SWIR band – in most of those sensors.

While the producers of thematic data are experiencing a certain period of low availability of these sensors of medium spatial resolution and highest spectral resolution, the opposite has been occurring for producers of reference cartographic data. These sensors of medium to high spatial resolution (between 2.5 and 5 meters), high (between 1 and 2.5 metros) and very high (below 1 m) can rely on a great offer of inputs. New sensors with higher spatial resolutions are becoming available almost every year. In Brazil, as mentioned before, photogrammetric flights for systematic cartography are again being contracted in greater quantity, making more data aimed at greater scales available (mainly 1:25,000 or above), in addition to a growing offer of LIDAR and RADAR data. Regarding this latter sensor - the project "Amazon Radiography" is presently ongoing, with the use of airborne interferometer RADAR, in the X and P bands, for production of a cartographic reference base in scale 1:50,000 and 1:100,000, among other products in [21].

One feature that may soon become more common for orbital sensors is the planning of Earth observation missions that count with a constellation of satellites as for instance, Rapideye. Obviously, besides technical issues, the constellations tend to favor the reduction of interval revisits, increasing the chance of success in the acquisition of data in the area desired.

Another important remark is the appearance of new spectral bands of high spatial resolution, such as the coastal, yellow and red edge, which offer new investigation possibilities for the enhancement of thematic maps.

With increasingly better orbital and attitude control systems, image suppliers have been offering products with geolocation which are increasingly accurate, at least in areas with flat topography. In some cases those images may even dispense the need for geometric correction for users who work in scales which do not demand great accuracy. Orthorectified images can even be acquired for some products, without the need for the user to supply ground control points.

The possibilities seem endless, with new offers of data and applications arising constantly. However, a critical eye should be kept on each input or product, in order to know their real potentialities and limitations.

## **8. Conclusion**

196 Cartography – A Tool for Spatial Analysis

applications this may be a limiting factor.

effectively require data with great detailing.

those sensors.

the optimum solution may be a survey carried out by radar. Other times we find people who do not even think of using photographs, because beforehand they state that the solution is through the use of orbital data. But it may happen that in this type of survey you may not get the acquired image with the geometry and/or level of detailing most appropriate for your application. In other words, the choice of the sensor should be made by an evaluation comparing costs and benefits, focused on the application. Each option

Since the appearance and dissemination of high resolution (spatial) sensors, they became the source of the most desired images for several applications that work with medium to large scales. However, not always the spatial resolution is what matters. For several thematic applications, such as mapping of vegetation or land coverage and land use, the spectral resolution is a factor equally or more important than the spatial resolution. On the other hand, one problem which is often overlooked in the planning is the time that it may take to acquire an image (or pair of images) for a certain location. Even with sensors presenting a small revisiting period, for meteorological issues or for great data demand, months may pass until the data is effectively acquired, even if paying a priority rate. For several

There are other basic issues that are sometimes neglected: when choosing to pay an expressive amount for high spatial resolution images, it is assumed that the application is for scales that need greater detailing which, at their turn, demand also greater accuracy in terms of geometry. However it is not rare to find users who acquire such data and do not make the appropriate geometric modeling/correction – the orthorectification, with RPCs supplied by the satellite owner, GCPs (ground control points) with compatible accuracy and appropriate DEM. Even images with good internal geometry will present relatively high external errors if they are not well modeled, especially in areas with great attitude differences. And this is not acceptable in the immense majority of applications that

Users of images that allow a more regional coverage – sensors normally included in the category of medium spatial resolution – should be feeling more difficulty to update data since Landsat 5 presented problems in November 2011 in [20], since there is practically no alternative that offers the same possibilities (especially considering cost and data availability). Environmental studies have a great demand for data of this category and need to search for alternatives, as the use of sensors of greater spatial resolution, normally losing spectral resolution – with highlight for the lack of availability of the SWIR band – in most of

While the producers of thematic data are experiencing a certain period of low availability of these sensors of medium spatial resolution and highest spectral resolution, the opposite has been occurring for producers of reference cartographic data. These sensors of medium to high spatial resolution (between 2.5 and 5 meters), high (between 1 and 2.5 metros) and very high (below 1 m) can rely on a great offer of inputs. New sensors with higher spatial resolutions are becoming available almost every year. In Brazil, as mentioned before,

normally presents benefits and drawbacks which should be evaluated case-by-case.

With the systematic offer of new and re-paged sensors, it is increasingly difficult to close a discussion on the subject. It is a fact that Remote Sensing is becoming indispensable for many cartographic applications, for all its already mentioned facilities. With all this, in the present phase, it is extremely important that the investments for assessment of so many products offered are made, in order to direct them to a conscious use, with awareness of the problems involved, thus avoiding loss of time and resources. The existent shift from analog to digital paradigm is also emphasized, which becomes an additional requirement in the reassessment of methods and processes, not only of products.

Still regarding the new sensors, one may state that the present scarcity of sensors of medium resolution has become a serious problem in mapping and monitoring of natural phenomena and events, mainly in countries with great territorial extensions such as Brazil. It is fundamental and urgent that investments be made in the sector. On the other hand, we emphasize our present concern with the maintenance and the investments in remote sensors that seek to meet the requirements of global studies (low resolution and great coverage), as in the case of climate changes, and local studies (high resolution), as for instance sensitivity and risk maps in support of natural disasters.

It is interesting that we are quickly reaching the point of discussing ethical and legal issues, such as the new limitations for the progress of orbital imaging at still greater detail levels, which reflect problems such as invasion of privacy and national security.

Contribution of New Sensors to Cartography 199

[9] TOUTIN, T. (2004) Comparison of Stereo-Extracted DTM from Different High-Resolution Sensors: SPOT-5, EROS-A, IKONOS-II, and QuickBird. IEEE Transactions on

[1] INPE. Notícias. (2010) Site: http://www.inpe.br/noticias/noticia.php?Cod\_Noticia=2148.

[2] GOOGLE. Google History. (2012) Site: http://www.google.com/about/company/history.

[14] BRASIL, Decreto 89.817 de 20 de junho de 1984. (1984) Estabelece as Instruções Reguladoras das Normas Técnicas da Cartografia nacional. Diário Oficial da República Federativa do Brasil, Brasília, n120, 22 de junho de 1984. Site: http://www.planalto.gov.br/ccivil\_03/decreto/1980-1989/D89817.htm. Último acesso: 10

[16] IBGE. Avaliação Planialtimétrica de Dados ALOS/PRISM Estudo de Caso: Itaguaí - RJ. (2009) Disponível em http://www.ibge.gov.br/alos/RelatoriodeAvaliacaoAlos.pdf.

[20] NASA. (2012) Landsat 5. Site: http://landsat.gsfc.nasa.gov/about/landsat5.html. Último

[3] FERNANDES, M. C. (2004) Desenvolvimento de Rotina de Obtenção de Observações em Superfície Real: uma aplicação em Análises Geoecológicas. Tese de Doutorado. IGEO /

[4] VICENS, R. S. (2003) Abordagem geoecológica aplicada `as bacias fluviais de tabuleiros costeiros no Norte de Espirito Santo: uma contribuição para avaliação e gestão de recursos hídricos. [Rio de Janeiro], 252p.(IGEO/ UFRJ), D.Sc., Geografia, Tese –

[5] GOMES, R. A. T. (2002) Modelagem de previsão de movimentos de massa a partir da combinação de modelos de escorregamentos e corridas de massa. [Rio de Janeiro], 102p.(IGEO/ UFRJ), D.Sc., Geografia, Tese – Universidade Federal do Rio de Janeiro,

[6] GUIMARÃES, R. F. G. (2000) Utilização de um modelo de previsão de áreas susceptíveis à ocorrência de escorregamentos rasos com controle topográfico: adequação e calibração em duas bacias de drenagem. [Rio de Janeiro], (IGEO/ UFRJ), D.Sc., Geologia, Tese –

[7] CORREIA, J. D. (2008) Mapeamento de feições deposicionais quaternárias por imagens orbitais de alta resolução espacial – Médio Vale do Paraíba do Sul. Tese Doutorado,

[11] SANTOS, P. R. A. (2005) Avaliação da Precisão Vertical dos Modelos SRTM em Diferentes Escalas: Um Estudo de Caso na Amazônia. Dissertação de Mestrado. IME.

Geoscience and Remote Sensing. 42(10):2121-2129.

**Online journal** 

Último acesso 29/03/**2012**.

Último acesso: setembro **2009**.

Universidade Federal do Rio de Janeiro, IGEO.

Universidade Federal do Rio de Janeiro, IGEO.

acesso: 10 de abril de 2012.

de abril de 2012.

**Theses** 

UFRJ.

IGEO.

IGEO/UFRJ.

Rio de Janeiro.

html#2005. Último acesso 29/03/**2012**.

In the case of Brazil, as in any other country, there is a choice of sensors which for several reasons become interesting, and which naturally prevail over the remaining, responding for the great majority of applications. In this investigation, we seek to focus those cases, trying to contribute for greater clarification regarding the potential and limitations of each option, limiting ourselves in this first approach to geometric issues. The 10 sensors presented here constitute the first phase of our investigation line, which will have continuity in the assessment of new sensors, such as Rapideye, Terrasar-X and Worldview 2. Another effort that is being developed, but which is still in an initial phase, is the diligent assessment of the potential of those products for extraction of the cartographic elements, a term which we call interpretability, whose scale of attendance tends to be less than the one defined by geometry.

The organization of the assessments carried out in three classes of scales was considered important for a better orientation of applications by the users. The limits adopted, using as important threshold the 1:25,000 scale, represent mapping challenges in Brazil, whose scarcity at this level of detail is immense. Considering the country's growth, the demand for reliable georeferenced information has increased a lot, which may translate a greater concern for its attendance by specialized institutions of the sector and, on the other hand, unfortunately, the explosion of individualized, and standalone solutions, in most cases, without the necessary control and knowledge. It is sought therefore, to contribute for the awareness of the community in general regarding those issues.
